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OUTLINES 


PHYSIOLOGY: 


AN  APPENDIX 


PHRENOLOGY 


BY  P.  M.  ROGET,  M.D., 


SKCRETAHT    TO    THE    KOTAI    SOCIETY,    PHOFESSOR    OF    PHTSIOLGGT    IBT    THE    ROTAL 

INSTITUTIOK  OF   GREAT    BRITAIIf, 

ETC.    ETC. 


FIRST  AMERICAN  EDITION, 
REVISED,  WITH  NUMEROUS  NOTES. 


:<^0P 


0  'or 


PHILADELPHIA 


'a' 


LEA     AND     BLANC  M(^^yL,r       ^^1\V>^ 


(successors    to    CARET    AND    CO.)* 

1839. 


lYt^ 


Entehed,  according  to  Act  of  Congress,  in  the  year  1839,  by  Lea  and  Blan- 
cHARD,  in  the  Clerk's  office  of  the  District  Court  for  the  Eastern  District  of  Penn- 
sylvania. 


Printed  by  Haswell,  Barrington,  and  Haswell. 


AUTHOR'S   PREFACE. 


So  great  and  so  numerous  are  the  improvements  which  Phy- 
siology, in  all  its  departments,  has  received  since  the  period  of 
the  publication  of  the  former  edition  of  the  Encyclopesdia  Bri- 
tannioa,  that  it  was  deemed  necessary  by  the  Editor  to  give,  in 
the  present  edition,  an  entirely  new  Treatise  on  that  subject. 
When  I  engaged,  at  his  request,  to  write  this  Treatise,  I  was  far 
from  sufficiently  Estimating  either  the  magnitude  of  the  under- 
taking, or  the  space  to  which,  in  endeavouring  to  comprehend 
all  its  branches,  the  subject  would  extend.  The  limited  time 
which  was  assigned  me  for  its  completion,  and  my  distance  from 
the  place  of  pubHcation,  will,  I  trust,  be  admitted  in  extenuation 
of  whatever  errors  may  be  discovered  to  be  still  uncorrected. 

In  revising  the  article  Cranioscopy,  which  had  been  published 
in  the  Supplement  to  the  last  edition  of  the  Encyclopaedia,  and 
which  the  Ediltor  purposed  introducing  in  the  present  edition 
under  the  title  of  Phreivology,  making  such  additions  to  it  as  I 
might  think  were  requisite,  I  have  availed  myself  of  this  per- 
mission to  reply  to  some  of  the  criticisms  which  had  been  made 
upon  it  by  Mr.  G.  Combe  and  Dr.  A.  Combe:  it  was,  accord- 
ingly, thought  desirable  to  reprint  the  former  essay,  with  no 
other  alterations  than  a  few  verbal  corrections,  and  the  intro- 
duction of  a  few  sentences  descriptive  of  some  modifications  and 
additions  to  the  system  of  Gall  and  Spurzheim  contained  in 
Mr.  Combe's  System  of  Phrenology.     In  the  remarks  which  I 


4  PREFACE. 

# 

have  subjoined  to  that  essay,  the  reader  will  perceive  that  I  have 
refrained  from  entering  into  the  discussion  of  the  numerous  ob- 
jections that  might  be  urged  against  the  metaphysical  part  of  the 
modern  system  of  Phrenology,  having  neither  the  leisure  nor  the 
inclination  to  engage  in  controversies  of  this  nature. 

P.  M.  R. 

London,  Oct.  20,  1838. 


PREFACE 


THE    AMERICAN    EDITOR, 


The  contents  of  the  present  volume — as  will  be  seen  by  the 
Author's  Preface — form  the  articles  "Physiology"  and  "Phre- 
nology" in  the  seventh  edition  of  the  Encyclopaedia  Britannica. 
These  articles  have  been  recently  pubHshed  separately  in  Edin- 
burgh, in  two  handsome  volumes,  and  from  these  the  present 
edition  has  been  printed. 

Of  the  Author's  qualifications  as  a  physiological  writer,  it  is 
scarcely  requisite  to  speak.  The  fact,  of  his  having  been  selected 
to  compose  the  Bridgewater  Treatise  on  Animal  and  Vegetable 
Physiology,  is  sufficient  evidence  of  the  reputation  which  he  then 
enjoyed ;  and  the  mode  in  which  he  executed  the  task  amply 
evinces  that  his  reputation  rested  on  a  solid  basis. 

The  present  volume  contains  a  concise,  well-written  epitome 
of  the  present  state  of  Physiology — human  and  comparative — 
not,  as  a  matter  to  be  expected,  the  copious  details  and  devel- 
opments to  be  met  with  in  the  larger  treatises  on  the  subject ; 
but  enough  to  serve  as  an  accompaniment  and  guide  to  the  phy- 
siological student. 

The  attention  of  the  American  Editor  has  been  directed  to  the 
revision  and  correction  of  the  text;  to  the  supplying,  in  the  form 
of  notes,  of  omissions  ;  to  the  rectification  of  some  of  the  points 
that  appeared  to  him  erroneous  or  doubtful;  and  to  the  furnishing 

1* 


PREFACE. 


of  references  to  works  in  which  the  physiological  inquirer  might 
meet  with  more  ample  information. 

In  Phrenology,  the  Author  is  a  well-known  unbeliever,  and  his 
published  objections  to  the  doctrine  have  been  regarded  as  too 
cogent  to  be  permitted  to  pass  unheeded.  It  will  be  seen,  that 
farther  examination  in  the  interval  of  many  years,  which  has 
elapsed  since  the  publication  of  the  sixth  edition  of  the  Ency- 
clopaedia, has  not  induced  him  to  modify  his  sentiments  on  this 
head.  On  the  contrary,  he  appears  to  be  as  satisfied,  at  this 
time,  of  the  fallacy  of  the  positions  of  the  Phrenologist,  as  he  was 
at  any  former  period. 

Philadelphia,  July  1,  1839. 


CONTENTS 


CHAPTER  I. 
General  Views  of  Physiology         .        .         .        ,        Page  13 


1 

CHAPTER  n.  \ 

Application  of  Physiology        .        .        .         .        .        .        34 


CHAPTER  HI, 
Arrangement  of  Functions        ,         .         ,         .         •         .         47 

CHAPTER  IV, 
The  Vital  Powers     ,        ,        ,        ,        .         .        ,        .        5? 

CHAPTER  V. 

The  Mechanical  Functions — Organization  in  general — Comhina-- 
of  Textures — The  Cellular  Texture — Adipose  Texture — Membra' 


8  CONTENTS. 

nous  Structures  —  The  Osseous  Fabric — Cartilage  —  Fibro-Cartila- 
ginous  Structures — Ligamentous  Structures — Mechanical  Connex- 
ions— Articulation — Package  of  Organs — The  Integuments — The 
External  Integuments — Of  the  Internal  Integuments,  or  the  Mucous 
Membranes — Muscular  Action — Structure  of  Muscles — Muscular 
'  Contractility — Functions  of  the  Osseous  Fabric,  or  Skeleton — The 
-  Cranium— The  Face— The  Thorax— The  Spine— The  Pelvis— The 
Limbs  in  general — The  Lower  Extremities — The  Upper  Extre- 
mities      ..........         66 


CHAPTER  VI. 

Assimilation — Chemical  Constitution  of  Organized  Matter — Ne- 
cessity of  Aliment — Chemical  Conditions  of  Organized  Matter — 
Proximate  Animal  Principles — Gelatin  —  Albumen — Fibrin — Ar- 
rangement of  the  Functions  of  Assimilation — Properties  of  Food 
,  — Animal  Food  —  Vegetable  Food —  Condiments  —  Appetites  — 
Hunger — Thirst — Preparation  of  the  Food  for  Digestion — Mastica- 
tion— Insalivation — Deglutition — Digestion  or  Chylification         130 


CHAPTER  VIL 

Chylification — Properties  of  Chyle — Functions  of  Intestines — Pro- 
perties of  Bile — Functions  of  the  small  Intestines — Functions  of  the 
Spleen — Functions  of  the  large  Intestines — Lacteal  Absorption — 
Sanguification       .         . 16^ 


CHAPTER  Vm. 

Circulation — Apparatus  for  Circulation — Cardiac  Apparatus — San- 
guiferous System  in  general— Arterial  System — Venous  System— 


CONTENTS.  9 

Capillary  System — Phenomena  of  Circulation — Course  of  the  Blood 
in  its  Circulation — Proofs  of  Circulation — Powers  concerned  in  the 
Circulation — Action  of  the  Heart — Actions  of  the  Arteries — Action 
of  the  Capillaries — Action  of  the  Nerves — Pulmonary  Circula- 
tion        .         .         .         .    •      .         .         .         .         .         .         187 


CHAPTER  IX. 

Respiration — Mechanism  of  Respiration — Chemical  Effects  of  Res- 
piration— Animal  Temperature        .        •         »         •         •         2iQ 


CHAPTER  X. 

Secretion — Apparatus  for  Secretion — Glandular  Apparatus — Ar- 
rangement and  Properties  of  the  Secretions — The  Aqueous  Secre- 
tions-^ The  Albuminous  Secretions  —  Mucous  Secretions  —  The 
Fibrinous  Secretions — Oleaginous  Secretions — The  Resinous  Se- 
cretions— The  Saline  Secretions — Theory  of  Secretion      .        217 


CHAPTER  XI.    ,  -  ^ 

Absorption — Structure  of  the  Absorbent  System — Function  of  Ab- 
sorbents—  Venous  Absorption — Effects  of  Absorption — Function 
of  the  Lymphatic  Glands 233 


CHAPTER  XII. 

Excretion — Excretory  Function  of  the  Lungs — Excretory  Func- 
tion of  the  Skin — Excretory  Function  of  the  Kidyieys — Excretory 
Function  of  the  Liver     .        .....        .        240 


10  CONTENTS. 


CHAPTER  XIII. 

Nutrition — Ossification — Dentition — Nutrition  of  the  Softer  Tex- 
tures— General  Phenomena  of  Nutrition  .         .         .         244 


CHAPTER  XIV. 

The  Sensorial  Functions — General  Views — Organization  of  the 
Nervous  System — Organization  of  the  Brain  and  Spinal  Cord — 
The  Nerves — Ganglia 251 


CHAPTER  XV. 

The  External  Senses — Touch — Sensation  of  Pressure— Sensations 
of  Temperature — Anomalous  Sensations — Sensation  of  Pain — The 
Muscular  Sense.  Taste — Organs  of  Taste — Function  of  Taste. 
Smell — Organs  of  Smell — Function  of  Smell.  Bearing — Acoustic 
Principles — Organ  of  Hearing — Function  of  Hearing.  Vision- 
Internal  parts  of  the  Eye — External  parts  of  the  Eye — Optical  Prin- 
ciples— Formation  of  Images  in  the  Eye — Adjustments  for  the  Cor- 
rection of  Aberration         .......         259 


^  CHAPTER  XVI. 

Physiological  Laws  of  Sensation  —  Phenomena  of  Sensation  — 
Specific  endowment  of  the  Nerves  of  Sensation — Modifications  of 
Impressions — Conditions  necessary  for  Sensation — Theories  of 
Sensation 287 


CHAPTER  XVII. 

Locality  of  the  Sensorium — Requisite  conditions  of  the  Sensorium 


CONTENTS.  1 1 

—Laws  of  Recurrence  and  the  Association  of  Impressions— 
Volition  and  Voluntary  Motion— Automatic  Motions— Instinctive 
Motions—Involuntary  Motions— Psycological  relations  of  the  Sen- 
sorium — Sleep         •••.....         294 


The  Voice 


CHAPTER  XVIII. 
31S 

CHAPTER  XIX. 

Generation— General   Views— Unimpre gnat ed   Ovum— The  Male 

,  System— The  Female  System— Theories  of  Generation— Utero- 

Gestation— Parturition— Lactation— Fcetal  Evolution    .        326 

CHAPTER  XX. 

Progressive  Changes  in  the  Animal  Economy        .        .        35©, 


CHAPTER  XXI. 

Temperaments 


359 


CHAPTER  XXII. 
Varieties  of  the  Human  Species 354 


CHAPTER  XXHI. 

Comparative  Vii\siOhOGX— Comparative  Physiology  of  Mammalia 
—Peculiarities  of  the  Human  Conformation— Peculiarities  in  the 
Conformation  of  other  Mammalia  — Quadrumana—Chiroptera— 
Insectivora  —  Plantigrada—Digitigrada— Amphibia— Marsupialia  — 
Rodentia— Tardigrada— Monotremata— Pachydermata— Solipeda— 


12  CONTENTS. 

Ruminantia— Cetacea.  Comparative  Physiology  of  Birds— Gene- 
ral Description— Peculiarities  in  particular  Families  and  Genera  of 
Birds.  Comparative  Physiology  of  Peptiles—Ue^iWes  in  General 
—  Chelonia— Sauria— Ophidia— Batrachia.  Comparative  Physi- 
ology of  Fishes.  Comparative  Physiology  of  Mollusca—QeY>\i^- 
lopoda  — Gasteropoda— Acephala.  Comparative  Physiology  of 
Jlrticulata  —  Annelida  —Crustacea- Arachnida— Insects.  Compa- 
rative Physiology  of  Zoojj/tyfes— Echinodermata— Entozoa— Aca- 
lepha— Polypi— Infusoria 368 


CHAPTER  XXIV. 

History  of  Physiology    .        .        •        '       .'    ,  /        '        ^^^ 

kv^mmx— Phrenology ^55 


PHYSIOLOGY. 


j:!!"^        \ 


CHAPTER  I 

GENERAL    VIE  w"^  r* 


1.  Physiology,  or  the  science  of  animal  life,  has  been  variously 
defined  by  different  writers.  If  the  term  were  interpreted  strictly 
according  to  its  etymology,  it  would  carry  a  meaning  much  more 
extensive  than  is  warranted  by  common  usage  ;  for  being  derived 
from  ?ua-(f,  nature,  and  Koyai,  discourse,  its  proper  signification 
should  be,  the  science  of  nature.  It  might  accordingly  be  under- 
stood to  comprehend  inquiries  in  every  department  of  nature, 
both  animate  and  inanimate ;  and  might  indeed  be  regarded  as 
synonymous  with  physics,  or  natural  philosophy,  which  are 
othei'  expressions  of  corresponding  import,  but  ^yhich  at  present 
are  themselves  restricted  in  their  meaning  to  a  special  depart- 
ment of  nature.  There  can  be  no  doubt,  indeed,  that  such  must 
originally  have  been  the  real  signification  of  these  terms ;  but  it 
is  npedless  now  to  inquire  by  w4iat  gradual  transitions  they  have 
at  length  come  to  bear  such  different  and  even,  in  some  respects, 
opposite  significations.  If  we  were  desirous  of  substituting  a 
a  term  which  would  accurately  express  the  idea  now  associated 
with  the  word  physiology,  we  should  adopt  that  of  biology,  from 
/S'of,  life,  first  introduced  by  Treviranus,  who  has  written  a  Ger- 
man work  on  this  subject,  which  bears  that  title. 

2.  Natural  philosophy,  or  physics,  is  now  understood  as  desig- 
nating that  class  of  sciences,  wliich  have  for  their  object  the 
examination  of  the  properties  of  lifeless  matter ;  whilst  physio- 
logy, in  its  modern  acceptation,  is  in  like  manner  limited  to  the 
consideration  of  the  properties  which  are  peculiar  to  organized 
and  living  bodies.  The  former  is  conversant  only  with  nature  in 
her  dead  or  inanimate  condition;  the  latter  with  nature  endowed 
with  life,  and  in  all  its  various  forms  and  modifications.  ' 


14  PHYSIOLOGY. 

Thus  mechanics,  hydrostatics,  and  pneumatics,  wholly  relate 
to  the  general  phenomena  exhibited  by  matter  in  its  solid,  liquid, 
and  gaseous  forms ;  optics,  which  relates  to  the  phenomena  of 
light,  together  with  electricity,  magnetism,  and  the  science  of 
heat,  which  regard  other  classes  of  phenomena  produced  by 
peculiar  agents,  are  all  considered  as  branches  of  natural  philo- 
sophy. Chemistry,  which  is  concerned  with  the  changes  of 
composition  in  bodies,  resulting  from  the  mutual  action  of  their 
particles  at  insensible  distances,  ranks  also  with  the  sciences 
relating  to  the  properties  of  inorganic  matter,  and  of  which  the 
assemblage  constitutes  what  are  more  correctly  termed  in  the 
present  day,  the  physical  sciences. 

3.  On  the  other  hand,  the  study  of  animated  nature  does  not 
admit  of  the  same  extent  of 'subdivision.  Nature  has  indeed 
traced  a  broad  and  obvious  line  of  demarcation  between  the 
vegetable  and  the  animal  kingdoms ;  the  first  being  the  province 
of  botany,  the  second  of  zoology  ;  both  of  which  departments 
offer  us  a  wide  field  of  inquiry,  and  inexhaustible  subjects  of 
speculation.  But  it  is  in  the  animal  world,  more  especially,  that 
the  busy  and  ever-changing  scene  is  calculated  to  awaken  the 
most  lively  curiosity,  and  inspire  the  deepest  interest.  The 
multiplied  relations  which  connect  us  with  the  lower  animals,  the 
obvious  analogies  which  subsist  between  them  and  our  own 
species,  and  the  striking  evidences  of  power,  intelligence,  and 
benevolent  design  displayed  in  all  the  phenomena  they  present  to 
our  observation,  confer  on  the  study  of  animal  life  a  degree  of 
importance  which  belongs  to  scarcely  any  other  study. 

4.  But  the  foundations  of  all  science  must  be  laid  by  drawing 
accurate  distinctions  among  the  objects  which  come  within  its 
cognizance ;  by  making  a  strict  analysis  of  the  ideas  it  compre- 
hends, and  by  establishing  precise  definitions  of  the  terms  it 
employs.  As  in  all  the  other  departments  of  human  knowledge, 
we  can  arrive  at  general  facts,  or  comprehensive  laws,  only  by- 
submitting  to  the  previous  task  of  ascertaining  and  collecting 
individual  facts;  so  in  natural  history  we  find  it  necessary  to 
subdivide  our  labours  into  that  which  takes  cognizance  of  indi- 
vidual objects  only,  and  that  which  inquires  into  their  more 
general  relations  with  one  another.  The  first  is  properly  the 
history,  {he  second  the  philosophy  of  nature;  and  this  distinction 
we  may  observe  to  run  through  all  the  branches  into  which  the 
subject  is  divisable.  It  applies  even  to  astronomy,  in  which  the 
mere  physical  history  of  the  phenomena  forms  a  preliminary 
body  of  knowledge,  yet  subordinate  to  that  higher  range  of 
inquiry  which  establishes  connexions  between  these  phenomena, 
and  uni'es  them  into  comprehensive  laws  or  theories.  Minera- 
logy, again,  must  be  studied  as  the  foundation  of  geology ;  the 
former  being  the  history  of  the  actual  appearances ;  the  latter, 


^  GENERAL    VIEWS.,  15 

the  theory  of  the  series  of  changes  which  have  led  to  these 
observed  phenomena.  Thus,  also,  the  external  forms,  and  more 
obvious  habitudes  of  plants,  and  their  classifications  in  conform- 
ity w^ith  those  forms  and  properties,  constitute  the  subjects  of 
botany,  properly  so  called;  whilst  the  study  of  their  internal 
structure  and  economy,  with  relation  to  the  more  general  phe- 
nomena of  vegetation,  is  comprised  under  the  head  ot ph,ylology, 
or  the  physiology  of  vegetables. 

5.  In  like  manner,  the  proper  objects  of  zooIos;y  are  to  trace 
the  external  forms  of  animals,  to  distribute  and  arrange  them  in 
systematic  order,  and  to  record  the  particular  facts  relaling  to 
their  history  ;  that  is,  to  the  more  obvious  phenomena  which  they 
present  to  our  observation.  Physiology  embraces  a  wider  field 
of  research,  inquires  into  the  connexions  between  the  phenomena, 
and  investigates  the  causes  from  which  they  spring,  and  the  laws 
by  which  they  are  governed.  The  zoologist  is  content  with 
collecting  observations  on  the  visible  actions  of  animals,  on  their 
peculiar  habits,  modes  of  life,  and  the  manifestation  of  those 
faculties  with  which  they  are  respectively  endowed  by  the  Author 
of  nature;  a  pursuit  which  aflx)rds  inexhaustible  sources  of  amuse- 
ment, and  furnishes  abundant  matter  of  admiration  and  of  wonder. 
But  the  physiologist  aims  at  far  higher  objects ;  and  considering 
the  external  phenomena  presented  by  animals  as  lying  merely  at 
the  surface,  seeks  for  information  relative  to  the  causes  of  all  the 
facts  which  are  furnished  to  him  by  zoology,  by  examining  the 
interior  structure  of  their  bodies,  by  inquiring  into  the  movements 
of  that  interior  mechanism,  and  the  sources  of  those  various 
actions  which  give  rise  to  all  the  complicated  phenomena  of  life. 
An  extensive  and  even  boundless  region  of  knowledge  opens  to 
his  view  in  these  highly  curious  and  interesting  subjects  of 
research,  constituting  one  vast  science,  which,  although  consider- 
able progress  has  been  made  in  it  by  the  labours  of  our  prede- 
cessors, is  yet  destined  to  occupy,  for  an  incalculable  period  of 
time,  the  unremitting  elfbrts  of  succeeding  generations. 

6.  The  phenomena  of  living  beings  have  a  totally  different 
character  from  the  changes  which  take  place  in  inanimate 
matter;  and  are  with  more  difficulty  subjected  to  the  severe  ana- 
lysis required  by  inductive  philosophy.  The  properties  of  inor- 
ganic bodies  are  of  a  simpler  and  more  definite  nature,  and 
however  variously  they  may  be  combined  in  their  effects,  admit, 
in  general,  of  a  reduction  to  general  laws.  This  is  most  effec- 
tually  accomplished  by  means  of  experiments,  varied  in  such  a 
manner  as  to  reduce  each  class  of  phenomena  to  its  simplest 
conditions,  and  afterwards  combined  in  such  a  way  as  to  allow 
of  a  comparison  of  their  results  "with  the  appearances  presented 
by  nature,  and  of  thus  verifying  their  identity. 

But  it  is  hardly  possible  to  pursue  the  same  process  of  investi- 


16  PHYSIOLOGY., 

gation  to  any  extent  in  the  diversified  phenomena  of  organization. 
So  comphcated  is  the  mechanism,  and  so  fine  the  minute  struc- 
ture of  animal  and  vegetable  bodies,  that  they  elude  the  cogni- 
zance of  our  senses,  even  when  assisted  by  the  utmost  refinement 
of  optical  and  mechanical  art.  All  that  chemistry  has  yet 
achieved  in  disclosing  to  us  the  properties  of  different  species  of 
matter,  and  of  their  various  combinations,  falls  infinitely  short  of 
that  knowledge  which  could  enable  us  to  follow  and  to  under- 
stand the  curious  and  elaborate  series  of  chemical  changes  which 
take  place  in  the  interior  of  the  living  body.  Far  less  are  we 
competent  to  trace  the  operation  of  those  more  subtle  and  myste- 
rious principles,  which  are  the  springs  of  motion,  and  which 
regulate  the  actions  of  the  machine,  and  connect  the  whole  of  its 
movements  into  one  harmonious  system.  Judging  from  their 
more  obvious  effects,  indeed,  these  principles  appear  to  be  quite 
of  a  different  nature  from  those  which  produce  the  phenomena 
of  the  inorganic  world.  The  series  of  changes  which  are  exhi- 
bited by  an  animal  or  a  vegetable,  from  the  first  moment  o-f  its 
separate  existence,  through  all  the  stages  of  its  growth,  maturity, 
and  decline,  to  the  period  of  its  death,  are  far  too  complicated 
and  multifarious  to  admit  of  being  reduced  to  one  single  princi- 
ple, in  the  same  way  as  the  movements  of  the  heavenly  bodies, 
for  instance,  are  reducible  to  the  simple  law  of  gravitation. 

7.    Physiologists,    indeed,  not  deterred  by  these   difficulties, 
which  are  inherent  in  the  subject  of  their  researches,  have  in  all 
ages  attempted  generalizations  of  this  kind.     They  have  consi- 
dered all  the  actions  and  phenomena  which  are  pecuhar  to  living 
beings,  and  which  differ  from  those  exhibited  by  the  same  bodies 
after  death,  as  resulting  from  the  operation  of  a  single  principle 
of  life.     Different  designations  have  been  given  to  this  power  by 
different  theorists ;  thus,  some  have  called  it  fhe  vital  principle, 
others  the  spirit  of  animation,  the  archcBUS,  the  organic  force ; 
and  many  other  appellations  have  been  given  to  it,  according  to 
the  particular  taste  or  fancy  of  the  writer.    Nothing,  indeed,  can 
be  more  specious  than  this  reference  to  unknown  facts,  which 
have  a  manifest  connexion  with  one  another,  to  a  common  prin- 
ciple of  action,  or  in  other  words,  to  a  vital  power.     The  only 
idea  we  can  form  of  life  appears  to  imply  the  unity  of  such  a 
principle.    This  idea,  as  is  well  remarked  by  Cuvier,  is  suggested 
hy  the  observation  of  a  certain  class  of  phenomena,  succeeding 
each  other  in  an  invariable  "order,  and  having  certain  mutual 
relations  with  one  another :  yet  it  is  but  a  vague,  and  indistinct 
idea.     We  are  ignorant  of  the  nature  of  that  link  which  unites 
the  whole  of  these  phenomena :  but  the  existence  of  sdme  such 
link  forces  itself  upon  our  belief,  and  we  are  compelled  to  give  it 
a  particular  designation,  and  speak  of  it  as  if  it  were  something 
more  than  a  mere  fiction  of  the  intellect. 


GENERAL    VIEWS.  17 

8.  Those  who  are  unaccustomed  to  philosophical  reasonings, 
may  be,  indeed,  and  often  are,  decciv^ed  by  the  employment  of 
these  abstract  terms,  and  regard  them  as  the  expressions  of  a 
simple  law  of  nature,  of  the  same  comprehensive,  yet  definite 
character,  as  those  of  gravitation,  cohesion,  heat,  and  electricity. 
A  more  careful  and  profound  analysis,  however,  will  convince 
us  that  the  power  inherent  in  organization,  upon  which  its  infi- 
nitely diversified  actions  depend,  is  not  a  simple  agency,  but  a 
combination  of  several  powers,  not  only  different  from  the  phy- 
sical agents  which  actuate  the  inorganic  world,  butdifl^ering  also 
very  widely 'amongst  each  other.  In  order  to  arrive  at  this  con- 
clusion, however,  it  will  be  necessary  to  take  a  review  of  the 
phenomena  themselves,  and  we  shall  therefore  defer  the  consider- 
ation of  this  subject  to  a  future  chapter. 

9.  Although  the  peculiar  nature  of  the  phenomena  which  phy- 
siology embraces  has  hitherto  baffled  all  our  endeavours  to  obtain 
results  of  the  same  general  and  comprehensive  nature  as  those 
which  have  rewarded  our  efforts  in  the  purely  physical  sciences, 
yet  other  resources  are  open  to  us,  capable  of  conducting  us  to  a 
still  more  ample  and  inviting  field  of  inquiry.  Living  nature  is 
impressed  with  a  character,  which  at  once  raises  it  to  a  higher 
order  among  the  objects  of  human  intellect,  and  invests  the 
science  which  regards  it  with  a  more  lofty  and  ennobling  senti- 
ment. Life  is  peculiarly  characterised  by  the  manifestation  of 
INTENTION.  Adaptation  of  means  to  an  end  is  visible  throughout 
the  whole  of  this  animated  scene.  Express  design  is  palpably 
discernible  in  every  formation,  in  every  arrangement,  in  every 
series  of  changes  which  this  vast  theatre  of  nature  displays. 
Utility  is  the  governing  principle  of  all ;  intelligence  and  power 
far  exceeding  the  utmost  stretch  of  our  imagination,  are  revealed 
to  us  in  language  not  to  be  mistaken,  and  carrying  with  it  irre- 
sistible conviction.  Thus,  while  the  sciences  of  inorganic  matter 
are  founded  on  the  relations  of  cause  and  effect,  physiology  takes 
cognizance  more  especially  of  the  relations  of  means  to  ends, 
which  the  phenomena  presents  to  our  view.  Hence  we  obtain  a 
new  principle  of  arrangement  among  these  phenomena ;  hence 
also  arises  a  new  source  of  interest,  of  a  kind  very  superior  to 
that  which  mere  physical  relations  can  ever  inspire. 

10.  The  purposes  to  which,  pursuing  the  new  principle  of  ar- 
rangement, we  can  perceive  the  different  structures  which  com- 
pose an  animal  body,  are  subservient,  are  termed,  in  the  language 
of  physiology,  the  functions  of  those  parts.  Life  results  from 
the  exercise  of  these  functions,  and  consists  in  the  continued 
accomplishment  of  their  respective  objects.  The  principal  object 
of  physiology,  then,  is  the  study  of  the  functions  of  life  ;  that  is, 
the  investigation  of  the  changes  occurring  in  the  living  system 
with  reference  to  their  respective  objects,  and  in  their  subser- 

2* 


18 


PHYSIOLOGY. 


vience  to  the  maintenance  of  life,  and  the  various  purposes  for 
which  Hfe  was  bestowed.  We  shall  now  proceed  to  take  a 
general  review  of  these  functions,  in  order  to  establish  a  founda- 
tion for  the  divisions  of  (he  science  we  are  now  treating. 

11.  The  most  cursory  view  that  we  can  take  of  the  phenomena 
of  life  will  be  sufficient  to  show  that  the  functions  to  which  they 
are  referable  are  of  different  degrees  of  importance  with  relation 
to  the  objects  of  life.  Some  are  so  closely  connected  with  these 
objects,  that  their  continued  exercise  is  indispensable  to  the  very 
existence  of  life,  which  would  cease  if  they  were  for  a  moment 
interrupted.  Others,  which  are  less  immediately  concerned  in  the 
actual  maintenance  of  the  vital  actions,  are  yet  essential  to  its 
preservation,  and  cannot,  with  safety,  be  suspended  but  for  a 
very  short  interval.  Some  are  only  occasionally  called  into  play, 
and  others  are  so  remotely  useful,  as  to  admit  of  lying  dormant 
for  a  considerable  period,  or  even  of  being  dispensed  with 
altogether.  Some  functions  require  for  their  performance  the 
concurrence  of  others,  and  these,  again  imply  the  exercise  of 
many  more.  Some  are  of  a  more  isolated  nature,  and  have  less 
connexion  with  the  general  system  of  functions.  By  studying 
these  relations,  we  are  enabled  to  trace  a  certain  plan  in  the 
designs  of  nature,  and  a  certain  subordination  of  functions  suffi-, 
cient  to  guide  us  in  our  studies,  and  to  enable  us  to  trace  out  a 
tolerably  connected  order  of  subjects. 

1 2.  It  will  be  useful,  before  proceeding  to  the  details  of  the  subject, 
to  pi'esent  our  readers  with  a  general  sketch  of  the  system  of  the 
animal  economy,  which  may  serve,  indeed,  the  same  purpose,  as 
a  map  does  to  a  traveller,  imparting  a  general  notion  of  the 
bearings  and  relations  of  the  several  objects  of  interest  ih  the 
country  he  is  about  to  traverse.  We  shall  for  this  purpose, 
embrace  in  one  view  that  assemblage  of  functions  which  con- 
stitutes animal  life  in  its  most  complete  and  perfect  form,  and  in 
the  attainment  of  its  full  development. 

13.  All  the  functions  of  the  animal  economy,  all  the  mechanical 
dispositions  of  the 'system,  and  all  the  movements  of  its  parts,  are 
subordinate  to  two  great  objects ;  first,  the  preservation  and  wel- 
fare of  the  individual  being  which  they  compose;  and,  secondly, 
the  continuance  of  the  race  to  which  it  belongs.  It  is  evident 
that  the  first  great  purpose  to  be  accomplished  is  the  conferring 
of  the  powers  of  sensation  and  perception,  these  being  the  essen- 
tial attributes  of  animal  nature,  and  the  characteristics  which 
distinguish  it  from  the  mineral  or  vegetable  world.  Next  to 
these  is  the  power  of  voluntai^y  motion,  by  which  the  animal  is 
enabled  to  change  its  place,  to  procure  for  itself  those  objects 
which  are  necessary  for  its  subsistence  or  gratification,  and  to 
repel  those  which  are  noxious  or  painful. 

14.  The  power  of  being  affected  by  external  objects,  or  of 


GENERAL    VIEWS.  19 

receiving  impressions  of  which  we  are  conscious,  is  con- 
nected, in  the  more  perfect  animals,  with  a  part  of  the  body 
having  a  more  pecuhar  organization,  and  very  remarkable  pro- 
perties. It  is  a  soft  and  pulpy  substance,  of  a  whitish  colour,  with 
different  shades  of  gray,  opaque,  and  exhibiting  slight  traces  of 
a  fibrous  structure.  It  is  termed  medullary  or  nervous  substance. 
Of  this  substance  are  composed  the  hrain,  which  is  a  large 
mass  of  medullary  matter ;  and  also  the  nerves,  which  have  the 
appearance  of  white  cords,  extending  from  the  brain  to  almost 
every  other  part  of  the  body.  The  nerves  establish  a  communi-  • 
cation  between  these  parts  and  the  brain,  so  that  impressions 
made  upon  the  former,  are  communicated,  along  the  nerves,  and 
by  their  intermedium,  to  the  brain,  where  they  excite  their  appro- 
priate sensations,  corresponding  to  the  nature  of  the  impression, 
and  to  the  structure  of  the  organ  that  originally  received  it.  By 
what  agency,  or  in  what  way  affections  of  the  brain,  thus  in- 
duced, are  instrumental  in  producing  sensation,  or  how  the  sen- 
tient principle  is  connected  with  the  physical  constitution  of  the 
brain,  are  subjects  of  which  we  have  no  knowledge;  nor  have 
we,  in  our  present  state,  the  smallest  ground  of  hope  that  the 
mystery  in  which  it  is  involved,  will  ever  be  dispelled.  Sufficient 
let  it  be  for  us  that  such  is  the  fact ;  and  resting  on  this  as  an 
ultimate  fact,  let  us  proceed  in  our  inquiries,  as  to  the  occasions 
on  w^hich  this  power,  assuming  it  to  exist,  is  called  into  action. 

15.  Experience  shows  that  the  impressions  conveyed  by  each  . 
nerve,  or  class  of  nerves,  are  of  different  kinds,  for  they  are 
capable  of  being  readily  distinguished  from  one  another  by  the 
percipient  being  whose  brain  receives  them.  Hence  he  acquires 
a  knowledge  of  the  presence,  of  the  situation,  and  of  the  different 
properties  of  external  bodies,  which  are  the  source  of  those  im- 
pressions. The  nature  of  that  power  with  which  the  nerves  are 
endowed  is  such  as  to  convey  the  impressions  from  which  this 
knowledge  is  derived,  from  the  external  organ  to  the  brain,  with 
a  velocity  that  exceeds  all  imagination.  This  instantaneous 
transmission  is  evidently  a  provision  of  the  highest  importance 
both  for  the  welfare  and  preservation  of  the  individual. 

16.  The  different  powers  of  perception,  corresponding  to  dif- 
ferent qualities  of  external  objects,  constitute  the  external  senses; 
and  each  has  its  appropriate  organ,  furnished  with  its  separate 
system  of  nerves.  The  skin,  which  is  the  organ  of  touch,  receives 
the  largest  share  of  nerves,  as  it  is  evidently  of  the  greatest  con- 
sequence that  the  surface  of  the  body  should  receive  impressions 
from  every  substance  with  which  it  may  happen  to  come  in 
contact.  The  nerves,  of  the  skin  are  also  susceptible  of  various 
impressions,  besides  those  of  mere  impulse  or  resistance  from 
solid  bodies.  They  are  affected,  for  instance,  by  variations  of 
temperature ;  and  when  acted  upon  in  any  way  that  may  be  inju- 


20  PHYSIOLOGY. 

rious  to  the  part  impressed,  or  to  the  system  generally,  they  give 
suitable  warning  to  the  individual,  by  exciting  a  sense  of  pain. 
Hence  he  is  admonished  of  impending  evil,  and  is  incited  to  the 
prompt  adoption  of  the  means  of  averting  it. 

17.  Next  in  importance  to  the  sense  of  touch  are  those  of  sight 
and  oi  hearing ;  but  for  the  communication  of  distinct  impres- 
sions relating  to  these  senses,  a  much  more  refined  apparatus  is 
requisite  than  for  that  of  touch.  The  structure  of  the  eye  is 
calculated  to  combine,  upon  a  thin  expansion  of  nervous  sub- 
stance, the  retina,  the  rays  of  light  proceeding  from  distant 
objects,  so  as  to  form  a  picture  of  these  objects,  and  thus  convey 
to  the  mind  an  exact  knowledge  of  the  relative  situation  of  all 
their  parts  that  are  within  the  sphere  of  vision.  Hence  are 
derived  the  perceptions  of  their  distance  and  position  with  respect 
to  the  observer. 

18.  In  like  manner  are  the  sonorous  undulations  of  the  air  col- 
lected into  a  kind  of  focus  by  the  structure  of  the  ear,  and  im- 
pressed upon  the  sensitive  expansions  of  nervous  matter  in  the 
inner  regions  of  the  organ.  Thus  an  important  avenue  of  com- 
munication is  opened  with  the  external  world,  highly  useful  in  an 
infinite  variety  of  ways. 

19.  The  existence  and  properties  of  various  objects  at  a  dis- 
tance are  also  recognized  by  the  sense  of  Smell,  which  enables 
us  to  appreciate  the  presence  of  the  subtle  effluvia  which  they 
emit,  and  which  affect  thie  atmosphere  often  to  a  considerable 
distance  around.  The  olfactory  nerves  are  adapted  to  the  im- 
pressions of  this  kind,  and  are  situate  on  the  surface  of  those 
passages  destined  for  the  transmission  of  the  air  in  subservience 
to  another  function  hereafter  to  be  noticed,  namely,  that  of  respir- 
^ation. 

20.  The  sense  of  Taste  is  exercised  on '  the  substances  em- 
ployed as  aliment,  and  has  its' seat  at  the  entrance  of  the  passages 
appropriated  to  the  reception  of  food,  and  which  are  subservient 
to  another  class  of  functions  presently  to  be  described. 

21.  The  faculty  of  Sensation  consists  merely  in  the  excitation 
of  a  simple  mental  change,  known  to  every  one,  although  inca- 
pable, in  consequence  of  this  very  character  of  simplicity,  of 
either  analysis  or  definition-  With  reference  to  its  physiology, 
we  know  that  it  is  efiected  through  the  intermedium  of  certain 
nerves,  connected,  on  the  one  hand^  with  the  organs  on  which 
impressions  of  various  kinds  are  made  by  the  physical  action  of 
external  objects,  and  on  the  other,  with  those  parts  of  the  brain, 
of  which  the  physical  affections  are,  by  some  inscrutable  link, 
connected  with  the  affections  of  the  soul,  or  sentient  principle. 
These  simple  and  preliminary  phenomena,  composed  of  both 
physical  and  mental  changes,  are  to  be  carefully  distinguished 
from   those   subsequent  operations    that   constitute    perception. 


GENERAL    VIEWS.  21 

thoug"ht,  volition,  and  the  whole  series  of  psychical  phenomena, 
which  v^'e  are  in  the  habit  of  referring  to  a  distinct  branch  of 
human  knowledge,  and  which  is  generally  denominated  Meta- 
physics, Psychology,  or  the  Philosophy  of  Mind ;  in  contradis- 
tinction to  Physics,  Somatology,  or  the  Philosophy  of  Matter. 

2iJ.  There  can  be  little  doubt  that  these  operations,  which  we 
are  naturally  accustomed  to  consider  as  being  purely  of  a  mental 
character,  are,  in  some  unknown  degree,  connected  with  physical 
changes  taking  place  in  the  cerebral  substance ;  but  as  we  are 
utterly  unconscious  of  these  changes,  and  as  we  are  totally  pre- 
cluded from  arriving  at  any  knowledge  of  their  nature,  or  even 
of  conceiving  the  manner  in  which  a  connexion  between  mind 
and  matter  has  been  established,  we  are  compelled,  in  this  branch 
of  the  inquiry,  to  direct  our  attention  exclusively  to  the  mental 
phenomena,  to  study  their  laws  by  the  evidence  of  our  own  con- 
sciousness, and  to  resort  to  processes  of  analysis  and  methods  of 
inductive  investigation,  in  many  respects  different  from  those 
which  are  successfully  employed  in  the  more  arable  fields  of 
physical  science. 

Whenever  w'e  are  fortunate  enough  to  trace  some  portions  of 
the  mysterious  but  broken  thread  which  unites  the  material 
changes  occurring  in  our  bodily  organs,  with  the  operations  of 
the  intellect,  or  the  affections  of  the  soul,  we  may  then  occasion- 
ally re-enter  the  territory  of  Physiology ;  and  while  the  two 
sciences  are  thus  capable  of  being  studied  in  conjunction,  they 
will  derive  mutual  advantage  and  illumination. 

23.  Yet,  with  regard  to  the  mere  physiological  study  of  the 
animal  functions,  it  cannot  escape  our  observation,  that  a  vast 
variety  of  phenomena  in  the  economy  have  a  direct  reference  to 
the  mental  constitution  of  our  nature,  and  are  to  be  studied,  with 
relation  to  final  causes,  in  immediate  connexion  with  these 
objects.  Thus,  although  the  special  purposes  served  by  the  mul- 
tiplicity, the  curious  arrangement,  and  intricate  structure  of  the 
parts  of  the  brain,  are  as  yet  wholly  unknown,  and  we  still  are, 
and  shall  probably  ever  remain,  in  utter  darkness  as  to  the  mode 
in  which  they  perform  their  respective  ofiices  as  instruments  of 
perception,  thought,  and  volition,  yet  when  we  return  to  the 
observation  of  the  bodily  actions  consequent  on  these  mental  pro- 
cesses, as  well  as  contributing  to  their  performance,  we  are  ena- 
bled to  resume  our  physiological  inquiries,  and  trace  the  con- 
tinuity of  design  in  the  exercise  of  the  faculties  of  voluntary 
motion,  by  which  the  mind  exerts  a  power  of  reacting  on  matter, 
employs  its  properties  for  beneficial  ends,  and  exercises  that  par- 
tial dominion  over  nature,  which  has  been  granted  to  it  Ijy  the 
Divine  Author  of  its  being.  The  possession  of  voluntary  motion 
is  directed,  first,  to  enlarge  the  sphere  of  our  perceptions,  by 
directing  our  organs  of  sense  to  their  respective  objects ;  secondly. 


22  PHYSIOLOGY. 

to  bring  the  objects  themselves  within  the  reach  of  chose  organs 
by  which  they  are  to  be  exannined ;  thirdly,  to  alter  their  forms 
and  combinations,  and  modify  them  in  various  ways,  so  that  the 
mind  may,  from  these  different  modes  of  examination,  derive 
accurate  and  extensive  information  of  their  properties,  and  apply 
these  properties  to  use;  and  lastly,  to  effect  the  locomotion  of 
the  whole  body,  and  thus  extend  widely  the  range  of  its  opera- 
tions, and  spread  the  dominion  of  man  over  every  kingdom  of 
nature,  and  over  every  region  of  the  globe. 

24.  But  the  relations  of  man  with  the  external  world  compre- 
hend a  much  larger  and  more  important  field,  since  they  are  not 
limited  to  the  sphere  of  the  material  world,  but  embrace  the  in- 
tellectual and  moral  existence  of  other  percipient  and  sentient 
beings.  Through  the  intermedium  of  signs,  the  results  of  move- 
ments of  our  bodily  organs  acting  on  the  senses,  communications 
are  established,  not  merely  between  mind  and  matter,  but  be- 
tween mind  and  mind.  Mutual  interchanges  take  place,  of 
thoughts,  of  opinions,  of  feelings,  and  of  affections  ;  and  the  value 
of  existence  is,  to  an  incalculable  degree,  augmented  by  the 
operations  of  sympathy,  the  impulse  of  benevolence,  and  all  the 
potent  and  benign  influences  of  social^  union.  Hence,  physiolo- 
gically considered,  the  function  of  the  voice,  and  its  modulation 
into  articulate  sounds,  ranks  as  an  important  part  of  the  animal 
economy. 

25.  The  faculty  of  Voluntary  Motion,  like  that  of  Sensation, 
is  derived  from  the  peculiar  properties  of  the  nervous  substance. 
In  the  instance  of  sensation  impressions  are  conveyed  by  means 
of  the  nerves  from  the  external  organs  of  sense  to  the  general 
centre  of  the  sensitive  faculty,  the  brain.  A  similar  power,  we 
find,  is  exercised,  though  in  a  contrary  direction,  in  transmitting 
the  actions  arising  from  the  determinations  of  Volition,  and  which 
produce  the  first  effects  on  the  brain,  towards  those  parts  which 
are  capable  of  executing  these  determinations.  Modern  discove- 
ries have  shown,  that  for  this  latter  purpose  sets  c)f  nervous 
fibres  are  employed  different  from  those  instrumental  in  convey- 
ing sensitive  impressions  from  the  organ  of  sense  to  the  brain. 
Hence  a  distinction  is  established  between  the  Nerves  of  Sensa- 
tion, and  the  nerves  of  motion,  or  the  Motor  Nerves.^  While  the 
nerves  of  sensation  should  properly  be  considered  as  commencing 
at  the  organs  of  sense,  and  terminating  in  the  brain,  the  nerves 
subservient  to  volition  have  their  proper  origin  in  the  brain,  and 
proceed  thence  to  the  organs  of  motion.  Let  us  next  examine 
in  what  these  organs  of  motion  consist. 


*  We  would  suggest  the  propriety  of  designating  these  two  classes  of 
nerves  respectively,  by  the  terms  Sensiferous  and  Voluntiferous,  as  more  dis- 
tinctly expressing  their  proper  functions. 


GENERAL    VIEWS.  23 

26.  The  principal  source  of  motion,  in  the  animal  body,  resides 
in  the  Muscles^  which  taken  altogether,  usually  compose  by  far 
the  largest  part  of  the  bulk  of  the  animal.  Muscles  consist  of  a 
collection  of  fleshy  fibres,  proceeding  for  the  most  part  in  parallel 
directions,  and  extending  from  the  two  points  in  the  limb,  or 
parts  of  the  body,  which  are  designed  to  be  brought  nenrer  to 
each  other.  The  fibres  of  which  the  muscles  are  composed  are 
endowed  with  the  remarkable  property  of  contracting,  under 
certain  circumstances,  with  prodigious  power,  so  as  to  move  the 
parts  to  which  they  are  attached  with  sudden  and  enormous 
force.  The  impulse  given  to  them  by  the  nerves  of  volition,  by 
which  they  are  connected  with  the  brain,  in  every  effort  of 
volition,  excites  them  to  contraction,  antl  produces  those  move- 
ments of  the  body  which  are  the  objects  of  that  volition. 

27.  The  movements  required  for  the  purposes  of  animal  life, 
are  of  course  infinitely  diversified  in  their  kind,  and  scarcely 
admit  of  any  distinct  classification.  Amongst  the  objects  of 
these  movements,  however,  we  may  notice  two,  which  are  of 
essential  importance;  the  first  is  that  of  Locomotion,  the  second 
that  of  Prehension. 

28.  Locomotion  is  one  of  the  faculties  more  particularly  dis- 
tinctive of  animal  life  in  opposition  to  that  of  the  vegetable. 
Plants  are  more  or  less  rooted  to  the  soil  where  they  originally 
sprung:  animals,  destined  to  a  wider  sphere  of  action,  are  en- 
dowed wiih  the  power  of  transporting  their  bodies  from  place  to 
place,  on  the  one  hand,  of  pursuing,  and  on  the  other,  of  flying 
from  pursuit;  of  choosing  their  habitations,  or  of  changing  re- 
gions and  climes  according  to  their  wants  or  necessities.      • 

29.  The  power  of  detaining  and  laying  hold  of  olijects,  is 
another  mode  in  which  the  faculty  of  voluntary  motion  may  be 
highly  advantageous  to  the  animal  possessing  it.  With  these 
may  be  associated  the  various  actions  requisite  for  defence  or 
attack,  rendered  necessary  by  the  conflicts  incident  to  their 
condition. 

30.  For  the  performance  of  all  these  actions,  there  is  required, 
in  the  first  place,  a  solid  and  unyielding  structure,  capable  of 
sustaining  the  weight  of  the  body,  and  of  furnishing  to  the  mus- 
cles or  agents  of  motion,  fixed  points  of  attachment.  The  hones, 
the  union  of  which  constitutes  the  skeleton,  are  pr^ided  for 
these  objects.  They  are  formed  into  separate  pieces^  with  a 
view  to  their  being  moveable  upon  one  another.  Their  extre- 
mities are  connected  together  by  smooth  surfaces,  which  are 
bound  together  by  firm  bands  or  ligaments,  bracing  them  on  the 
sides  where  they  are  exposed  to  the  greatest  strain.  An  appa- 
ratus of  this  kind  constitutes  ^  joint. 

31.  The  due  performance  of  these  mechanical  objects,  implies 
a  variety  of  subsidiary  contrivances  and  adjustments,  too  diver- 


24  PHTSIOLOGr. 

sified  in  their  nature  and  objects  to  admit  of  particular  specifica- 
tion. It  is  evident  that  the  particular  texture  of  each  part  must 
be  adapted  to  the  action  it  has  to  perform.  Flexibihty  and  com- 
pressibiUty  are  required  in  one  organ ;  rigidity  and  hardness  in 
another.  Some  parts  must  readily  yield  to  an  extending  force, 
others  must  resist  such  a  force  with  extraordinary  tenacity. 
Some  must  exert  elastic  power,  others  must  be  devoid  of  this 
quality.  Some  textures  must  be  permeable  to  fluids,  others  must 
deny  them  all  transmission.  Hence,  the  variety  of  structures 
composing  the  mechanical  frame-work  of  the  system. 

32.  But  in  all  the  variations  of  conformation,  it  would  appear 
that  nature  has  employed  the  same  ultimate  structure  as  the^ 
basis  of  her  work.  All  the  soHd  parts  of  the  animal  fabric  are 
formed  of  fibres,  variously  united  and  interwoven ;  in  some  cases 
only  loosely  connected,  so  as  to  constitute  a  spongy  or  cellular 
mass,  flexible  in  every  direction,  and  forming  a  medium  of  con- 
nexion between  adjacent  parts  of  various  degrees  of  cohesion. 
This  substance,  which  is  found  universally  to  pervade  the  body, 
is  termed  the  cellular  substance  or  texture.  It  is  eminently  en- 
dowed with  elasticity,  and  thus  contributes  essentially  to  preserve 
the  natural  figure  of  every  organ,  and  to  restore  it  to  its  proper 
situation,  after  any  displacement  by  a  foreign  cause. 

33.  When  condensed  into  a  firmer  layer  or  sheet  of  animal 
matter,  the  same  substance  assumes  the  form  of  Jiiemhrane,  and 
is  extensively  employed  as  such,  to  supply  organs  with  external 
coverings,  or  to  afibrd  them  attachments  to  surrounding  parts  for 
the  purpose  of  protection  and  support.  Membranes  are  also 
used  as  barriers,  for  intercepting  the  communication  of  fluid  from 
one  cavity  to  another;  and  they  are  also  employed  to  form 
receptacles  for  the  retention  of  fluids,  arid  tubes  for  conveying 
them  from  one  part  of  the  system  to  another. 

34.  The  fibrous  structures,  comprehending  ligaments,  tendons, 
fascice,  are  composed  of  a  still  denser  approximation  of  fibres, 
are  endowed  with  a  higher  degree  of  toughness  and  strength, 
and  are  capable  of  exerting  great  resistance  to  any  stretching 
force.  Hence,  they  are  extensively  employed  in  the  construction 
of  parts  where  these  properties  are  required. 

35.  The  organs  specially  appropriated  to  touch,  are  generally 
also  thoi^  of  prehension :  and  progressive  motion  is  accom- 
plished by  means  of  limbs,  which  act  either  upon  the  ground,  the 
waters,  or  the  air,  according  to  the  element  in  which  the  animal 

'  resides.  'But,  in  order  to  give  proper  effect  to  these  movements, 
the  agency  of  levers  is  required;  and  we  accordingly  find  a  pro- 
vision made  for  this  purpose  in  the  construction  of  the  bones, 
which,  as  we  have  before  observed,  are  capable  of  supplying  the 
fulcra  or  fixed  centres  of  motion,  and  allow  of  the  application  of 
the  moving  powers.     It  often  happens  that  the  actual  attachment 


GENERAL    VIEWS.  25 

of  muscles  to  the  point  required  to  be  moved,  would  be  attended 
with  inconvenience.  In  this  case,  an  intermediate  structure  is 
employed,  analagous  to  that  of  a  ligament,  but  here  denominated 
a  tendon,  serving  as  a  strap  to  connect  the  muscle  to  a  distant 
bone,  or  other  part  on  which  the  action  of  the  muscle  is  to  be 
exerted. 

30.  All  the  functions,  which  have  for  their  object  some  mechan- 
ical effort  of  the  kind  we  have  now  described,  may  be  compre- 
hended under  the  general  head  of  the  mechanical  functions. 

37.  The  consideration  of  the  chemical  condition  of  the  animal 
system,  introduces  us  to  a  class  of  functions  of  a  totally  different 
nature  from  any  of  the  preceding,  yet  equally  essential  to  the 
maintenance  of  life.  The  solids  and  fluids  of  which  organized 
structures  are  composed,  differ  materially  in  their  chemical  con- 
stitution from  the  products  of  the  mineral  kingdom.  Their 
elements  are  combined  by  a  much  more  complicated  arrange- 
ment, and  united  by  less  powerful  affinities  ;  or  rather  the  balance 
of  affinities,  by  which  they  are  held  together,  is  more  easily 
destroyed,  and  thus,  proneness  to  decomposition  is  constantly 
present.  One  of  the  most  remarkable  and  important  of  the 
operations  of  the  vital  functions,  is  to  repress  this  tendency  to 
decomposition ;  for  no  sooner  is  life  extinct,  than  we  find  both  the 
solids  and  fluids  of  the  body  hastening  to  assume  new  forms  and 
combinations  of  their  elements  ;  and  nothing  can  now  prevent  the 
final  disorganization  of  that  fabric  which  so  lately  delighted  the 
eye  with  its  beauty,  and  in  which  dwelt  the  genial  warmth  of 
fife,  and  the  elastic  vigor  of  youth.  If  we  watch  the  progress  of 
those  dangers  which  take  place  in  the  body,  we  shall  find  it 
characterised  by  a  perpetual  renovation  of  materials,  continual 
losses  of  substance  on  the  one  part,  being  compensated  by  an 
equally  constant  supply  on  the  other.  From  an  atom  of  imper- 
ceptible minuteness  we  trace  its  gradual  increase  of  size,  by  the 
reception  of  nutritious  matter  from  without,  by  the  incorporation 
of  this  matter  with  that  which  had  before  existed,  by  the  conso- 
lidation of  the  fluid,  by  th^  extension  of  the  solid  parts.  We  see 
all  the  organs  expanding  by  a  slow,  but  uniform  increase,  and  in 
regular  proportion,  till  they  arrive  at  a  certain  limit.  Having 
attained  this  limit,  the  body  remains  stationary  for  a  certain 
period ;  that  is,  the  waste  of  substance  is  exactly  compensated  by 
the  supplies  furnished  by  the  food  received  into  the  body.  At 
length,  however,  the  compensation  is  less  perfectly  maintained ; 
the  powers  which  carry  on  the  functions  begin  to  decline,  the 
solids  dry  up  and  harden,  and  a  general  torpor  gradually  pervades 
the  system.  Life  is  sooner  or  later  brought  to  a  close  by  the 
natural  progress  of  these  changes,  even  if  its  course  be  not  sooner 
arrested  by  causes  of  an  accidental  nature. 

38.  The  functions  of  nutrition  embrace  a  class  of  operations, 

3 


26  '  PHYSIOLOGY. 

destined  to  supply  the  materials  wanted  for  the  growth  of  the 
body,  and  for  the  supply  of  those  materials  which  either  may 
have  been  expended  in  the  natural  exercise  of  the  other  functions, 
or  lost  in  various  ways,  or  else  employed  in  the  reparation  of 
injuries,  which  the  organs  may  have  accidentally  sustained.  The 
nutritive,  or  as  they  may  also  be  termed  the  chemical  functions, 
since  they  relate  to  the  chemical  condition  of  the  body,  compre- 
hend a  long  series  of  processes,  which,  in  order  to  be  studied 
successfully,  require  many  successive  subdivisions. 

The  first  division  includes  all  those  functions  which  contribute 
to  the  reduction  of  the  food  to  a  substance  of  similar  chemical 
composition  with  the  materials  of  which  the  body  already  con- 
sists ;  pi'ocesses  which  are  comprehended  under  the  general  term 
of  Assimilation. 

The  second  and  third  divisions  relate  to  the  collection  of  the 
nutriment  thus  prepared,  or  assimilated,  into  a  general  reservoir; 
and  its  subsequent  distribution  throughout  the  body,  so  as  to 
admit  of  being  applied  to  use  whenever  it  may  be  wanted.  These 
objects  are  attained  by  the  functions  of  Absorption  and  of  Circu- 
lation. 

A  fourth  division  refers  to  the  purification  of  the  general  mass 
of  nutritious  fluid  existing  in  the  great  reservoir  of  the  body,  by 
the  separation  of  its  superfluous  combustible  portion,  and  more 
especially  of  its  carbon  ;  a  change  which  is  effected  by  the  func- 
tion of  Respiration. 

The  last  division  of  this  class  of  functions  comprehends  the 
several  processes  by  which  certain  materials  are  separated  from 
the  blood  in  a  solid  or  fluid  form ;  some  wdth  a  view  to  their 
final  expulsion  from  the  system,  some  to  answer  purposes  con- 
nected with  other  functions,  and  the  remaining  part  being 
expended  in  repairing  the  waste  which  the  solids  of  the  body 
undergo  in  the  exercise  of  their  respective  offices.  To  the  former 
of  these  functions  the  term  Secretion  is  applied:  whilst  the  last 
is  more  especially  regarded  as  the  proper  and  final  process  of 
Nutrition,,  We  shall  examine  each  of  these  divisions  more  par- 
ticularly. 

39.  Assimilation  is  effected  by  a  long  series  of  processes,  which 
are  partly  of  a  mechanical  and  partly  of  a  chemical  nature.  The 
food  taken  into  the  mouth  is  first  masticated  by  the  action  of  the 
teeth  and  jaws,  so  as  to  break  down  the  cohesion  of  its  parts,  and 
prepare  it  for  the  chemical  action  of  the  fluids  to  which  it  is  after- 
wards to  be  subjected.  There  is  at  the  same  time  added  to  it  a 
quantity  of  liquid,  termed  the  saliva,  prepared  by  a  set  of  glands, 
to  be  hereafter  specified,  and  poured  out  into  the  mouth  in  large 
quantities  during  the  act  of  mastication.  By  these  means  the 
food  is  softened  in  its  texture,  and  reduced  to  the  form  of  a  pulp, 
in  which  state  it  is  swallowed,  by  the  organs  of  deglutition,  and 


GENERAL    VIEWS.^  27 

conveyed  through  a  tube  called  the  cesophagus  into  the  stomach. 
The  stomach  is  a  capacious  bag,  or  receptacle,  capable  of  holding 
a  considerable  quantity  of  food,  and  of  retaining  it  for  a  certain 
period.  The  inner  niembrane  which  lines  the  cavity  of  the 
stomach  prepares  a  fluid  termed  the  gastric  juice,  w^hich  acts 
chemically  upon  the  food  in  that  cavity,  while  this  food  is  at  the 
same  time  subjected  to  a  degree  of  pressure  from  the  action  of  a 
set  of  muscular  fibres  which  are  interposed  between  the  interior 
and  exterior  coats  of  the  stomach.  The  food  is  also  slowly 
moved  by  the  successive  contractions  of  these  muscles,  so  that 
every  part  of  it  comes  in  its  turn  to  be  acted  upon  by  the  gastric 
juice,  until  the  whole  is  converted  into  a  soft  and  smooth  mass  of 
uniform  consistence  which  is  termed  chij?ne ;  the  operation  itself 
by  which  this  conversion  is  effected  being  termed  digestion. 

40.  The  aliment  thus  digested,  or  reduced  to  the  state  of  chyme, 
passes  onwards  from  an  orifice  at  the  farther  end  of  the  stomach 
into  a  tube  of  great  length,  several^ portions  of  which  have  received 
different  names,  but  which  are  comprised  under  the  general  term 
of  the  intestines.  In  the  first  portion,  the  duodenum,  the  aliment 
undergoes  still  further  changes  ;  it  is  mixed  with  two  fluids,  the 
one  called  the  bile,  which  is  prepared  by  a  large  glandular  organ, 
termed  the  liver  ;  and  the  other  called  i\\Q  pancreatic  juice,  pre- 
pared by  another  gland,  the  pa7icreas.  Secretions  also  take 
place  from  the  inner  membrane  of  the  intestines  themselves,  and 
the  result  of  the  united  action  of  all  these  fluids,  aided  by  the 
movements  imparted  to  the  aliment  by  the  contractions  of  the 
muscular  fibres  contained  in  the  coats  of  the  intestines,  is  gradu- 
ally to  convert  part  of  what  was  chyme  into  a  new  substance 
called  chyle,  which  is  the  most  nutritious  portion  of  the  aliment, 
and  has  the  appearance  of  a  milky  fluid.  The  chyle  is  received 
into  a  set  of  very  minute  tubes  called  lacteals,  which  are  ex- 
ceedingly numerous,  and  arise  by  open  mouths  from  the  inner 
surface  of  the  duodpnum  and  its  prolongations,  the  jejunum  and 
ileum.  They  collect  the  chyle  together,  and  pour  it  into  an 
intermediate  receptacle,  whence  it  is  conveyed  along  a  large  tube 
called  the  thoracic  duct,  into  other  cavities,  of  which  we  shall 
presently  speak.  That  portion  of  the  chyme  which  is  not  con- 
verted hito  chyle,  descends  into  the  lower  portions  of  the  intestinal 
canal,  is  collected  in  the  larger  intestines,  of  which  the  colon  is 
the  principal  one,  and  is  finally  6jected  from  the  body. 
,  41.  The  next  step  in  the  assimilatory  process  is  the  conversion 
of  the  chyle  into  blood,  a  change  which  has  been  termed  sangui- 
fication. It  is  in  the  great  system  of  vessels  which  contained 
the  blood  already  formed,  and  in  the  course  of  the  passages  through 
which  the  blood  is  moved,  that  this  gradual  change  is  effected. 
The  great  reservoir  of  this  important  fluid,  on  which  the  nutri- 
tion of  every  part  of  the  body,  and  its  maintenance  in  a  state  of 


28  PHYSIOLOGY. 

action,  immediately  depend,  is  the  heart.  The  thoracic  duct 
opens  into  one  of  the  veins  or  tubes  leading  directly  to  the  heart ; 
the  chyle  is  therefore  immediately  conducted  into  this  reservoir, 
and  thoroughly  mixed  with  the  general  mass  of  food. 

42.  The  heart  is  a  powerful  muscular  organ ;  from  its  cavity 
arise  the  trunks  of  large  tubes,  called  arteries,  which  subdivide 
and  ramify  as  they  proceed  in  their  course  to  every  part  of  the 
body,  being  distributed  in  abundance  to  every  organ,  with  a  very 
few  exceptions.  No  sooner  are  the  cavities  of  the  heart  distended 
with  blood,  than  the  muscular  structure  which  surrounds  their 
cavities  contracts  with  enormous  force,  and  propels  their  fluid 
contents  through  the  system  of  arteries,  sending  it  in  one  great 
wave,  even  to  the  extremities  of  its  minutest  ramifications.  From 
these  extremities  of  the  arteries  it  passes  into  corresponding 
branches  of  another  set  of  vessels,  the  veins,  which  proceed  in 
the  opposite  direction,  towards  the  heart,  uniting  in  their  course 
into  larger  and  larger  trunks,  till  they  reach  the  heart,  to  which 
they  deliver  back  the  portion  of  blood  that  has  thus  percolated 
through  every  part  of  the  body.  No  sooner  has  it  again  filled 
the  cavities  of  the  heart,  than  it  is  again  sent  with  renewed  force 
into  the  same  arterial  channels,  and  again  brought  back  by  the 
veins.  The  functions  by  which  this  circular  course  is  given  to 
the  blood,  is  termed  the  circulation. 

43.  The  blood,  in  the  course  of  its  circulation,  furnishes  to  all 
the  organs  the  materials  which  are  necessary  for  their  growth, 
for  the  renovation  of  their  powers,  and  for  the  supply  of  those 
iiuids  and  other  animal  products  which  are  wanted  in  various 
parts  of  the  economy.  The  separation  of  these  fluids,  and  the 
formation  of  these  peculiar  animal  products,  are  the  objects  of 
another  function,  that  of  secretion.  Particular  organs  are  in 
most  cases  provided  for  the  purpose  of  eflfecting  these  processes. 
These^are  the  glands,  which  are  variously  constructed,  according 
to  the  particular  offices  they  have  to  perform  ;  each  is  furnished 
with  an  elaborate  apparatus  pf  vessels ;  and  the  fluid  which  is 
formed  by  them,  is  generally  conducted  to  its  place  of  destination 
by  a  pipe,  or  excretor^y  duct,  as  it  is  termed. 

44.  The  fluids  which  are  thus  separated  from  the  blood  are, 
for  the  most  part,' applied  to  useful  purposes  in  different  parts  of 
the  economy;  some  for  the  repair  of  that  loss  of  substance  in 
the  part  of  the  body  incident  to  the  exercise  of  their  respective 
functions,  others  for  different  subsidiary  purposes  related  to  those 
functions.  The  substance  of  the  bones,  for  example,  undergoes 
a  gradual  change  during  the  whole  of  life  ;  each  particle  is  re- 
moved in  succession  and  is  replaced  by  others,  so  that  iii  the 
course  of  time  the  whole  substance  of  the  body  undergoes  reno- 
vation. Two  important  functions  are  called  into  action  for  the 
completion  of  these  processes  ;  the  first  of  these  is  concerned  in 


GENERAL    VIEWS. 


d9 


the  removal  of  the  old  and  decayed  materials ;  the  second  in  the 
due  application  of  those  which  are  to  replace  them. 

45.  The  removal  of  those  particles  which  have  become  useless, 
and  W'hose  presence  might  be  injurious,  is  effected  by  a  distinct 
set  of  vessels,  called  lymphatics.  The  lymphatics  are  met  with 
in  almost  every  part  of  the  body  ;  and  resemble,  both  in  structure 
and  mode  of  distribution,  the  lacteal  vessels  already  described. 
The  mode  of  their  origin  is  not  well  ascertained,  but,  like  the 
lacteals,  the  smaller  branches  successively  unite  into  trunks, 
which  terminate  either  in  the  thoracic  duct,  or  into  the  larger 
veins  leading  directly  to  the  heart.  Through  these  channels, 
then,  it  is  that  all  the  particles  which  require  removal  are  con- 
veyed away,  and  deposited  in  the  general  mass  of  circulating 
fluids.  The  function  thus  performed  by  the  lymphatics  in  com- 
mon with  the  lacteals,  is  termed  absorption.* 

46.  The  function  having  for  its  object  the  reparation  of  the 
substance  of  the  different  organs,  is  designated  by  the  general 
name  Nutrition.  It  includes  the  development  and  growth  of 
the  parts,  and  their  maintenance  in  the  healthy  state, — that  is, 
the  state  in  which  they  are  fitted  for  the  exercise  of  their  several 
functions ;  as  well  as  the  restoration  of  what  they  may  have  lost 
from  accidental  causes,  such  as  mechanical  injuries. 

When  a  bone  is  broken,  for  instance,  a  solid  union  is  by  de- 
grees effected  by  the  deposit  of  new  ossific  materials,  consisting 
chiefly  of  phosphate  of  lime,  which  is  secreted  or  separated  from 
the  blood  by  the  irritated  vessels  in  the  neighbourhood  of  the 
injury.  In  all  these  cases,  the  absorbents  are  also  at  work  in 
modelling  the  shape  of  the  part  to  be  restored,  in  removing  all 
roughnesses  or  angular  projections,  and  making  room  for  the 
new  formations  which  are  to  take  place.  The  functions  of  ab- 
sorption and  nutrition  are  thus,  in  some  respects,  opposed  to  each 
other,  producing  contrary  effects,  though  both  co-operating  in 
the  accomplishment  of  one  final  purpose,  and  balanced  and  ad- 
justed to  one  another  with  that  manifest  intention.  The  general 
bulk  of  the  body,  and  of  its  parts,  varies  according  to  the  predo- 
minance of  the  one  or  the  other  of  these  actions  of  absorption 
and  nutrition;  wasting  when  the  former  is  in  excess;  thriving 
and  enlarging  when  the  latter  prevails. 

47.  There  is  one  peculiar  mode  in  which  superabundant  nutri- 
tion manifests  itself  When  the  supply  of  nutriment  is  greater 
than  what  the  wants  of  the  system  require,  the  superfluous  por- 
tion is  converted  into  an  oily  fluid,  which  is  laid  up  in  store  for 
future  use.    The  fluid  is  the/<2^ ;  and  it  is  accumulated  in  various 

*  [Absorption  is  not,  however,  effected  exclusively  by  the  lymphatics.  It 
will  be  seen,  hereafter  (549),  that  when  substances  possess  the  necessary 
tenuity,  they  readily  pass  through  the  parietes  of  the  veins  under  favourable 
circumstances,  and  enter  the  circulation.] 

'A* 


30  PHYSIOLOGY. 

parts  of  the  body,  and  especially  between  the  skin  and  the  mus- 
cles, and  in  other  places,  where  it  may  also  serve  a  subsidiary 
purpose  of  mechanical  protection  against  inequalities  of  pressure. 
The  fat  is  thus  useful  as  a  soft  cushion  on  which  deUcate  organs, 
such  as  the  eye,  may  move  in  security ;,  and  also  as  a  convenient 
material  for  filling  up  hollows  in  various  unoccupied  situations. 
The  chief  use,  however,  of  large  accumulations  of  fat,  is  to  serve 
as  a  magazine  ,pf  nutriment,  out  of  which  the  body  may  be  sup- 
ported in  those  seasons  when  the  supply  of  food  is  deficient,  and 
more  particularly  du)i-ing  those  periods  which  are,  by  some  ani- 
mals, passed  in  a  state  of  complete  inactivity.  This  is  the  case 
in  those  animals  which  are  said  to  hyhernate,  or  continue  during 
the  whole  of  winter  in  a  perfectly  torpid  state. 

48.  Whilst  some  of  the  products  of  secretion  are  thus  employed 
in  nutrition,  others  are  subservient  to  the  functions  of  particular 
organs.  Thus,  the  tears  are  useful  in  washing  away  from  the 
surface  of  the  eye,  dust,  and  other  materials  which  might  obstruct 
vision ;  the  gastric  juice  is  subservient  to  digestion ;  and  the 
mucilaginous  secretion  of  the  wind-pipe  and  nostrils  defend  those 
passages  from  the  acrimony  of  the  air.  But,  in  other,  cases,  the 
secreted  matters  have  noxious  qualities ;  and  it  is  the  object  of 
their  separation  from  the  blood,  to  get  rid  of  them  altogether. 
This  is  the  case  with  the  secretions  from  the  kidneys,  and  from 
the  skin,  and  perhaps,  also,  partly  with  that  from  the  liver. 
These  are  termed  the  excretions,  in  contradistinction  to  the  pro- 
per secretions,  and  the  organs  which  separate  them  are  termed 
the  emunctories. 

49.  The  organs  which,  in  this  sense  of  the  term,  must  be  con- 
sidered as  the  principal  emunctory  of  the  body  are  the  lungs.  It 
would  appear  that  the  blood,  from  which  the  animal  solids  and 
fluids  derive  their  nourishment,  contains  a  larger  proportion  of 
carbon  than  what  is  required  for  the  formation  and  reparation  of 
these  soHds  and  flyids ;  the  elements  abstracted  from  the  blood 
by  the  process  of  secretion  and  nutrition,  being  principally  oxy- 
gen, hydrogen,  and  nitrogen.  \ 

The  continuance  of  these  processes  must  tend,  therefore,  to 
produce  an  accumulation  of  carbon  in  the  blood ;  and  accord- 
ingly we  find. that  this  fluid,  in  the  course  of  its  circulation,  gra- 
dually acquires  a  darker  colour.  From  being  of  a  vivid  scarlet 
hue  in  the  trunks  of  the  arteries,  it  has  changed  to  a  dark  purple 
by  the  time  it  has  reached  the  veins.  It  is  returned  to  the  heart, 
therefore,  in  a  state  unfit  for  the  purposes  of  nutrition,  and  not 
proper  to  be  again  circulated  through  the  vessels  of  the  body. 
In  order  to  restore  it  to  its  original  state,  it  is  necessary  to  de- 
prive it  of  the  ingredient  it  contains  in  excess,  that  is,  of  carbon, 
which,  when  thus  present  in  the  blood,  is  found  to  exert  a  posi- 
tively deleterious  power  on  the  parts  to  which  it  is  applied. 


GENERAL   VIEWS.  31 

For  this  purpose  the  blood  is  transmitted  by  an  appropriate 
system  of  arteries,  to  the  lungs,  where  it  is  exposed  to  the  influ- 
ence of  atmospheric  air,  alternately  received  into,  and  expelled 
•from  that  organ.  By  a  process  which  appears  to  be  analogous 
to  slow  combustion,  the  superfluous  carbon  of  the  blood  combines 
with  the  oxygen  of  the  atmospheric  air,  and  is  expelled,  in  the 
form  of  carbonic  acid  gas,  along  with  the  air  expired.  The  blood 
thus  purified,  and  restored  to  its  salutary  qualities,  is  conducted 
back  again,  by  a  corresponding  set  of  veins,  to  the  heart,  and  is 
again  sent,  by  the  contractions  of  that  organ,  into  the  arteries  of, 
the  body,  and  performs  the  same  round  of  circulation  as  before. 
Respiration,  which  is  the  title  of  the  function  we  have  now  been 
describing,  completes  this  class,  which  we  have  termed  the  che- 
mical functions  of  the  economy. 

50.  The  three  classes  of  functions  we  have  been  reviewing, 
namely,  the  mechanical,  the  chemical,  and  the  sensitive,  relate 
only  to  the  preservation  and  welfare  of  the  individual.  But  as 
nature  has  assigned  a  limit  to  the  duration  of  Hfe,  it  became  ne- 
cessary that  a  provision  should  be  made  for  the  multiplication  of 
individuals,  and  the  conservation  of  the  race.  Such,  then,  is  the 
object  of  a  fourth  class  of  functions,  namely  the  reproductive 
functions,  including  the  process  oi  fecundation,  of  evolution,  of 
gestation,  and  of  parturition,  and  the  auxiliary  function  of 
lactation,  provided  for  the  supply  of  the  new-born  infant  with 
nourishment  adapted  to  the  tender  condition  of  its  organs  of 
assimilation. 

51.  Having  studied  the  phenomena  and  the  circumstances 
which  lay  the  foundations  of  individual  existence,  the  physiologist 
has  next  to  occupy  himself  with  the  consideration  of  the  long 
series  of  changes  which  intervene  between  the  cradle  and  the 
grave,  and  constitute  the  "  strange  eventful  history"  of  the  phy- 
sical life  of  man.  He  follows  the  rise  and  development  of  the 
several  organs,  and  the  occasions  on  which  their  functions  are 
called  forth :  he  notices  their  entry  on  the  stage  of  life,  in  which 
they  are  destined  to  play  more  or  less  important  parts;  he 
watches  their  progress,  maturity,  and  decay,  till  they  finally 
disappear  from  the  scene,  when  their  functions  have  successively 
declinfed,  and  passed  away,  the  vital  spark  becomes  extinguished, 
and  the  curtain  drops  on  the  fleeting  drama  of  our  probationary 
existence.  A  multitude  of  interesting  subjects  press  on  his  atten- 
tion in  tjiis  division  of  his  subject,  so  replete  with  wonder,  and 
so  calculated  to  impress  us  with  exalted  ideas  of  divine  presci- 
ence, and  of  the  unbounded  resources  of  creative  power. 

To  this  department  of  physiology  properly  belong,  first,  the 
history  of  the  changes  which  take  place  in  the  organs,  during 
their  natural  course  of  development,  in  what  has  been  styled 
their  normal  condition,  such  as  the  formation  of  the  vital  organs, 


32  PHYSIOLOGT. 

the  process  of  ossification,  the  general  growth  of  the  body,  the 
changes  occurring  at  the  period  of  puberty,  the  slow  but  sure 
progress  of  consolidation  attending  the  decline  of  life,  and  the 
successive  decay  and  obliteration  of  the  faculties  which  precede 
death ;  and,  secondly,  the  study  of  phenomena  exhibiting  the 
operation  of  those  powers  of  repair  and  renovation,  which  exist 
in  the  constitution,  and  which  are  called  forth  only  on  certain 
occasions,  when  the  organization  has  been  injured  or  destroyed, 
or  when  the  functions  have  been  deranged  or  suspended,  by 
various  accidental  causes. 

52.  These  topics  introduce  to  our  notice  the  varieties  which 
are  observable  in  different  classes  of  individuals  in  the  general 
mode  in  which  the  functions  are  performed  with  reference  to 
their  balance,  or  relative  preponderance :  conditions  which  con- 
stitute the  different  temperaments,  as  they  are  called,  and  which 
are  severally  characterised  by  peculiar  external  indications. 

53.  Physiology,  lastly,  comprehends  within  the  scope  of  its 
inquiries,  those  more  strongly  marked  diversities  that  are  met 
with  in  the  inhabitants  of  different  regions  of  the  globe,  and 
which  appear  to  form  separate  races  of  mankind.  These  con- 
stitutional peculiarities,  as  shown  by  diffei-ences  both  in  external 
conformation,  and  in  the  internal  endowments  of  an  intellectual 
and  moral  nature,  are  of  so  distinct  and  permanent  a  character, 
as  to  have  suggested  the  hypothesis;,  of  their  indicating,  in  a 
zoological  sense,  not  merely  varieties  of  a  single  species,  but 
several  different  species  of  the  genus  Man. 

54.  The  present  treatise  is  intended  to  exhibit  a  condensed 
viqw  of  the  actual  state  of  our  knowledge  on  all  the  subjects  com- 
prised in  the  above  outline,  and  to  conclude  with  a  review  of  the 
progressive  history  of  the  science  from  the  earliest  periods  to  the 
present  time. 

55.  It  is  hardly  necessary  to  remark,  that  the  province  of 
Physiology,  is  restricted  to  the  consideration  of  the  phenomena 
of  the  living  body  in  its  perfectly  normal  or  healthy  state:  while 
those  which  are  presented  when  these  hmits  of  healthy  action 
are  passed,  and  when  the  abnormal,  or  diseased  state  commences, 
are  the  subjects  of  another  branch  of  science,  denominated  Pa- 
thology, no  less  interesting  and  important  than  the  former,  as 
furnishing  the  principles  by  which  the  art  of  medicine  derives  all 
its  powers;  but  which,  it  must  be  obvious,  must  have  its  founda- 
tions laid  in  an  extensive  and  correct  knowledge  oi physiology. 

56.  It  is  evident  that  the  foundation  of  all  physiological  know- 
ledge must  be  laid  in  a  thorough  acquaintance  with  the  structure 
or  internal  mechanism  of  animals.  The  study  of  anatomy, 
indeed,  derives  its  chief  interest  from  its  connexion  with  physi- 
ology ;  for  unless  viewed  with  reference  to  their  uses  or  sub- 
serviency to  particular  purposes,  the  examination  of  the  forms 


GENERAL    VIEWS.  ,  33 

and  properties  of  the  parts  of  a  machine  would  be  a  barren  and 
an  irksome  task.  Let  us  imagine,  for  example,  a  person,  who 
had  never  seen  a  ship,  and  had  no  idea  of  the  object  for  which  it 
is  intended,  to  visit  it  for  the  first  time,  and  to  be  at  liberty  to 
examine  at  his  leisure  every  part  of  its  rigging  and  internal  con- 
struction. A  restless  curiosity  might  indeed  lead  him  to  handle 
the  ropes  and  blocks,  and  climb  upon  every  mast ;  to  descend 
between  the  decks,  and  minutely  inspect  every  part  of  its  fabric ; 
to  explore,  in  a  word,  the  whole  anatomy  of  this  most  stupendous 
product  of  human  ingenuity.  But  his  labour  would  avail  him 
nothing.  The  most  complete  survey  would  afford  him  no 
instruction,  or  leave  any  distinct  impression  as  long  as  he  had  no 
principle  to  connect  them  in  his  mind.  But  let  him  review  the 
same  objects  with  an  experienced  guide,  instructing  him,  as  he 
proceeds,  on  the  general  purposes  of  the  whole  machine,  and  the 
particular  uses  of  every  part,  as  well  as  on  the  mode  in  which 
they  operate  and  concur  in  the  production  of  the  intended  effect. 
Then  it  is  that  he  will  feel  a  real  interest  in  the  examination : 
then  it  is  that  he  will  attach  due  importance  to  each  part  of  the 
inquiry.  Perceiving  the  relations  which  connect  the  objects,  and 
understanding  the  functions  of  the- several  instruments  he  sees,  he 
is  no  longer  perplexed  and  bewildered ;  individual  facts  arrange 
themselves  in  a  natural  order,  and  the  whole  forms  in  his  mind 
one  connected  system  of  knowledge,  readily  retained  and  easily 
communicated. 

The  case  is  perfectly  similar  with  regard  to  the  body  of  an 
animal,  of  which  anatomy  lays  open  to  us  the  structure.  Dissec- 
tion can  only  show  us  that  it  consists  of  various  parts,  some 
hard,  some  soft,  and  others  fiuid.  The  harder  parts,  such  as  the 
bones,  are  of  various  forms,  perforated  by  numerous  apertures, 
and  joined  together  in  different  ways.  The  soft  parts  are  found 
to  be  composed  of  various  kinds  of  textures,  of  which  the  ele- 
ments appear  to  be  collections  of  fibres  or  plates,  curiously  dis- 
posed and  interwoven,  so  as  to  constitute  a  cellular  or  spongy 
tissue,  and,  occasionally,  more  extended  layers  of  membrane. 
In  every  part  we  find  innumerable  tubes  and  passages  branching 
out,  and  again  uniting,  in  an  infinite  variety  of  ways.  We  arrive 
at  cavities  of  different  forms  and  extent,  enclosing  organs  of 
various 'descriptions,  or  containing  fluids  which  pass  through 
appropriate  channels  of  communication  to  very  distant  parts  ; 
composing  altogether  a  vast  and  complicated  system  of  mechani- 
cal and  hydraulic  apparatus.  Thus,,  whilst  we  confine  our  atten- 
tion to  the  mere  anatomy,  all  is  perplexity  and  confusion  ;  we 
are  overwhelmed  by  the  multiplicity  of  objects,  and  lost  in  the 
immense,  mass  of  unconnected  detail.  But  no  sooner  do  we  study 
the  parts  of  the  animal  frame  with  reference  to  their  uses,  and 
their  subserviency  to  the  several  functions  of  the  living  body, 


34  PHYSIOLOGY.  , 

than  the  whole  appears  under  a  new  aspect.  Aided  by  the  Hght 
of  physiology,  we  trace  order  and  connexion  in  every  part,  and 
gather  increasing  delight  and  instruction  as  we  proceed.  The 
requisite  adaptation  of  the  organs  to  their  respective  offices,  and 
the  correspondence  established  between  these  offices,  by  which 
they  concur  in  the  same  ultimate  object,  must  ever  excite  our 
most  profound  admiration,  and  exalt  our  ideas  of  that  infinite 
intelligence  which  planned,  and  that  transcendent  power  and 
beneficence  which  executed  the  vast  and  magnificent  system  of 
creation. 


CHAPTER  II. 


APPLICATIONS     OF     PHYSIOLOGY. 

57.  Physiology  claims  our  attention,  not  merely  as  an  orna- 
mental branch  of  speculative  knowledge,  but  as  a  science  of 
immediate  and  vast  practical  utility.  Numerous  are  the  occa- 
sions on  which  a  scientific  knowledge  of  the  structure  of  our  own 
bodies,  and  of  the  operations  that  are  carried  on  within  us,  is 
highly  valuable  to  its  possessor ;  and  more  especially  if  combined 
with  the  more  enlarged  views  derived  from  the  study  of  compa- 
rative physiology.  It  may  be  useful  here  to  point  out  some  of 
the  most  important  appUcations  of  physiological  knowledge. 

58.  It  is  scarcely  necessary  to  dwell  on  the  utihty  of  know- 
ledge of  anatomy,  enlightened  by  physiology,  in  its  application  to 
the  art  of  medicine;  for  the  very  foundations  of  that  art  must  be 
laid  by  these  sciences.  It  is,  however,  proper  to  advert  to  the 
limited  advantage  which  would  accrue  from  such  application  if 
those  sciences  were  confined  to  the  human  structure  and  the 
human  functions,  instead  of  comprehending  within  its  range  the 
whole  of  the  animal  creation.  All  the  important  discoveries  of 
modern  times  with  regard  to  the  economy  of  the  human  body 
have  been  derived  from  observations  made  on  the  lower  animals. 
That  of  the  circulation  of  the  blood,  for  instance,  which  has  im- 
mortalized the  name  of  Harvey,  was  obtained  principally  from 
this  source.  John  Hunter,  one  of  the  greatest  benefactors  to  the 
healing  art  in  modern  times,  was  so  deeply  impressed  with  the 
necessity  of  an  extended  study  of  comparative  physiology,  that 
he  devoted  his  whole  life  to  its  cultivation,  with  an  ardour  and 
a  perseverance  that  have  been  rarely  equalled,  and  never  sur- 
passed; as  is  attested  by  the  unrivalled  museum  of  preparations 
in  every  department  of  comparative  anatomy,  which  he  formed 


APPLICATION    TO    ZOOLOGr.  35 

by  his  own  unaided  exertions,  and  which  will  ever  remain  an 
imperishable  monument  to  his  fame. 

59.  The  various  combinations  of  faculties,  which  are  met  with 
in  the  different  tribes  of  animals,  exhibit  in  a  most  striking  man- 
ner the  mutual  dependence  and  relations  of  the  animal  and  vital 
functions.  As  if  with  the  express  intention  of  assisting  us  in  our 
physiological  researches  on  the  attributes  of  that  vitality  which 
eludes  our  experimental  investigations,  nature  offers  to  our  view, 
in  the  diversified  structures  of  each  successive  order  of  animals, 
a  series,  as  it  were,  of  varied  experiments ;  and  exhibits  the 
several  organs  under  every  degree  of  simphcity  and  complication 
of  structures,  and  every  possible  mode  of  combination.  The 
application  of  all  this  knowledge  comes  home  to  our  own  bosoms ; 
for  the  human  race  is  then  viewed  as  composing  a  member  of 
the  great  family  of  nature:  and  we  ourselves,  as  well  as  all  the 
individuals  of  that  race,  are  placed  under  the  governance  of  those 
general  laws  which  regulate  all  animated  beings.  Our  deepest 
interests,  our  future  comforts  and  enjoyments,  our  powers  of 
action,  our  intellectual  existence,  our  capacities  of  feeling  and  of 
reasoning,  all  that  renders  life  desirable,  nay,  that  very  life  itself, 
are  wholly  dependent  on  the  operation  of  those  laws,  and  on  the . 
minutest  results  produced  by  their  varied  combinations.  In  a 
word,  we  ourselves  are  animals,  and  nothing  that  relates  ever  so 
remotely  to  animal  life  can  be  to  us  a  matter  of  indifference. 

60.  Although  researches  into  comparative  physiology  neces- 
sarily imply  a  knowledge  of  the  forms  and  history  of  the  different 
races  of  animals,  it  tends  to  reffect,  in  its  turn,  the  most  important 
light  on  the  science  of  zoology;  and  more  especially  on  that  de- 
partment which  relates  to  the  classification  of  animals.  All 
scientific  knowledge  must  be  founded  on  correct  classification; 
but  in  zoology  a  methodical  arrangement  is  indispensable ;  for 
scarcely  any  progress  could  be  made  without  it.  The  number 
of  animals  in  the  habitable  globe  is  immense,  while  our  faculties 
and  means  of  observation  are  extremely  limited.  Of  insects 
alone,  the  number  of  distinct  species,  which  have  been  already 
determined,  considerably  exceeds  one  hundred  thousand.  Of  the 
other  classes  of  animals,  though  less  numerous,  the  catalogue  of 
known  species  is  af  least  half  as  great.  Each  of  these  races  of 
beings  has  its  distinct  and  characteristic  form,  its  peculiar  orga- 
nization, habits,  and  faculties.  It  is  obvious  that  if,  at  the  outset 
of  our  inquiries,  we  were  to  attempt  describing,  or  even  taking 
an  inventory  of  all  the  living  objects  that  presented  themselves 
to  our  notice  without  regard  to  any  principle  of  order,  our  atten- 
tion would  soon  be  distracted,  and  our  memory  overwhelmed  by 
the  confused  accumulation  of  details  ;  and  it  would  not  be  possi- 
ble to  deduce  from  them  any  useful  result.  Classification  affords 
the  only  clue,  which  can  extricate  us  from  this  intellectual  laby- 


36  PHYSIOLOGY. 

rinth,  which  can  resolve  this  state  of  chaos,  and  reduce  this 
crude  and  indigested  mass  of  materials  into  the  form  of  regular 
science.  It  is  only  by  a  methodical  arrangement  of  objects  that 
we  can  arrive  at  the  perception  of  the  more  extended  relations 
which  subsist  among  them,  or  establish  general  propositions,  em- 
bracing a  multitude  of  subordinate  facts,  and  capable  of  an  inde- 
finite number  of  useful  applications. 

61.  In  framing  a  system  of  classification  of  the  animal  king- 
dom, there  are  two  objects  which  we  have  in  view ;  first,  that  of 
being  able  readily  to  ascertain  the  name  of  any  animal  which 
may  present  itself  to  our  notice,  and  of  recognising  its  identity 
with  a  species  already  known  and  described ;  or,  secondly,  that 
of  becoming  acquainted  with  the  general  nature  and  character 
of  the  animal  in  question ;  with  the  affinities  which  it  has  with 
others  of  the  same  class,  and  with  the  rank  which  it  holds  in  the 
scale  of  animation.  The  first  of  these  objects  is  attained  by  what 
are  called  artificial  methods  of  classification ;  the  second  by 
what  are  called  natural  methods.  Much  error  and  confusion 
have  prevailed  in  the  reasonings  of  naturalists  from  their  ne- 
glecting to  discriminate  the  respective  objects  of  these  two 
kinds  of  methods,  which  nevertheless  are  perfectly  distinct  from 
each  other. 

62.  In  endeavouring  to  accomplish  the  first  of  these  objects, 
we  take,  as  it  were,  an  inventory  of  nature,  we  record  all  her 
productions,  and  follow  her  in  all  her  variations  ;  we  collect  the 
fullest  and  most  faithful  description  of  every  known  species,  and 
assign  to  each  a  particular  name. 

The  end  we  have  in  view  being  simply  to  devise  a  ready  me- 
thod of  identifying  animals,  we  follow  a  process  of  this  kind. 
We  first  unite  those  species  which  are  most  nearly  allied  to  each 
other  into  one  genus.  We  observe,  for  example,  several  species 
which  have  much  resemblance  to  the  stag ;  such  as  the  rein- 
deer, the  elk,  the  roebuck,  the  fallow-deer,'the  axis,  the  muntjac, 
and  several  others :  we  assemble  all  these  into  one  genus,  which 
we  call  the  deer  kind.  By  a  similar  process  we  form  another 
genus  of  animals  resembling  the  bull ;  such  as  the  buffalo,  &c. 
The  genus  antelope  will,  in  like  manner,  comprehend  the  gazelle, 
the  chamois,  the  nylghau,  the  oryx,  the  saiga,  the  gnu,  and  a 
multitude  of  others.  In  the  same  way,  the  camelopard,  the 
goat,  sheep,  camel,  and  musk,  may  be  regarded  as  so  many 
generic  terms,  each  including  a  number  of  different  animals, 
distinct  in  race,  but  similar  in  appearance.  Having  thus  consti- 
tuted the  genera,  we  may  apply  to  them  the  same  principle  of 
generalization  that  we  did  to  the  species ;  uniting  them,  accord- 
ing to  their  simiUtudes,  into  more  comprehensive  assemblages. 
Thus,  the  genera  above  mentioned,  having  many  features  of  re- ' 


APPLICATION   TO    ZOOLOGY.  37 

semblance,  are  considered  as  composing  a  tribe   or  order,  to 
which  Linna3us  has  given  the  name />ecora. 

63.  We  may  continue  this  process  till  we  have  gone  through 
the  whole  animal  kingdom;  but  it  will  then  be  necessary  to 
adopt  in  some  respects  a  contrary  method ;  and  instead  of 
ascending  as  we  have  done  from  particulars  to  generals,  to  de- 
scend from  generals  to  particulars.  Reo;ardin2[  the  animal  kincr- 
dom  as  one  entire  suoject,  we  must  partition  it  into  provinces, 
and  again  subdivide  these  into  smaller  portions.  All  these  divi- 
sions and  subdivisions  must  be  founded  upon  distinct  variations 
of  external  organs,  and  must  be  characterised  by  concise  defini- 
tions, enumerating  the  leading  circumstances  common  to  all  the 
animals  they  comprehend,  and  by  which  they  may  be  contrasted 
with  those  included  in  the  collateral  divisions.  The  great  pri- 
mary divisions  of  the  animal  kingdom  are  the  classes;  the 
subdivisions  of  these  form  the  orders;  these  comprehend  the 
genera,  which  again  include  the  separate  races  t)r  species ; 
while  the  ultimate  ramifications  of  the  system,  expressive  merely 
of  diversities  arising  in  the  same  race,  constitute  what  are  called 
varieties.  By  thus  confining  our  attention  to  a  small  number  of 
essential  characters,  we  are  enabled  to  ascertain,  by  a  sort  of 
analytical  process,  the  name  of  any  animal  that  we  may  wish  to 
examine  or  identify.  We  have  converted  our  rude  inventory 
into  a  convenient  dictionary  of  nature,  where  every  object  may 
be  found  at  its  appropriate  place.  The  characters  of  the  classes 
resemble  in  their  office  the  initial  letter  of  a  word ;  the  charac- 
ters of  the  subsequent  divisions  that  of  the  succeeding  letters, 
conducting  us  with  certainty  and  precision  to  the  place  we  seek. 
The  full  development  of  this  method,  and  of  the  logic  which 
should  regulate  it,  and  its  successful  application  to  natural  his- 
tory, we  owe  to  the  genius  and  industry  of  Linnasus,  to  whom 
the  science  will  ever  have  to  record  a  lasting  obligation. 

64.  But  however  perfectly  we  may  have  accomplished  the 
purpose  we  had  in  view  in  these  artificial  arrangements,  it  is 
impossible  not  to  perceive  that  we  have  obtained  them  by  the 
sacrifice  of  that  order  which  nature  herself  points  out.  A  strict 
adherence  to  any  arbitrarily  assumed  principle  of  classification, 
is,  in  truth,  incompatible  with  the  preservation  of  the  natural 
affinities  of  animals.  Thus,  in  the  system  of  Linn;cus,  the  order 
primates,  among  the  mammalia,  presents  the  incongruous  asso- 
ciation of  man  with  monkeys,  lemurs,  and  bats.  In  the  order 
bellucs,  the  horse  is  placed  by  the  side  of  the  hog.  The  ferce 
offer  us  the  unnatural  association  of  the  seal,  the  dog,  the  bear, 
the  opossum,  the  hedgehog,  and  the  mole,  merely  because  these 
animals,  in  most  respects  totally  dissimilar,  happen  to  agree  in 
having  the  incisor  teeth  of  a  conical  shape.  The  continual 
violation  of  natural  analogies,  which  is  yet  necessarily  incident 

4 


88  PHYSIOLOGY. 

to  all  artificial  systems,  has  exposed  them  to  much  censure  and 
ridicule,  from  those  who  forget  that  the  purpose  for  which  they 
are  framed,  is  that  of  convenient  reference,  and  that  it  is  essential 
to  arrangements  adapted  to  that  end,  that  they  should  be  arbi- 
trary. As  well  might  it  be  made  the  subject  of  complaint,  that, 
in  a  dictionary,  w^ords  having  very  different  m,eanings,  are  found 
placed  in  juxtaposition. 

65.  Cuvier  has  justly  remarked  that  a  perfect  natural  method 
should  be  the  expression  of  the  science  itself,  that  is,  of  its  most 
general  propositions.  By  assembling  animals  in  groups,  accord- 
ing to  their  general  resemblances  in  the  more  important  circum- 
stances of  their  organization  and  functions,  we  are  enabled  to 
connect  them  under  one  description,  and  afterwards  apply  to  each 
individual  species  ail  the  particulars  comprised  in  this  description, 
and  thus  we  obtain  more  or  less  comprehensive  statements,  or, 
as  it  were,  zoological  laws,  enabling  us  both  to  acquire  and  to 
retain  the  facts  wuth  greater  facility,  and  to  apply  them  with 
readiness  in  every  case  ;  in  a  word,  it  gives  us  the  entire  com- 
mand of  that  knowledge,  by  imparting  to  it  the  form  of  science. 
The  tribe  oi pecora,  formerly  mentioned,  may  be  taken  as  an  ex- 
cellent example  of  a  natural  family  of  animals;  for  they  consist  of 
species  which  bear  a  striking  resemblance  with  another  in  form, 
organization,  and  manners.  If  we  meet  with  a  new  animal  hav- 
ing one  or  two  of  the  leading  characters  of  this  tribe,  we  deduce  at 
once  all  the  most  important  features  of  its  history.  We  know,  for 
instance,  from  its  possessing  a  double  hoof,  that  it  belongs  to 
this  tribe,  and  consequently  that  it  feeds  on  herbage,  that  it  has 
four  stomachs,  and  that  it  ruminates  its  food ;  that  it  belongs  to 
a  species  disposed  to  assemble  in  flocks  or  herds,  and  that  it  has 
a  disposition  to  be  domesticated.  We  may  pronounce  that  its 
upper  jaw  has  no  incisor  teeth,  and  so  forth. 

66.  It  is  evident  that  from  the  discovery  of  these  analogies,  on 
which  the  arrangement  into  nat-ural  families  is  founded,  we  must 
resort  to  the  aid  of  comparative  physiology.  It  is  this  science 
alone  that  can  teach  us  to  discriminate  the  circumstances  which 
are  of  real  importance  in  the  animal  economy,  and  on  which 
their  very  nature  and  character  depend.  The  immense  progress 
which  has  been  made  in  this  branch  of  knowledge,  since  the 
lime  of  Linnaeus,  has  enabled  us  to  determine  with  much  greater 
precision  the  relative  affinities  of  animals,  and  the  rank  which 
each  tribe  is  entitled  to  hold  in  the  natural  system  of  classifica- 
tion. 

67.  Attempts  have  often  been  made  to  combine  these  two 
methods  into  one,  by  a  sort  of  mutual  compromise  between  them  ; 
that  is,  by  an  arrangement  partly  natural,  and  partly  artificial,  to 
obtain  the  principal  advantages  of  both.  The  most  perfect  speci- 
men of  this  union  of  the  two  methods  is  that  of  Dumeril,  which 


APPLICATION    TO    ZOOLOGY.  '  "39 

he  has  published  under  the  title  of  Zoologie  Analyiique.  The 
characters  on  which  his  divisions  are  founded  are  distributed 
in  a  strictly  analytical  order,  and  they  conduct  us  to  classes 
much  more  natural  than  those  of  Linnajus.  Thus,  he  divides  the 
Linnffian  class  of  insects  into  two,  namely,  Crustacea,  and  insects 
properly  so  called.  The  very  miscellaneous  class  of  vermes,  in 
which  animals  very  dissimilar  in  their  nature  had  been  thrown 
together,  as  it  were  in  a  lumber  closet,  compose  in  this  system 
the  more  natural  assemblages  of  moUusca,  vermes,  and  zoophytes. 
Dumeril  has  pursued  this  plan  throughout  the  whole  of  the  ani- 
mal kingdom,  reducing  all  the  characters  which  lead  to  the  deter- 
mination of  classes,  orders,  families,  and  genera,  to  the  form  of 
synoptic  tables. 

68.  The  arrangement  which  makes  the  nearest  approach  to  a 
natural  distribution  is  that  adopted  by  Cuvier  in  his  celebrated 
work,  entitled  Le  RSgne  Animal  Distribid  cTaprls  son  Organi- 
zation ;  as  it  is  founded  chiefly  on  the  structure  of  the  organs  most 
essential  to  life,  and  having  most  influence  in  determining  the 
intelligence,  sensibilities,  activity,  habits,  and  manners  of  animals. 
Physiology  is,  in  fact,  the  basis  of  Cuvier's  classification,  for  it 
proceeds  on  the  following  principles. 

69.  The  powers  of  sensation  and  of  voluntary  motion  being 
the  chief  attributes  of  animal  life,  it  follows  that  the  organs  of 
primary  importance  in  the  economy  are  those  which  are  imme- 
diately subservient  to  the  performance  of  these  functions.  They 
are,  as  we  have  seen,  the  organs  composing  the  nervous  system ; 
and  the  general  form  and  distribution  of  the  nervous  system, 
therefore,  should  lay  the  foundation  of  the  primary  divisions  of 
the  animal  kingdom.  There  appear  to  be  four  general  types  or 
models  of  structure  of  these  organs  presented  in  the  animal  crea- 
tion. The  first  consists  of  a  brain,  or  large  mass  of  nervous 
substance,  from  which  a  cylindrical  process,  called  the  spinal 
marrow,  is  continued  ;  and  these  are  protected  respectively  by 
the  bones  of  the  skull,  and  by  a  series  of  bones,  called  vertehrcB, 
which  form  a  jointed  column  along  the  whole  length  of  the  back. 
Animals  formed  on  this  construction  are  called  vertehrated 
animals,  a  division  which  comprehends  all  the  higher  classes  of 
the  animal  kingdom,  namely,  mammalia,  birds,  reptiles,  a.nd  fishes. 

In  the  second  form  of  the  nervous  system,  there  is  properly 
but  one  central  mass  of  nervous  substance,  or  brain,  without  any 
spinal  marrow,  and  from  this  mass  filamients  of  nerves  proceed, 
in  various  directions,  to  be  distributed  to  all  the  other  parts. 
This  division  comprehends  all  the  molliisca,  including  both  the 
mollusca  and  testacea  of  LinnoBUs. 

The  third  form  is  that  of  a  longitudinal  series  of  masses  con- 
nected together  by  lateral  filaments,  and  sending  out,  as  from  so 
many  centres,  ramifications  of  nerves.     This  structure  is  the  dis- 


40 


PHYSIOLOGY. 


tinctive  mark  of  articulated  animals,  and  may  be  recognised  in 
insects,  and  worms  properly  so  called. 

The  fourth  and  last  division  of  Cuvier,  he  denominates 
radiated  animals,  in  which,  wherever  nerves  are  found,  they 
appear  as  a  number  of  equal  masses  disposed  in  a  circle,  and 
sending  out  fibres,  which  diverge  hke  rays  from  a  common 
centre.  Hence  the  whole  body  of  the  animal,  or  at  least  some  of 
its  principal  organs,  has  a  radiated  or  starlike  form.  This  is  the 
case  with  the  asterias,  medusce, polypi,  and  all  the  other  animals 
comprehended  under  the  name  of  zoophytes. 

As  frequent  reference  will  be  made,  in  this  treatise,  to  the 
zoological  classification  of  Cuvier,  we  shall  here  give  a  table  of 
the  principal  divisions  which  it  comprises,  together  with  examples 
of  animals  included  in  each  order. 


I.  VERTEBRATA. 

1.    MAMMALIA. 

1.  Bimana Man. 

2.  Quadrumana Monkey,  ape,  lemur. 

3.  Cheiroptera Bat,  colugo. 

4.  Insectivora Hedgehog,  shrew,  mole. 

6.  Plantigrada Bear,  badger, ^glutton. 

6.  Pigitigrada ^"S-,  l^on,  cat,  martin,  weasel,  otter. 

7.  Amphibia Seal,  walrus. 

8.  Marsupialia Opossum',  kanguroo,  womlat. 

9.  Rodentia Beaver,  rat,  squirrel,  porcupine,  har". 

10.  Edentata Sloth,  armadillo,  anteater,  pangolin,  ornithorliynchus. 

11.  Pachydermata  ....  Elephant,  hog,  rhinoceros,  tapir,  horse.    • 

12.  Ruminantia Camel,  musk,  deer,  giraffe,  antelope,  u,oat,  sheep,  ox. 

13.  Cetacea Dolphin,  whale. 

2.   AVES. 

1.  Acclpitres Vulture,  eagle,  owl. 

2.  Passeres Thrush,  swallow,  lark,  crow,  sparrow,  urren, 

3.  Scansores Woodpecker,  cuckoo,  toucan,  parrot. 

4.  Gallinae Peacock,  pheasant,  grouse,  pigeon. 

5.  Graliae Plover,  stark,  snipe,  ibis,Jlatningo. 

6.  Pahnipedes Jluk,  grebe,  gull,  pelican,  swan,  duck. 

3.    REPTILIA.  » 

1.  Chelonia Tortoise,  turtle,  emys. 

2.  Sauria Crocodile,  lizard,  gecko,  chameleon. 

3.  Ophidia Serpents,  boa,  viper. 

4.  Batrachia Frog,  salamander,  newt,  proteus,  siren. 

4.   PISCES. 

1.  Acanthopterygii  ,  .  .  Perch,  mackerel,  sword-fish,  mullet. 

2.  Malacopterygii .  ,  .  .  Salmon, herring, pike, carp, silurus, cod, sole,rcmora, eel. 


APPLICATION    TO    ZOOLOGY.  41 

3.  Lophobranchii .  .  .  .  Pipe-fish,  pegasus . 

4.  Plectognathi Sun-fish,  trunk-fish. 

5.  Chondropterygii . .  .  Lamprey,  shark,  ray,  sturgeon. 

II.  MOLLUSCA. 

1.  Cephalopoda Cuttle-fish,  calamary,  nautilus. 

2.  Pteropoda Clio,  hyalsea. 

3.  Gasteropoda Slug,  snail,  limpet,  whelk. 

4.  Acephala Oyster,  muscle,  ascidia. 

5.  Brachiopoda Lingula,  terebratula.  •  , 

6.  Cirrhopoda Barnacle. 

III.  ARTICULATA. 

I.    ANNELIDA. 

1.  Tubicola Serpula,  sabella,  amphitrite. 

2.  Dorsibranchia  ....  Nereis,  aphodrite,  lob-worm. 

3.  Abranchia Earth-worm,  leech,  nais,  hair-worm. 

2.  CRUSTACEA. 

1.  Malacostraca 

Decapoda Crab,  lobster,  prawn. 

Stomapoda Squill,  phyllosoma, 

Amphipoda Gammarus,  sand-hopper. 

Lsemodipoda' Cyamus. 

Isopoda Wood-louse. 

2.  Entomostraca Monoculus. 

3.  ARACHNIDA. 

1.  Pulmonalia Spider,  tarantula,  scorpion, 

2.  Trachealia Fhalangium,  mite. 

4.    INSECTA. 

1.  Aptera Centipede,  podura. 

2.  Coleoptera Beetle,  glow-worm. 

3.  Orthoptera Grasshopper,  locust. 

4.  Hemiptera Fire-fly,  aphis. 

5.  Neuroptera Dragon-fly,  ephemera. 

6.  Hymenoptera Bee,  wasp,  ant. 

7.  Lepidoptera Butterfly,  moth. 

8.  Rhipiptera Xenos,  stylops. 

9.  Diptera Gnat,  house-fly. 

IV.  ZOOPHYTA. 

1.  Echinodermata  ....  Star-fish,  urchin. 

2.  Entozoa Fluke,  hydatid,  tape-worm. 

3.  Acalephse Actinia,  medusa. 

4.  Polypi Hydra,  coral,  madrepore,  pennatula. 

6.  Infusoria Brachionus,  vibrio,  proteus,  monas. 

4* 


42  PHYSIOLOGY. 

It  has  long  been  a  favourite  notion  with  speculative  naturalists, 
that  organized  beings  might  be  arranged  in  a  continued  series, 
every  part  of  which,  like  the  links  of  a  chain,  should  be  con- 
nected with  that  which  preceded  and  that  which  followed  it. 
Linneeus  was  even  impressed  with  the  idea  that  nature,  in  the 
formation  of  animals,  had  never  passed  abruptly  from  one  kind 
of  structure  to  another.  But  the  idea  of  a  chain,  or  continuous 
gradation  of  being,  was  cherished  with  enthusiastic  ardour  by 
Bonnet,  who,  assuming  man  as  the  standard  of  excellence, 
attempted  to  trace  a  regular  series,  descending  from  him  to  the 
unorganized  materials  of  the  mineral  world.  Many  other  writers 
have  adopted  this  speculation;  but  none  have  carried  it  to  a 
more  extravagant  length  than  Lamarck,  who  blends  it  with  the 
wildest  and  most  absurd  hypothesis  that  was  ever'  devised,  to 
account  for  the  diversities  of  animal  structures.  He  conceives 
that  there  was  originally  no  distinction  of  species,  but  that  each 
has,  in  the  course  of  ages,  been  derived  from  some  other  less 
perfect  than  itself,  by  a  spontaneous  improvement  in  the  race. 
He  believes  that  the  animalcula  of  infusions  gave  birth,  by  suc- 
cessive transformations,  to  all  other  animals ;  aquatic  animals 
acquiring  feet  and  legs,  fitting  them  for  walking  on  the  ground, 
and,  after  a  time,  being  converted  into  wings,  merely  from  the 
long  continued  operation  of  a  desire  to  walk  or  to  fly. 

70.  In  support  of  the  theory  of  continuous  gradation  many 
anomalous  animals  are  produced  as  instances  of  links  of  con- 
nexion between  different  classes  of  animals.  The  bat  has  been 
regarded  as  one  of  these  intermediate  links  between  mammalia 
and  birds.  The  cetaceous  tribe,  including  the  wliale,  cachalot, 
dolphin,  and  narwhal,  though  properly  belonging  to  the  class 
mammalia,  make  an  apparently  near  approach  to  the  tribe  of 
fishes.  The  ornithorhyncus  is  allied  both  to  quadrupeds  and 
to  birds.  Many  similar  examples  might  be  produced  among 
the  inferior  classes  of  the  animal  kingdom.  A  little  attention, 
however,  will  soon  enable  us  to  perceive  that  they  occupy  but 
small  portions  of  the  wide  spaces  intervening  between  different 
orders  of  animals.  Even  in  the  best  arranged  systems,  such  as 
that  of  Cuvier,  we  discover  innumerable  chasms  wholly  unoccu- 
pied, between  adjacent  orders ;  and  in  many  instances  animals, 
which  are  scarcely  in  any  respect  allied  to  each  other,  are  placed 
in  immediate  sequence.  This  defect,  as  I  have  already  observed, 
is  unavoidable,  because  it  is  inherent  in  the  very  nature  of  the 
subject.  Instead  of  a  single  continuous  line,  nature  presents  us 
with  a  multitude  of  partial  series,  with  innumerable  ramifications, 
and  occasionally  a  few  insulated  circles.  If  metaphor  must  be 
employed,  it  would  be  better  to  say,  that  instead  of  being  a  chain, 
the  natural  distribution  of  animals  ofi^ers  the  idea  of  a  complicated 
net-work,  where  several  parallel  series  present  themselves,  and 


APPLICATION    TO    GEOLOGY.  43 

are  occasionally  joined  by  transverse  or  oblique  lines  of  connexion. 
The  great  divisions  of  Cuvier  represent  these  principal  parallel 
scries.  The  last,  however,  or  that  of  the  radiata,  appears  to  be 
the  least  perfect  of  these  series,  and  might  with  advantage  be 
farther  divided. 

On  the  subject  of  natural  classification  Mr.  Macleay*  has  ad- 
vanced a  hypothesis,  which  he  supports  with  some  ingenuity, 
namely,  that  the  real  types  or  niodels  of  structure  may  be  repre- 
sented by  a  circular  or  recurring  arrangement ;  and  he  gives  a 
number  of  instances  in  which  this  principle  appears  very  happily 
to  apply.  But  speculation  on  these  subjects  can  lead  to  satisfac- 
tory conclusions  only  on  the  supposition  that  an  extensive  com- 
parison of  organs  has  been  instituted  throughout  the  whole  of  the 
animal  kingdom. 

71.  A  scientific  knowledge  of  the  organization  and   functions 
of  animals  is  valuable,  not  only  in  its  application  to  zoology,  but 
also  in  reference  to  many  other  sciences,  such  as  geology,  wath 
which  it  might  at  first  view  appear  to  have  but  little  connexion. 
By  attending  to  the  arrangement  of  mineral  bodies  as  they  occur 
in  nature,  we  have  sufficient  proofs  that  the  earth  has  undergone 
frequent  and  considerable  changes  prior  to  the  existence  of  any 
living  beings.     But  we  find,  besides,  a  great  number  of  strata, 
which  contain  unequivocal  remains  of  vegetable  and   animal 
bodies.     A  large  proportion  of  these  are  shells,  exuviae  of  zoo- 
phytes, and  other  marine  animals.    We  also  find,  in  other  strata, 
a  multitude  of  fossil  bones,  and  teeth  of  various  quadrupeds  and 
reptiles  ;  and  occasionally,  but  more  rarely,  of  birds  and  fishes. 
Whole  mountains  and  extensive  districts  appear  to  be  composed 
entirely  of  these  animal  remains.    It  is  by  the  aid  of  comparative 
anatomy  and  physiology  alone  that  we  are  enabled  to  compare 
these  relics  of  antiquky  with  similar  facts  of  hving  or  recent 
animals,  to  discover  their  difTerences  or  identity,  and  to  deduce 
certain  conclusions  with  regard  to  the  nature,  habits,  and  charac- 
ters of  the  animals  to  which  they  had  belonged;  and  by  studying 
their  relation  with  the  strata  in  which  they  are  found,  to  draw 
inferences  with  regard  to  the  changes  which  must  have  taken 
place  in  those  parts  of  the  earth,  inferences  which  are  of  the 
highest  importance  towards  estabhshing  a  correct  theory  of  those 
changes.  '  The  difficulties   attending  researches  of  this  nature 
were  of  course  exceedingly  great ;   but  they  have  been  at  length 
surmounted    by   the  persevering  zeal   and   industry  of  modern 
naturalists.     In  these  arduous  investigations  Cuvier  stands  pre- 
eminent; and  his  labours  have  been  rewatded  with  a  number  of 
highly  interesting  results.     The  great  principle  which  he  has  as- 
sumed as  the  foundation  of  his  researches,  is  that  every  organized' 

*  Macleay,  Horx  Entomohgicse,  or  Essays  on  Annulose  Animals,  1821. 


44  PHYSIOLOGY. 

individual  constitutes  a  system  of  itself,  of  which  all  the  parts  are 
connected  to  each  other  by  certain  definite  relations.  In  passing 
from  each  of  these  structures  to  that  of  other  animals  in  the 
natural  series,  we  find  that  all  the  changes  of  form  which  take 
place  in  any  one  organ  are  accompanied  by  corresponding  altera- 
tions in  the  form  of  every  other  organ ;  so  that  by  the  careful 
application  of  certain  rules,  deduced  from  this  observed  recipro- 
cal dependence  of  its  functions,  we  are  enabled  to  ascertain  with 
considerable  certainty  the  forms  and  habits  of  animals,  of  which 
only  small  fragments  have  been  preserved.  We  have  already 
given  an  instance  of  this  mode  of  reasoning  as  applied  to  rumi- 
nant animals.  By  following  this  guide  Cuvier  ascertained  and 
classed  the  fossil  remains  of  nearly  100  different  quadrupeds  in 
the  viviparous  and  oviparous  classes.  Of  these  above  seventy 
were  distinct  species,  hitherto  unknown  to  naturalists. 

It  appears  from  these  researches  that  the  earth  has  sustained 
more  numerous  convulsions  than  had  before  been  suspected,  and 
that  these  must  have  been  separated  by  considerable  intervals  of 
time;  that  the  ocean  has  deposited  various  strata  in  regular  suc- 
cession ;  that  the  species  of  animals  whose  remains  are  found  in 
these  strata  change  with  every  variation  in  the  nature  of  the 
deposit,  and  become  more  and  more  analogous  to  the  living 
animals  of  the  present  day,  in  proportion  as  the  deposits  have 
been  of  more  recent  date.  It  appears  from  an  examination  of 
these  fossil  remains,  that  the  sea  must  have  retired  at  intervals 
from  the  districts  it  had  formerly  covered,  and  left  dry  land, 
affording  habitation  for  large  quadrupeds ;  and  that  after  a  certain 
unknown  space  of  time,  the  sea  has  suddenly  returned  to  the  same 
spot,  has  destroyed  all  the  terrestrial  animals,  and  has  formed 
subsequent  deposits  of  shells  and  other  marine  productions. 

These  sudden  irruptions  and  recessions  of  tfie  ocean,  which 
have  occurred  several  times  in  the  same  district,  must  have  been 
attended  with  extensive  destruction  of  animal  life.  Whole  races 
have  perished  irretrievably,  and  are  known  to  us  only  by  the 
durable  memorials  they  have  left  behind  of  their  own  existence, 
and  of  the  several  epochs  of  antediluvian  chronology. 

72.  The  study  of  the  fossil  remains  of  animals  has  also  extend- 
ed our  views  of  the  animal  kingdom ;  it  has  in  many  instances 
supplied  chasms  which  had  occurred  in  the  natural  series,  and 
has  enlarged  our  ideas  of  the  extent  of  creative  power.  Another 
important  conclusion  which  has  resulted  is,  that  the  human  race 
has  been  the  last  created  ;  for  nowhere  do  we  find  any  vestiges 
of  human  bones.  These  researches  tend  also  to  throw  fight 
on  the  history  of  mankind,  and  to  refute  the  pretensions  to 
high  antiquity  which  have  been  arrogated  by  certain  nations, 
and  particularly  the  Chinese,  &c.  which  Voltaire  and  other  mo- 
dern philosophers  had  so  zealously  defended.     All  that  science 


APPLICATION    TO    NATURAL    THEOLOGY.  45 

has  brought  to  h'ght,  indeed,  is  in  conformity  with  the  testimony 
of  the  sacred  writings,  when  rationally  interpreted,  and  may 
even  be  adduced  as^'illustration  of  their  truth.  Geology  and 
comparative  physiology  concur  with  these  writings  in  teaching 
us  that  man  was  the  last  act  of  creative  power  ;  that  a  great 
catastrophe  took  place  on  the  surface  of  the  globe  a  few  thousand 
years  ago,  during  which  the  sea  covered  for  a  time  every  part 
of  the  land;  and  that  the  subsequent  diffusion  of  the  population 
of  the  earth  is  of  comparatively  recent  date.  It  is  pleasing  to 
see  conclusions,  derived  from  such  different  sources,  converging 
to  the  same  points,  and  affording  each  other  that  reciprocal 
confirmation  which  is  the  invariable  concomitant  and  surest  test 
of  truth. 

73.  The  enlarged  views  to  which  we  are  conducted  by  the 
study  of  comparative  physiology  afford  us  a  glimpse  of  some  of 
the  plans  or  models  of  structure  which  appear  to  have  been 
followed  in  the  formation  of  the  animal  world.  The  analogies  of 
form  discernible  in  corresponding  organs,  throughout  a  very  ex- 
tensive series  of  tribes,  have  been  lately  traced  and  developed 
with  extraordinary  care  by  the  modern  naturalists  of  the  French 
and  German  schools,  and  especially  by  Cuvier,  Blainville,  Sa- 
vigny,  Geoffroi  St.  Hilaire,  Oken,  Carus,  and  Milne  Edwards. 
The  conclusions  they  have  drawn  from  their  labours,  though 
sometimes  overstrained,  are  always  ingenious,  and  in  general 
satisfactory;  and  they  strongly  tend  to  prove,  that  several  dis- 
tinct types,  or  standards  of  figure,  have  been  adhered  to  in  all 
the  multiplicity  of  forms  with  which  it  has  pleased  the  Author  of 
nature  to  diversify  the  animal  creation.* 

74.  These  inquiries,  however,  suggest  still  higher  subjects  of 
contemplation.  They  illustrate  the  connexion  and  relationship 
of  every  part  with  the  rest  of  the  system.  They  prove  the  unity 
of  design  with  which  the  system  has  been  planned  and  executed. 
They  demonstrate  the  perfection  with  which  all  its  parts  are 
mutually  adjusted,  and  the  harmony  which  pervades  the  whole. 
The  evidences  of  express  design  and  contrivance  are  so  distinct 
and  palpable,  and  they  so  multiply  and  accumulate  upon  us  as 
we  advance,  that  they  may  almost  be  said  to  obtrude  themselves 
on  our  notice;  and  we  cannot  avoid  being  impressed  with  the 
notion  of  its  being  intended  that  we  should  observe  them.  Whilst 
the  purpose  to  be  answered  continues  the  same,  the  means  are 
varied  in  every  possible  manner,  as  if  designedly  to  display  to 
us  the  exhaustless  resources  of  inventive  power,  and  the  supreme 
intelligence  wdth  which  that  power  is  wielded.  Nor  is  it  possible 
to  overlook  the  general  object  to  which  every  thing  so  manifestly 

*  See  the  Bridgewater  Treause  on  Animal  and  Vegetable  Physiology, 
where  this  subject^is  enlarged  upon,  and  especially  the  chapter  on  "  Unity  of 
Design."     ii.  625.     [American  Edition,  ii.  437.] 


46 


PHYSIOLOGY. 


tends  in  the  system  of  animal  existence.  Every  element  in  every 
part  of  the  habitable  globe,  teems  with  life,  and  that  life  is  replete 
with  enjoyment.  Happiness  is  unquestionably  the  great  object  of 
animal  existence.  The  benevolence  which  pervades  the  whole 
system  of  creation,  is  no  less  conspicuous  than  the  power  and 
intelligence  from  which  it  emanated.  Revealed  religion  is  thus 
in  unison  with  the  theology  derived  from  the  contemplation  of 
nature,  and  the  lights  of  modern  science. 

75.  The  facts  derived  from  comparative  physiology  which 
more  especially  support  the  arguments  of  natural  theology  have 
been  collected  by  authors  who  have  written  professedly  on  the 
subject.  Derham's  work,  entitled  Physico-Theology,  has  been 
deservedly  held  in  estimation ;  but  since  the  time  it  was  published, 
which  is  now  above  a  century,  the  sciences  have  been  prodigi- 
ously, extended.  Dr.  Paley,  in  his  Natural  Theology,  has  pro- 
duced a  great  multitude  of  facts  and  observations  in  support  of 
the  same  arguments,  has  applied  them  with  singular  felicity,  and 
impressed  them  with  the  most  fascinating  perspicuity  and  elo- 
quence. But  his  object  being  purely  theological,  he  has  not 
professed  to  adhere  to  any  scientific  order  in  stating  them.  The 
design  of  the  Bridgewater  Treatise,  already  referred  to,  is  to 
supply  this  desideratum,  by  presenting  the  details  of  animal  and 
vegetable  physiology,  arranged  according  to  the  functions  to 
which  they  relate,  or  in  other  words,  in  reference  to  final  causes. 
As  theological  arguments,  the  value  of  these  facts  cannot  fail  to 
be  better  appreciated  when  they  are  studied  in  all  their  bearings, 
and  as  forming  a  part  of  the  science  to  which  they  belong.  It 
is  by  the  aid  of  genuine  science  alone,  that  we  can  avoid  the 
dangerous  error  of  building  arguments,  on  so  momentous  a  sub- 
ject, upon  equivocal  or  unstable  foundations,  and  of  injuring  a 
cause  already  established  upon  incontrovertible  grounds,  by 
weak  and  inconclusive  evidence. 

76.  It  has  been  too  hastily  inferred,  from  the  abuse  which  has 
too  often  been  made  of  philosophical  inquiries,  that  they  are  to 
be  avoided  as  dangerous,  and  even  pernicious ;  and  that  of  the 
fountain  of  philosophy,  as  of  the  Pierian  spring,  we  should  "drink 
deep,"  or  abstain  from  tasting.  Superficial  knowledge  has  often 
been  decried  as  mischievous,  and  extremely  liable  to  abuse. 
The  hackneyed  maxim  of  Pope,  that  "  a  little  knowledge  is  a 
dangerous  thing,"  has  furnished  a  ready  text  for  those  who  de- 
claim against  all  attempts  to  render  science  popular,  and  to 
include  it  as  a  branch  of  general  education.  Willing  proselytes 
to  this  doctrine  will  always  be  found  among  those  whom  indo- 
lence or  frivolity  render  averse  to  mental  exertion,  when  bestowed 
on  subjects  not  immediately  connected  with  the  common  concerns 
of  life,  as  well  as  among  those  who,  already  enjoying  some  of  the 
advantages  of  knowledge,  are  desirous  of  securing  to  themselves 


ARRANGEMENT    OF    FUNCTIONS.  47 

the  monopoly  of  those  advantages.  But  their  sophistry  is  soon 
detected  when  we  examine  inio  the  real  meaning  of  the  expres- 
sions they  employ.  What  is  commonly  denominated  superficial 
knowledge,  may  certainly  be  useless,  or  even  dangerous;  but  the 
mischief  or  danger  arises,  not  because  it  is  superficial,  but  be- 
cause it  is  incorrect.  It  is  error,  under  the  guise  of  knowledge 
that  alone  deserves  such  reprobation.  The  value  of  information 
is  to  be  estimated  much  more  by  its  accuracy,  than  by  its  extent. 
Although  it  may  be  true  that  there  is  no  royal  road  to  science, 
it  is  equally  true  that  many  are  the  roads  that  lead  astray;  and 
that  much  fruitless  labour  may  be  spared  by  having  that  one 
pointed  out  which  leads  directly  to  the  object  we  wish  to  attain. 
Though  the  distance  we  have  to  travel  cannot  be  abridged,  yet 
the  path  may  be  rendered  smoother,  and  the  velocity  of  our  pro- 
gress accelerated,  by  availing  ourselves  of  such  guidance  as  may 
be  afforded  by  concise  treatises,  which,  however  superficial  in 
appearance,  or  popular  in  their  garb,  are  yet,  as  far  as  they  go, 
perspicuous,  accurate,  and  comprehensive. 


CHAPTER  III. 


ARRANGEMENT  OF  FUNCTIONS. 


77.  The  general  review  we  have  taken,  in  our  introductory 
chapter,  of  the  objects  and  mutual  connexions  of  the  functions 
of  the  animal  economy,  will  furnish  us  with  the  principles  on 
which  the  methodical  arrangement  and  classifiation  of  those 
functions  should  be  established.  Various  attempts  have  been 
made  by  different  systematic  writers  on  physiology  towards  the 
accomplishment  of  that  object ;  but  they  have  generally  been 
deficient  in  that  logical  precision,  which  alone  can  ensure  entire 
comprehensiveness  of  every  branch  of  the  subject,  and  at  the 
same  time  convey  clear  perceptions  of  the  bearings  of  every  part 
to  one  another.  Some  physiologists  have  limited  their  views  to 
the  human  economy,  or  that  of  animals  which  most  nearly  resem- 
ble man ;  others  have  framed  their  systems  so  as  to  embrace  the 
whole  animal  kingdom,  and  even  all  beings  endowed  with  life. 
Some  have  been  wholly  governed  by  anatomical  considerations, 
regarding  mere  structure  as  the  basis  of  physiological  distinctions  ; 
others,  overlooking  the  unity  of  purpose  in  each  function,  and 
pursuing  their  subdivisions  to  an  excessive  degree  of  minuteness, 
have  overloaded  the  subject  by  needless  multiphcation  and  super- 


48  PHTSIOLOGr. 

fluity  of  detail.  Many  have  introduced  confusion  by  a  loose  and 
villous  nomenclature,  derived  from  partial  or  hypothetical  views; 
which  were  often  tinctured  with  mysticism,  and  which,  by  biass- 
ing  their  judgments,  have  betrayed  them  into  a  wide  field  of  de- 
lusion and  of  error. 

78.  Another  source  to  which  the  greater  part  of  the  mistakes, 
pervading  all  the  systems  of  physiological  arrangement  that  have 
been  hitherto  framed,  may  be  traced,  is  inattention  to  the  essen- 
tial distinction  which  exists  between  physical  and  final  causes. 
The  study  of  the  phenomena  of  life  differs  from  all  the  other 
branches  of  philosophical  inquiry,  by  its  involving  considerations 
relating  to  both  these  kinds  of  causes  ;  the  latter  of  which  introduces 
a  totally  new  principle  of  arrangement,  wholly  inapplicable  in 
those  sciences  which  concern  the  physical  properties  of  inert  and 
inorganic  matter.  The  rules  of  a  strictly  philosophical  induction, 
which  alone  can  guide  our  steps  in  the  pursuit  of  these  sciences, 
must  be  greatly  modified,  and  in  some  measure  superseded,  by 
those  derived  from  another  department  of,  human  knowledge, — 
namely,  psychology.  The  knowledge  of  those  general  facts, 
which,  when  once  estabhshed,  and  the  conditions  on  which  they 
depend  ascertained,  constitute  what  are  called  the  laws  of  nature, 
is  obtained  first,  by  comparing  together  phenomena,  and  uniting 
in  one  class  such  as  are  of  the  same  kind,  and  carefully  separa- 
ting them  from  others  which  are  essentially  different ;  and  next, 
by  endeavouring  to  remove  all  extraneous  influences,  so  as  to 
reduce  each  class  of  phenomena  to  its  simplest  conditions ;  an 
object  to  be  attained  by  experiments,  that  is,  by  varying  the  cir- 
cumstances under  which  they  occUr,  and  also  by  combining 
them  in  different  ways,  so  as  to  enable  us  to  verify  our  theories, 
by  comparing  their  results  with  the  actual  observation  of  nature. 
But  the  attempt  to  apply  the  same  process  of  induction  to 
the  physiology  of  organised  beings,  is  attended  with  peculiar  dif- 
ficulty; for  while  the  changes  v/hich  occur  in  their  organic  world 
exhibit  the  operation  of  forces  or  agents  characterized  by  their 
simplicity,  their  constancy,  and  their  uniformity,  the  phenomena 
presented  to  our  view  by  living  beings,  so  prodigiously  varied  in 
their  form,  so  extensively  spread  throughout  every  element,  every 
clime,  and  every  habitable  region  of  the  globe,  and  so  infinitely 
diversified  in  their  nature,  and  complicated  in  their  connexions, 
are  calculated  to  baffle  the  efforts  of  the  most  cautious  reasoner, 
and  elude  the  penetration  of  the  most  sagacious  inquirer  after 
truth.  The  resources  of  experimental  research  are  here  ex- 
tremely narrowed,  in  consequence  of  the  simultaneous  and  con- 
nected operation  of  a  great  number  of  powers,  which  prevent 
us  from  studying  the  influence  which  each  would  exert  when 
isolated  from  the  rest,  and  ascertaining  the  laws  which  are  pecu- 
liar respectively  to  each.     Hence  it  is,  that  we  have  hitherto 


ARRANGEMENT    OF    FUNCTIONS.  49 

made  but  very  imperfect  approaches  to  the  determination  of  those 
laws. 

79.  Some  compensation  is,  however,  afforded  us,  while  strug- 
gling with  the  obstacles  which  impede  our  progress  in  the  direct 
and  thorny  path  of  science,  by  the  abundant  resources  accessible 
to  us  in  the  psychological  considerations,  which  everywhere  arise 
in  this  vast  field  of  contemplation.  All  the  phenomena  of  organic 
beings  reveal  to  us  so  palpably  the  indications  oi  design,  that  we 
cannot  resist  the  impression  thus  created  in  our  minds;  nor  can 
we  avoid  recognising  the  connections,  which  are  so  established 
between  the  objects  and  the  changes  they  present,  as  being  those 
of  means  employed  for  the  accomplishment  of  certain  ends.  Thus, 
then,  the  relation  of  means  to  ends  becomes  a  leading  principle  of 
association  among  the  facts  of  physiology:  giving  a  new  aspect  to 
the  science  and  creating  an  interest  of  a  different  and  much  higher 
kind,  than  could  ever  be  inspired  by  the  study  of  mere  physical  rela- 
tions. So  deep  has  been  this  impression,  and  so  completely  has 
the  principle  of  final  causes  been  interwoven  with  the  pursuits  of 
physiologists,  that  the  study  of  the  functions  of  life,  that  is,  of 
the  purposes  to  which  the  actions  constituting  life  are  subservient, 
has  been  almost  universally  regarded  as  the  principal,  if  not  the 
sole  object  of  the  science.  It  has,  accordingly,  been  assumed  as 
the  basis  of  arrangement,  in  all  systematic  treatises  of  Physiology: 
and  likewise  in  framing  theories  for  explaining  the  phenomena 
of  life,  physiologists  have  generally  been  satisfied  with  pointing 
out  their  final,  rather  than  their  physical  causes. 

80.  This  natural  proneness  to  substitute  final  for  physical 
causes  has  been  a  frequent  source  of  delusion,  by  insensibly  lead- 
ing to  the  belief  that  we  have  reached  the  physical  law  which 
regulates  the  phenomena  we  are  viewing,  when  we  have,  in  fact, 
done  nothing  more  than  traced  their  relation  to  the  intelligent 
agency  by  which  they  have  been  each  adjusted  to  their  respective 
objects,  and  given  that  law  a  name  with  reference  to  that  agency; 
thus,  in  our  eagerness  to  grasp  at  hidden  knowledge,  mistaking 
the  shadow  for  the  substance, 

81.  Frequent  instances  of  this  confusion  of  ideas  occur  in  the 
writings  of  the  older  physiologists;  but  at  all  times  the  predominant 
tendency  has  been  to  refer  the  phenomena  to  their  final  causes  ; 
that  is,  to  the  purposes  which  they  answer  in  the  animal  economy. 
The  functions  were  arranged  by  the  ancients  into  three  classes, 
designated  by  the  titles  of  animal,  vital,  and  natural ;  the  first 
comprising  those  powers  of  sensation  and  of  voluntary  motion  ■ 
which  are  more  especially  characteristic  of  animal,  as  contra- 
distinguished from  vegetable  life ;  the  second,  those  powers,  the 
coniinued  exercise  of  which  are  immediately  necessary  for  the 
maintenance  of  life,  such  as  respiration  and  the  circulation  of 
the  blood ;  and  the  third,  those  which  are  directly  concerned  in 

5 


50  PHYSIOLOGY. 

the  continuance  of  its  vital  actions,  but  which  are  yet  indispensable 
in  preserving  the  organs  in  the  conditions  enabling  them  to  perform 
their  respective  ofKces,  by  supplying  the  materials  requisite  for 
their  nutrition,  and  for  counteracting  their  tendency  to  decom- 
position ;  in  this  class  were  included  digestion,  secretion,  and 
absorption.  To  these  were  added  by  many,  o.  fourth  class,  the 
generative,  comprehending  all  the  functions  which  have  for  their 
object  the  continuance  of  the  species  by  the  reproduction  of  in- 
dividuals similar  to  the  parent  animal.  The  principal  objection  to 
this  arbitrary  division  of  the  functions  is,  that  the  line  cannot  be 
drawn  with  sufficient  distinctness  between  what  are  called  the  vital 
and  the  natural  functions,  their  connexion  with  the  maintenance 
of  life  being  one  of  degree  only,  and  not  of  kind  ;  as  is  evident  from 
their  being  united  together  in  the  lowest  tribes  of  the  animal 
kingdom.  This  classification  appears  also  to  be  defective,  inas- 
much as  it  omits  all  notice  of  those  functions  which  have  immediate 
reference  to  the  mechanical  condition  of  the  frame  ;  conditions 
which  are  the  foundation  of  their  physical  capabilities  of  executing 
the  operations  assigned  them  in  their  respective  places  in  the 
general  system.  It  is  also  liable  to  the  imputation  of  employing 
terms  to  designate  the  classes  which  are  obviously  incorrect,  and 
bear  not  the  meaning  they  are  intended  to  convey.  In  one  sense, 
and  that  which  would  first  present  itself  to  the  mind,  the  term 
animal  functions  would  comprehend  all  the  others,  for  there  are 
none  in  which  powers  peculiar  to  animal  life  are  not  called  into 
play ;  and,  on  the  other  hand,  the  strictly  animal  functions  are 
equally  entitled  to  the  appellation  of  vital,  as  being  directly  es- 
sential to  the  support  of  life;  and  no  specific  meaning  can  attach 
to  the  term  natural,  as  applied  to  any  description  of  functions. 

82.  Vicq  D'Azyr  proposes  to  estabhsh  a  preliminary  division 
of  the  functions  into  two  great  classes  ;  the  first,  comprising  those 
concerned  in  the  preservation  of  the  individual;  and  the  second, 
those  concerned  in  the  preservation  of  the  species.  The  former 
class  he  divides  into  two  orders ;  the  first  having  for  their  object 
the  assimilation  of  food  into  the  substance  of  the  body,  and  de- 
signated as  the  interior  assimilative  and  nutritive  functions ;  and 
the  second,  establishing  the  relations  of  the  individual  to  sur- 
rounding objects,  and  denominated  the  exterior  or  relative  func- 
tions. 

The  first  of  these  orders  comprises  six  genera;  namely,  1st, 
digestion,  by  which  the  nutritive  particles  are  extracted  from 
the  food ;  2d,  absorption,  by  which  this  nutritive  matter  is  con- 
veyed into  the  blood  ;  3d,  circulation,  by  which  it  is  carried  to 
all  the  organs ;  4th,  respiration,  by  which  it  is  exposed  to  the 
influence  of  atmospheric  air;  5th,  secretion,  by  which  it  is  made 
to  undergo  various  modifications ;  6th,  nutrition,  by  which  it  is 
applied  to  the  organs  for  the  purposes  of  growth  and  nourish- 
ment. 


ARRANGEMENT    OF    FUNCTIONS.  51 

The  second  order  of  the  first  class  comprehends  three  genera; 
namely,  1st,  the  sensations,  which  give  to  the  individual  notice 
of  the  presence  of  surrounding  objects;  2d,  the  motions,  which 
bring  him  towards,  or  remove  him  from  them  ;  3d,  voice  and 
speech,  which  enable  him  to  communicate  with  his  fellows  with- 
out transporting  his  body  to  a  diflerent  place. 

The  second  class,  or  the  generative  functions,  likewise  com- 
prise two  orders;  the  first,  including  the  functions  of  conception 
diXid  generation,  recimnng  \he  concourse  of  both  sexes;  the  se- 
cond, \nc\\yA'mg  gestation,  parturition,  and  lactation,  performed 
exclusively  by  the  female.  To  these  were  subjoined  by  Vicq 
d'Azyr,  as  a  kind  of  supplement  to  his  system,  the  several  facts 
relating  to  the  progressive  changes  taking  place  during  the  ad- 
vance of  life  from  infancy  to  decrepitude,  through  the  ages  of 
growth,  of  maturity,  and  of  decay,  and  to  those  which  attend 
the  absolute  extinction  of  life,  and  the  subsequent  decomposition 
of  the  organs. 

The  arrangement  of  Vicq  d'Azyr  is  entitled  to  much  commen- 
dation, and  has  been  followed  in  all  its  essential  features  by 
Dumas,*  Richerand,-|-  and  other  systematic  authors  on  physiology, 
with  the  exception  of  Haller^J  who  adopted  a  classification  of 
functions  founded  altogether  on  the  anatomical  relations  of  the 
organs  by  which  they  are  performed. 

83.  Bichat,§  whose  original  genius  led  him  to  disregard  the 
opinions  of  his  predecessors,  and  to  strike  out  for  himself  new 
paths  of  inquiry,  aimed  at  giving  greater  simplicity  to  physiolo- 
gical classification,  by  pursuing  a  more  rigid  analysis,  and  in- 
fusing a  more  philosophical  spirit  into  tlie  methods  of  research. 
With  this  view  he  distributed  the  functions  into  two  classes, 
which  he  denominates  respectively  the  animal  and  the  organic ; 
the  former  coinciding  nearly  with  those  already  known  by  that 
title ;  and  the  latter  comprehending  both  the  vital  and  the  natural 
functions  of  preceding  writers.  Impressed,  however,  with  the 
necessity  of  drawing  distinction  among  the  powers  of  life,  he  has 
perplexed  his  system  by  intermixing  with  those  final  causes, 
which  he  takes  as  the  basis  of  his  divisions,  the  results  of  a 
philosophical  analysis  of  those  powers.  He  is  thus  led  to  make 
continual  eftbrts  to  establish  a  distinction  between  muscular  con- 
tractibility — which  is  one  of  the  simple  and  elementary  powers 
of  life — when  that  power  is  employed  in  subservience  to  the 
animal  functions,  and  when  it  is  subservient  to  the  functions  of 
organic  life ;  a  distinction  which  regards  only  the  final,  and  not 
the  physical  causes  of  the  phenomena.  Dumas  has  been  guilty 
of  a  still  more  palpable  error  in  deeming  it  necessary  to  add  to 

*  Principes  de  Physiologie.  X  Elemens  de  Physiologie. 

f  Primffi  Lineee  Physiologiae.  §  Anatomie  Generale., 


52  PHYSIOLOGY. 

his  catalogue  of  principles,  consisting  of  the  acknowledged 
powers  of  sensibility  and  contractility,  a  third  power,  which  he 
terms  "  the  force  of  vital  resistance ;"  thus  associating  a  final 
cause  in  the  same  rank  with  causes  that  are  strictly  physical. 

84.  To  the  animal  and  vital  functions  of  Bichat,  Cuvier  has 
added,  in  his  physiological  arrangement,  a  third  class,  the  gene- 
rative, which  cannot,  indeed,  be,  with  any  propriety,  included 
in  any  of  the  former.  He  still,  however,  falls  into  a  similar  mis- 
take as  that  of  Dumas,  which  we  have  just  now  pointed  out ;  for 
he  describes  sensibiUty  and  muscular  contractility  not  as  primary 
principles,  but  both  of  them  as  functions  of  the  nerves.  Adelon* 
distinguishes  the  following  eleven  actions  as  being  the  functions 
of  life ;  namely,  sensibility,  locomotion,  language,  digestion, 
absorption,  respiration,  circulation,  nutrition,  calorification, 
secretion,  and  generation.  Bourdonf  reduces  them  to  seven, 
which  are  as  follows:  caloricit^,  nutrivit^,  absorptiviti,  exkala- 
tivite,  durabilite,  reproductivite,  et  resistabilit^ ;  -thus  presenting 
a  strange  jumble  between  physical  principles  of  action,  and 
actions  referred  to  definite  purposes.  The  same  confusion  may 
be  remarked  in  the  classification  of  the  functions  by  Bec]ard,J  who 
has  arranged  them  into  six  classes,  viz.  nutrition  in  its  most 
extended  sense,  generation,  muscular  action,  sensation,  nervous 
action,  and  the  functions  of  the  intellect.  But  it  would  be  need- 
less to  multiply  examples  of  this  error,  since  it  will  be  found  to 
pervade  almost  every  physiological  system  that  has  yet  been 
framed,  not  excepting  even  that  adopted  by  Dr.  Bostock,  in  his 
valuable  Elementary  System  of  Physiology. 

85.  Dr.  Bostock  regards  contractility  and  sensibility  as  the 
two  primary  attributes  of  animal  life,  each  equally  characteristic 
of  it,  and  peculiar  to  it,  and  each  performed  by  its  appropriate 
organs.  "  The  functions,"  he  remarks,  "  depend  on  the  exercise 
of  these  powers,  and  although  probably,  in  all  cases,  they  are 
both  of  them  exercised,  yet  generally  one  of  them  seems  to  be 
the  principal  agent,  or  the  prime  cause  of  the  ensuing  operation ; 
we  may  consequently  divide  them  into  the  contractile  and  sen- 
sitive functions,  or  those  which  more  directly  belong  to  contrac- 
tility and  to  sensibility,  and  which,  of  course,  serve  respectively 
for  motion  and  sensation,  and  to  these  two  classes  must  be  added 

*  Physiologie  de  I'Homme.  [The  arrangement  of  Adelon  is  adopted  from 
Magendie,  and  has  been  embraced  by  Dr.  Dunglison.  The  functions  are 
divided  into  three  classes.  'Vhe  first  class,  X\\e  functions  of  relation,  or  animal 
functions,  includes  those  that  establish  our  connexion  with  the  bodies  surround- 
ing us  ; — the  sensations,  voluntary  motions,  and  expressions.  The  second  class 
— \he  functions  of  nutrition — comprises  digestioii,  absorption,  respiration,  circu- 
lation, nutrition,  calorification,  and  secretion  ,-  and  the  third  class,  the  functions 
of  reproduxtion, — generation. — Duno-lison's  Human  Physiology,  3d  edit.  i.  51. 
Philad.  1838.] 

f  Elemens  d'Anatomie.  X  Pnncipes  de  Physiologie  Medicale. 


ARRANGEMENT    OF    FUNCTIONS.  53 

a  third  class  of  the  intellectual  functions."  Anaong  the  contrac- 
tile functions,  the  essence  of  which  consists  in  motion,  Dr.  Bos- 
tock  considers  the  circulation  as  being  the  first  in  point  of 
importance,  and  the  one  which  may  be  regarded  as  the  most 
necessary  to  the  direct  support  of  life,  and  to  the  indirect  main- 
tenance of  all  the  rest.  Next  in  importance  is  respiration,  which 
modifies  the  blood  so  as  to  adapt  it  to  the  maintenance  of  life. 
After  these  two  functions,  by  the  former  of  which  the  blood  is 
carried  to  all  the  parts  of  the  body,  and  by  the  latter  of  which  it 
acquires  its  vital  properties,  Dr.  Bostock  places  those  of  calorifi- 
cation, secretion,  digestion,  including  assimilation  and  sanguifica- 
tion, and  absorption,  functions  which  contribute,  he  observes,  to 
the  continuance  of  the  motion  of  the  animal  machine,  and  which 
preserve  all  its  parts  in  their  proper  condition,  without,  however, 
being  essential  to  the  immediate  support  of  life.  In  this  class  he 
places  the  function  of  generation,  which,  although  one  of  the 
most  inexplicable  of  all  the  operations  that  are  performed  by  the 
animal  powers,  and  acting  in  a  specific  manner,  of  which  we 
have  no  other  example,  may  be  considered  as  essentially  consist- 
ing in  secretion. 

The  sensitive  functions  are  divided  by  Dr.  Bostock  into 
two  classes ;  first,  those  which  originate  in  the  action  of  the 
external  agents  on  the  nervous  system ;  and,  secondly,  those 
of  a  reverse  kind,  which  depend  on  the  reaction  of  the  nervous 
system  on  these  agents.  In  the  first  of  these  divisions  are 
included  what  are  called  the  external  senses,  the  sight,  hear- 
ing, taste,  smell,  and  touch ;  and  in  the  same  division  must 
be  placed  the  sensation  of  hunger,  that  of  -temperature,  and 
some  others,  which  have  not  been  correctly  discriminated  from 
general  feeling,  but  which  possess  specific  characters.  In  the 
second  class, — those  functions  which  depend  on  the  reaction  of 
the  nervous  system  on  external  bodies, — he  places  volition;  and  to 
the  same  class  he  also  relers  instinct,  association,  sympathy, 
habit,  and  some  other  faculties  of  a  similar  kind,  which  appear 
to  hold  an  intermediate  rank  between  the  corporeal  actions  and 
those  of  a  purely  intellectual  nature.  As  the  functions,  which 
compose  the  first  of  these  classes,  may  be  all  referred  to  a  species 
of  perception,  so  the  latter  may  be  considered  as  more  or  less 
analogous  to  volition ;  in  the  former,  the  effect  on  the  nervous 
system,  whatever  it  may  be,  is  propagated  from  the  extremities 
to  the  centre  ;  in  the  latter,  it  proceeds  in  the  opposite  direction, 
from  the  centre  to  the  extremities  of  the  body. 

The  intellectual  functions  compose,  in  this  arrangement,  the 
third  class.  These,  Dr.  Bostock  observes,  are  a  less  direct  object 
of  physiology  than  the  two  former,  yet  many  of  them  are  so 
closely  connected   with  the  physical  changes  of  the  body  as 

5* 


54  PHYSIOLOGY. 

to  require  being  included  in  a  complete  view  of  the  animal 
economy.  Among  those  intellectual  operations  which  possess  a 
decided  action  on  the  corporeal  frame,  he  places  the  passions  ; 
and  also  refers  to  this  class  that  compound  of  mental  and  physi- 
cal influence,  from  which  results  what  are  called  temperament 
and  character.  These  lead  to  the  consideration  of  functions  of 
a  more  purely  and  intellectual  kind,  which  as  they  recede  from 
the  corporeal,  and  advance  towards  the  mental  part  of  our  frame, 
are  less  within  the  province  of  the  physiologist,  and  belong  moie 
to  the  metaphysician  or  the  moralist. 

86.  Dr.  Alison*  has  adopted  a  principle  of  arrangement,  which, 
though  differing  in  some  of  its  applications,  is  essentially  the  same 
as  that  of  Dr.  Bostock,  as  it  is  derived  from  the  analysis  of  the 
phenomena  of  life  into  certain  powers;  or  if  these  phenomena  be 
considered  as  the  results  of  a  single  principle,  which  we  may 
denominate  vitality,  the  study  of  physiology  will  resolve  itself 
into  an  inquiry  into  the  conditions  under  which  the  various  phe- 
nomena of  life  take  place,  that  is,  into  the  laios  of  vitality.  These 
laws  are  ranked  by  Dr.  Alison  under  three  heads  :  1.  Those  of 
vital  contractions,  by  which  the  visible  movements  of  living 
animals  are  chiefly  effected :  '2.  Those  of  vital  affinities,  by 
which  the  chemical  changes  peculiar  to  living  animals  are  deter- 
mined, and  their  physical  structure  maintained:  3.  Those  of 
nervous  actions,  by  which  the  physical  changes  in  living  animals 
are  placed  in  connection  with  mental  phenom.ena,  and  subjected 
to  the  control  of  mental  acts.  The  first  and  third  of  these  divi- 
sions correspond  to  those  of  Dr.  Bostock,  which  he  has  denomi- 
nated the  contractile  and  the  sensitive  functioils.  The  second 
division  of  Dr.  Alison  is  founded  on  the  principle  pointed  out  by 
the  author  in  a  treatise  on  Physiology  which  appeared  many 
years  ago  in  the  last  Supplement  to  the  Encyclopgedia  Britannicaj, 
and  to  which  he  gave  the  designation  of  the  organic  affinities. 

Dr.  Alison  considers  that  the  movement  of  the  fluids,  in  all  the 
higher  classes  of  animals,  is  in  a  great  measure  dependent  on 
vital  contractions  in  certain  of  their  solids,  and  may  accordingly 
be  regarded  as  the  first  and  most  important  consequence  of  the 
exercise  of  the  vital  power.  This  subject  he  divides  into  two 
parts;  first,  the  movement  of  the  mass  of  blood  in  the  heart,  ar- 
teries, and  veins,  or  the  function  of  circulation ;  and,  secondly, 
the  continual  evolution  of  matters  from,  and  absorption  of  matters 
into,  the  mass  of  blood  ;  or  the  functions  of  nutrition,  exhalation, 
secretion,  and  absorption,  to  which  the  circulation  is  subservient, 
and  on  which  all  the  other  functions  are  dependent.  The  study 
of  these  nutritive  functions  naturally  introduce  the  consideration 
of  the  properties  of  the  dilferent  textures   and   secretions  which 

*  Outlines  of  Physiology  and  Pathology,  Edinburgh,  1833. 


ARRANGEMENT    OF    FUNCTIONS.  55 

are  formed  from  the  blood,  and  which  are  the  materials  combined 
in  the  construction  of  the  organs  themselves. 

The  nervous  system  has  been  endowed  with  peculiar  proper- 
ties or  powers,  in  order  that  it  may  be  the  seat,  and  the  instru- 
ment, of  mental  acts.  These  mental  acts,  and  all  the  functions 
in  which  they  bear  a  necessary  share,  constitute,  according  to 
Dr.  Alison,  the  animal  life,  or  animal  functions.  As  in  all  ani- 
mals the  reception  of  food  into  the  digestive  organs,  and  as,  in 
all  vertebrated  animals,  and  many  of  the  inferior  orders,  in  the 
adult,  the  reception  of  air  into  the  respiratory  organs  is  accom- 
plished by  movements  which  are  excited  through  the  intervention 
of  sensations  and  of  instincts  and  volitions  ;  he  considers  the 
commencement  of  the  processes  of  respiration  and  digestion  in 
them  as  belonging  to  the  province  of  animal  life,  and  as  dependent 
on  the  nervous  system.  Dr.  Alison,  thei'cfore,  commences  his 
account  of  the  animal  functions,  with  the  consideration  of  res- 
piration, animal  heat,  and  digestion,  which  he  refers  to  that 
class :  proceeding  afterwards  to  notice  the  physiology  of  the 
external  senses,  of  the  mental  faculties,  voluntary  and  instinctive 
motion,  the  involuntary  action  of  the  mind  on  the  body,  sleep  and 
the  analogous  states  of  somnambulism,  reverie,  and  other  irre- 
gular actions  of  the  nervous  functions.  The  subjects  of  genera- 
tion, and  the  pecuharities  of  age,  sex,  and  temperament,  occupy 
the  concluding  chapters  of  his  work.  <; 

87.  The  order  in  which  Mr.  Mayo  has  treated  of  the  func- 
tions,* differs  but  little  from  that  adopted  by  Dr.  Alison. 

88.  The  author  has  given,  in  his  Bridgewater  Treatise,-]  an 
arrangement  of  the  functions  founded  altogether  on  the  basis  of 
final  causes:  and  corresponding  therefore  with  the  views,  which 
have  been  explained  in  the  preceding  chapter,  of  the  relative 
subordination  of  purposes  which  the  functions  are  designed  tO' 
answer  in  the  economy;  and  not  limited  to  human  physiology, 
but  embracing  all  the  difierent  forms  and  modifications  which 
those  functions  present  in  the  animal  kingdom.  Taking  them  in 
the  order  of  their  increasing  complexity,  he  has  distribuied  them 
into  the  four  following  classes;  namely, 

FirsUX\\Q  mechanical  functions, which  include  the€onsideration 
of  all  the  circumstances  relating  to  the  mechanism  of  the  frame 
and  of  its  different  organs ;  the  arrangements  provided  for  pro- 
curing the  pi'oper  cohesion,  strength  and  mobility  requisite  for 
the  drtferent  actions  they  have  to  perform  ;  and  also  for  the  pre- 
servation of  their  connexions,  support,  security  and  other  me- 
chanical conditions  adapted  to  the  exercise  of  their  respective 

*  Outlines  of  Human  Physiology,  3d  edition,  London,  1833.  [4th  edit. 
Lond.  1837.] 

I  Roget,  Animal  and  Vegetable  Physiology,  considered  with  reference  to 
Natural  Theology,  2  vols.  London,  1834.     [Philad.  1836.] 


56  PHYSIOLOGY. 

functions.  To  this  head  are  also  referred  the  operation  of  the 
moving  powers,  derived  principally  from  muscular  contractility, 
by  which  the  various  parts  of  this  system  of  machinery  are  set 
in  motion. 

Secondly,  the  nutritive,  or  chemical  functions,  corresponding 
to  w|iat  has  been  formerly  denominated  the  vital  functions ;  and 
the  object  of  which  is  the  preservation  of  the  organs  in  those 
states  of  chemical  composition,  which  enable  them  to  sustain 
life,  and  to  perform  their  destined  offices  in  the  economy.  The 
functions  by  which,  in  the  higher  orders  of  animals,  this  object 
is  accomplished,  may  be  arranged  under  the  following  heads  ; 
each,  however,  admitting  of  further  subdivision.  1.  Assimilation,- 
including  the  processes  which  prepare  the  food  for  digestion — 
chymijication,  which  is  the  office  of  the  stomach,  and  chylijication, 
which  is  performed  in  the  intestines.  2.  Lacteal  absorption,  by 
which  the  chyle,  so  prepared,  is  collected  into  the  heart  and 
blood-vessels.  3.  Circulation,  by  which  the  blood,  or  nutrient 
fluid,  is  regularly  diffijsed  over  the  system.  4.  Respiration,  or 
the  aeration  of  the  blood.  5.  Secretion,  by  which  the  properties 
of  that  fluid  are  modified.  6.  Excretion,  by  which  various 
chemical  principles  are  separated  from  the  blood,  and  discharged 
from  the  system.  7.  Absorption,  by  which  substances  are  con- 
veyed from  different  parts  back  again  into  the  general  mass  of 
circulating  fluids.  8.  Nutrition,  by  which  the  nutritive  matter 
is  applied  to  the  growth  or  restoration  of  the  various  organs  of 
the  body,  so  as  to  maintain  them  in  the  state  which  enables  them 
to  discharge  their  proper  functions.  9.  For  effecting  all  these 
various  processes,  the  agency  of  a  peculiar  power,  derived  from 
the  properties  of  the  nervous  system,  is  requisite.  This  may  be 
termed  the  nervous  jjower,  in  contradistinction  to  those  actions 
of  the  same  system,  which  have  reference  to  mental  phenomena, 
and  which  come  under  the  next  class  of  functions. 

Thirdly,  the  sensorial  functions  comprehend  all  those  corporeal 
changes  in  which  the  mind  is  concerned ;  and  consequently  in- 
clude those  of  sensation,  of  perception,  of  volition,  and  all  those 
intellectual  functions,  which  employ  for  their  agency  the  physical 
organization  of  the  body. 

Fourthly,  the  reproductive  functions,  which  have  for  tfieir 
object  the  continuance  of  the  species,  and  the  multiplication  of 
its  numbers.  This  subject  is  naturally  connected  with  the  pro- 
gressive development  of  the  organs,  the  growth  of  the  body  from 
infancy  to  manhood  ;  and  the  stages  of  its  decline,  till  all  the  vital 
phenomena  cease  by  the  death  of  the  individual. 


THE    VITAL    POWERS.  57 


CHAPTER   IV. 


THE     VITAL    POWERS. 


89.  We  have  already  remarked,  that  there  are  two  ways  in 
which  the  assemblage  of  phenomena  presented  to  us  by  living 
beings  may  be  studied.  We  may,  in  the  first  place,  view  these 
as  mere  physical  phenomena,  applying  to  them  the  same  methods 
of  induction  which  have  been  employed  with  so  much  success 
in  other  departments  of  natural  science.  The  object  of  philo- 
sophical induction  is  the  reference  of  the  events  occurring  in 
nature  to  their  proper  causes.  This  is  accomplished  by  compar- 
ing the  phenomena  together,  observing  in  what  they  agree,  and 
in  what  they  differ,  classing  them  in  the  order  of  their  agreement ; 
and  distinguishing  them  according  to  their  differences.  The 
result  of  this  process,  when  it  has  been  carried  as  far  as  the 
extent  of  our  mass  of  facts  will  allow,  is  the  establishment  of 
certain  general  relations  between  these  facts,  orconditions,  under 
which  they  occur,  and  which  we  may  consider  as  so  many  laios 
of  nature ;  and  any  appearance  we  may  afterwards  meet  with 
which  corresponds  in  its  character  to  any  single  law,  or  com- 
bination of  these  laws,  is  at  once  referred  to  them,  and  considered 
as  a  particular  instance  or  exemplification  of  these  laws.  When 
we  can  succeed  in  tracing  these  coincidences  with  a  previously 
established  law  or  general  fact,  we  are  said  to  have  discovered 
its  cause.  Philosophy,  in  this  sense,  then,  comprehends  the  col- 
lection and  comparison  of  phenomena,  their  classification,  the 
establishment  by  careful  induction  of  general  laws;  the  verifica- 
tion of  these  laws  by  experiment;  and  lastly,  the  subsequent 
reference  of  particular  phenomena  to  their  appropriate  laws. 

90.  In  the  sciences  which  relate  to  the  laws  of  matter  in  its 
inorganic  state,  this  inductive  method  of  philosophising  admits  of 
being  pursued  to  an  indefinite  extent,  and  v^'ith  comparative 
facility.  The  phenomena  themselves,  which  are  the  subjects  of 
induction,  are  of  a  simple  and  more  definite  character  than  those 
of  animal  or  vegetable  life  ;  they  are  generally  more  under  our 
control;  and  more  easily  subjected  to  the  test  of  experiment. 
The  endless  variety  of  the  forms  of  life,  the  extent  and  intricacy 
of  the  connexions  between  the  different  parts  of  the  animal  system, 
introduce  a  degree  of  complexity  in  the  phenomena,  incomparably 
greater  than  is  ever  met  with  in  the  combinations  of  inorganic 
matter.     We  shall  accordingly  find  that  the  knowledge  we  have 


58  PHYSIOLOGY. 

hitherto  acqmred  of  the  physical  laws  which  govern  the  vital 
phenomena,  is  as  yet  exceedingly  imperfect. 

91.  In  entering  upon  the  philosophical  study  of  the  phenomena 
presented  to  us  in  the  living  body,  and  carefully  arranging  them 
according  to  the  rules  of  induction,  and  without  reference  to  the 
final  causes  that  connect  them,  (a  subject  which  forms  a  totally 
different  branch  of  inquiry,)  we  easily  recognize  the  operation  of 
many  of  those  powers  and  principles  to  which  inorganic  matter 
is  also  subjected.  The  living  system,  with  all  its  complicaied 
apparatus  of  solids  and  fluids,  is  obedient  to  the  universal  laws 
of  gravitation,  of  cohesion,  of  elasticity,  of  capillary  attrac- 
tion, &c.,  as  well  as  toHhe  ordinary  principles  of  mechanics, 
hydrostatics,  hydraulics,  and  pneumatics,  which  result  from  com- 
binations of  these  laws  ;  and  we  may  pursue  the  application  of 
these  laws  to  the  mechanism  of  the  body,  as  far  as  no  other 
causes  intervene,  without  danger  of  error. 

92.  The  laws  of  chemistry  apply  also,  to  a  certain  extent,  to 
the  changes  which  are  going  on  in  the  living  system  :  but  in 
tracing  the  operation  of  these  laws,  we  soon  become  sensible  of 
the  apparent  interference  of  other  principles  which  seem  to  control 
the  ordinary  chemical  aflinities  which  the  same  kinds  of  matter 
are  found  to  exert  when  deprived  of  life.  Here,  then,  we  per- 
ceive a  sensible  deviation  from  the  course  of  phenomena  exhibited 
by  inorganic  matter ;  and  we  are  forced  to  recognize  the  exist- 
ence of  new  and  unknown  powers  pecuhar  to,  and  characterizing 
the  living  state.  We  discern  the  operation  of  such  powers  in  the 
processes  of  digestion,  of  sanguification,  of  nutrition,  of  secretion, 
of  the  growth  and  organization  of  the  various  structures  that 
compose  the  fibres  of  the  body.  Powers  of  a  similar  kind  are 
exhibited  in  the  phenomena  of  vegetation:  they  seem,  therefore, 
to  attach  to  vitality  in  all  its  forms.  In  order  to  distinguish  them 
from  the  ordinary  chemical  affinities  to  which  they  are  so  fre- 
quently opposed,  we  shall  designate  them  by  the  name  of  Or- 
ganic Affinities,  although,  as  we  shall  afterwards  attempt  to 
show,  they  probably  do  not  differ  in  their  kind,  but  only  in  the 
circumstances  and  conditions  of  action,  from  the  ordinary  inor- 
ganic affinities. 

93.  Another  power  which  more  peculiarly  appertains  to  animal 
fife  is  Contractility.  This  is  especially  a  property  of  those  fibres 
which  compose  the  muscles.  It  is  often  denominated  Irritability, 
a  name  originally  given  to  it  by  Glisson,  but  which  has  justly 
been  objected  to  by  Dr.  Bostock  as  a  term  employed  in  many  dif- 
ferent senses,  according  as  it  is  applied  in  physiology,  pathology, 
or  ethics.  Haller  speaks  of  it  frequently  under  the  designation 
of  the  Vis  insita.  The  term  Contractility,  adopted  by  Dr.  Bos- 
tock,* and  sanctioned  by  many  other  eminent  physiologists,  is  in 

*  Elementary  System  of  Physiology,  third  edition,  pp.  91,  92. 


THE    VITAL    POWERS.  59 

itself  unobjectionable,  and  has  the  advantage  of  being  a  simple 
expression  of  the  fact  itself.  It  consists  in  the  spontaneous  short- 
ening of  muscular  fibres,  in  consequence  of  the  impression  of 
certain  agents  termed  stimuli,  by  a  power  residing  in  the  fibres 
themselves,  and  which  operates  with  a  force  greatly  superior  to 
any  of  the  ordinary  mechanical  sources  of  motion. 

94.  The  remarkable  property  which  the  nerves  possess  of  con- 
veying with  electric  celerity  impressions  made  on  one  of  their 
extremities,  or  even  on  any  part  of  them,  to  the  opposite  ex- 
tremity, and  to  other  parts  in  the  line  of  their  course,  the  influ- 
ence of  which  impressions  are  rendered  apparent  by  certain 
etiects,  such  as  the  contraction  of  the  muscles,  increased  or 
modified  action  of  the  blood-vessels,  absorbents,  and  organs  of 
secretion,  and  the  evolution  of  animal  heat.  All  these  effects 
may  take  place  from  impressions,  or  irritations,  (by  which  term 
is  meant  impressions  of  a  certain  degree  of  intensity,)  which  do 
not  excite  sensation,  or  volition,  or  any  other  mental  change; 
and  they  even  occur  after  the  destruction  or  removal  of  those 
parts  of  the  nervous  system  which  are  connected  with  affections 
of  the  mind.  A  power  of  the  same  kind  is  also  possessed  by 
those  nerves  which  are  connected  with  the  sensorium,  on  the 
parts  in  immediate  connexion  with  the  sentient  principle. 

95.  It  is  by  the  exertion  of  this  power  that  impressions  made 
on  those  nervous  filaments  which  are  instrumental  in  sensation, 
and  especially  if  made  on  their  extremities  which  are  distributed 
to  the  organs  of  the  external  senses,  are  instantly  transmitted  to 
the  sensorium,  in  which  they  may  be  said  to  terminate,  and  the 
changes  produced  in  which  are  attended  by  the  mental  affection 
termed  sensation.  In  like  manner,  certain  other  changes  in  the 
sensorium,  consequent  on  volition,  which  is  a  mental  affection, 
are  followed  by  the  contraction  of  certain  muscles,  by  means  of 
some  unknown  influence  communicated  through  the  medium  of 
certain  other  nervous  filaments  having  their  origin  in  the  senso- 
rium, and  their  termination  in  those  muscles.  The  nature  of  the 
power  by  which  these  transmissions  are  effected  in  the  course  of 
each  of  these  sets  of  nervous  filaments,  judging  from  the  simi- 
larity of  the  circumstances  under  which  it  takes  place,  especially 
in  the  instantaneousness  of  the  effect,  is  probably  the  same  in 
every  case ;  the  only  perceptible  difference  in  the  mode  in  which 
it  is  exerted  consisting  in  the  direction  of  the  transmission.  This 
remarkable  power,  which  is  totally  distinct  from  any  mental 
effort  that  may  accompany  its  exertion,  we  shall  distinguish  by 
the  name  of  the  nervous  jjower. 

96.  A  fourth  power,  perfectly  distinct  from  any  of  the  former, 
although  it  also  belongs  to  a  portion  of  the  nervous  system,  is 
that  from  which  the  corporeal  changes  which  take  place  in  those 
parts  immediately  connected  with  sensation,  volition,  and  the 


60  PHYSIOLOGY. 

intellectual  operations,  proceed.  To  this  specific  property,  which 
should  be  carefully  distinguished  from  the  mere  faculty  of  trans- 
mission possessed  by  the  fibres  of  the  nerves,  the  name  of  senso- 
rial poioer  has  been  given.  We  are  indebted  to  Dr.  Wilson 
Philip  for  the  establishment  of  this  important  distinction  in  the 
specific  powers  of  the  nervous  system,  and  for  having  bestowed 
upon  it  the  above  appropriate  designation.  The  same  term  had, 
indeed,  been  employed  by  physiologists  in  a  different  and  much 
more  extended  sense,  as  including  muscular  irritability,  which 
had  been  regarded  as  in  some  way  or  other  analogous  to  nervous 
power.  In  the  sense  in  which  we  shall  use  the  term,  it  is  meant 
to  apply  exclusively  to  those  physiological  changes  occurring  in 
certain  parts  of  the  nervous  system,  which  produce  or  accom- 
pany changes  or  affections  of  the  mind. 

97.  It  is  evident  that  the  astonishing  properties  belonging  to 
the  refined  organization  of  the  brain,  which  constitute  sensorial 
power,  and  which  are,  in  a  manner  utterly  incomprehensible  to 
us,  connected  with  the  affections  of  the  sentient  and  intelligent 
principle,  present  subjects  of  far  higher  interest  than  even  the 
organic,  muscular,  or  nervous  powers,  and  are  infinitely  more 
remote  from  the  ordinary  attributes  of  matter. 

98.  Thus  we  may  perceive  that  the  system  of  the  living  body 
exhibits  not  only  a  multiplicity  of  new  powers,  which  we  no 
where  meet  with  in  unorganized  matter,  but  also  presents  us 
with  a  gradation  of  powers  ascending  from  those  of  a  mecha- 
nical nature,  but  yet  derived  from  a  highly  artificial  arrangement 
of  particles,  to  those  of  a  refined  and  elaborate  chemistry  silently 
at  work  in  the  secret  laboratories  of  the  body ;  rising  again  to 
principles  of  a  still  more  elevated  order,  acting  through  the  me- 
dium of  the  nerves  ;  till  we  lose  ourselves  in  the  more  lofty  con- 
templation of  those  mysterious  agencies,  which  confer  on  the 
central  portions  of  the  nervous  system  the  power  of  exciting 
sensation ;  which  render  them  instruments  of  thought  and  of 
volition,  and  which  stamp  on  the  being  they  compose  the  distinc- 
tive character  of  individuality. 

99.  Viewed  with  reference  to  their  subserviency  to  final  causes, 
it  is  to  the  sensorial  powers,  which  confer  the  capacity  of  enjoy- 
ment, that  the  supreme  rank  in  point  of  importance  must  be  as- 
signed. The  faculties  of  sensation,  of  voluntary  motion,  and  of 
enjoyment,  are  the  only  ultimate  ends  for  which,  as  far  as  we  can 
judge,  the  animal  has  been  created  and  endowed  with  life.  Those 
ultimate  ends  of  its  being  are  attained  primarily  by  the  sensorial 
powers ;  and  to  the  maintenance  of  these  are  the  muscular  and 
the  nervous  powers  subservient.  Of  these  latter  powers  it  is 
also  evident  that  the  muscular  is  placed  in  obedience  to  the 
nervous,  in  the  same  manner  as  the  nervous  is  obedient  to  the 
sensorial  power.     Thus,  the  views  now  presented  of  the  classifi- 


THE    VITAL    POWERS.  61 

cation  and  distribution  of  the  physical  powers  which  operate  in 
producing  the  phenomena  of  hfe,  are  in  strict  accordance  and 
harmony  with  the  results  obtained  from  the  consideration  of  final 
causes,  which  we  have  already  presented  in  our  preliminary 
chapter. 

100.  If  the  analysis  we  have  here  offered  of  the  vital  powers, 
that  is,  of  powers  peculiar  to  the  phenomena  of  life,  and  the  dis- 
tinctions we  have  endeavoured  to  establish  between  them  be 
correct,  we  shall  be  enabled  at  once  to  detect  the  fallacy  of  those 
views  of  life,  and  of  those  definitions  of  the  vital  principle  which 
are  generally  received  ;  and  which,  we  apprehend,  have  been 
laid  down  in  violation  of  the  just  rules  of  philosophical  induction. 
The  truth  is,  disguise  it  how  we  may  by  a  vain  parade  of  words, 
the  real  state  of  the  science  is  not  sufficiently  advanced  to  authorise 
that  degree  of  generalization  which  these  definitions  would  imply. 
We  are  certainly  not  warranted,  by  the  phenomena  already 
known,  in  regarding  life  as  the  effect  of  any  sins;le  power.  The 
attempt  of  Brown,  of  Hunter,  and  of  Bichat  to  reduce  the  science 
to  this  state  of  simplification,  though  highly  ingenious,  are  yet 
premature ;  and  have,  it  is  to  be  feared,  had  rather  the  effect  of 
retarding  than  of  advancing  the  progress  of  real  science. 

101.  Many  of  the  older  physiologists  entertained  the  notion  of 
a  principle,  endowed  with  qualities  in  some  measure  partaking 
of  intelligence,  and  as  if  it  were  a  spirit  presiding  over  and 
governing  the  vital  actions.  Such  was  the  idea  attached  by 
Van  Halmont,  and  by  Stahl,  to  the  principle  which  they  termed 
the  archceus,  or  anima,  and  which,  they  conceived,  regulated  the 
operations  of  the  different  powers  of  the  system ;  an  assumption 
which,  however,  naturally  suggesting  itself  to  the  mind,  while 
contemplating  the  harmonious  adjustments  that  pervade  every 
part  of  the  animal  economy,  is  in  no  respect  a  philosophical  ex- 
planation of  the  phenomena,  and  is  even  utterly  irreconcilable 
with  some  of  these  phenomena.  In  like  manner,  the  vis  medi- 
catrix  natures,  which  Hoffman  and  Cullen  have  so  largely 
employed  in  their  pathological  theories,  and  which  supplied  them 
with  ready  solutions  of  every  obscure  morbid  change  that  em- 
barrassed them,  was,  in  fact,  nothing  more  than  a  branch  of  the 
same  doctrine.  Nor  have  the  more  sober  theorists  of  modern 
times  been  sufficiently  on  their  guard  against  this  illusion.  In 
the  attributes  which  John  Hunter  ascribes  to  his  mtal  'principle, 
we  may  continually  trace  the  same  want  of  discrimination  between 
that  intelligence,  by  which  the  conditions  of  organization  were 
originally  adjusted  to  a  variety  of  contingent  circumstances,  and 
those  physical  agents,  by  the  instrumentality  of  which  the  intended 
objects  are  attained.  When  it  is  said,  for  example,  in  the  language 
of  this  school,  that  the  coagulation  of  the  blood  is  occasioned  by 
"  the  stimulus  of  necessity,"  it  is  clearly  the  final  cause  alone 

6 


62  PHYSIOLOGY. 

which  is  indicated,  while  the  real  physical  cause  is  not  assigned; 
and  it  is  also  evident  that  no  advance  is  thereby  made  towards 
its  discovery.  This  pi^inciiole  of  life,  with  which  organized 
beings  are  endowed,  is  represented  as  a  new  power,  which 
modifies  and  controls  the  operation  of  those  simpler  physical 
laws,  to  which  the  same  matter,  in  its  unorganized  slate,  is  sub- 
jected; a  power  which  imposes  new  cohesive  and  repulsive  forces 
on  the  solid  materials  of  the  animal  or  vegetable  structures,  which 
imparts  to  the  fiuids  a  new  property  of  coagulation,  which  alters 
the  order  of  chemical  affinities  between  their  elements  or  primary 
compounds,  retaining  them,  contrary  to  their  natural  tendencies, 
in  a  certain  state  of  equilibrium,  and  resisting  the  agency  of 
causes  usually  tending  to  destroy  that  state :  and,  lastly,  which 
produces,  in  a  degree  corresponding  with  the  wants  of  the  system, 
either  an  evolution  or  an  absorption  of  caloric.  All  these,  it 
must  be  admitted,  are  purposes  of  manifest  utility,  being  directly 
conducive  to  the  welfare  of  the  individual,  and  indeed  essential 
to  its  continuance  in  the  living  state.  In  as  far  as  they  are 
means  conducive  to  specific  ends,  the  reference  of  all  these 
phenomena  to  one  class  cannot  be  objected  to.  The  fallacy  lies 
in  regarding  it  as  a  philosophical  generalization  of  effects  of  a 
similar  kind,  resulting  from  the  operation  of  a  simple  power  in 
nature  ;  for  between  many  of  these  effects,  considered  as  mere 
physical  phenomena,  there  exists  not  the  remotest  similarity. 
But  it  is  the  fundamental  principle  of  the  method  of  induction, 
that  similar  effects  alone  are  to  be  ascribed  to  the  agency  of  the 
same  physical  cause.  Judging,  therefore,  from  the  observed  effects, 
which  differ  widely  in  their  nature  from  each  other,  we  ought 
to  infer  the  operation  of  several  distinct  powers,  the  concurrence 
of  which  is  requisite  to  produce  the  complex  phenomena  in  ques- 
tion. We  are,  no  doubt,  unavoidably  led  to  view  these  phenomena 
as  conjoined,  because  we  witness  their  existing  combinations, 
and  perceive  that  they  are  tending  to  the  accomplishment  of  a 
specific  purpose  ;  namely,  the  preservation  and  welfare  of  the 
being  to  which  they  relate.  But  this  unity  of  design  is  an  at- 
tribute, not  of  matter,  but  of  intellect,  and  does  not  necessarily 
imply  the  unity  of  the  agent  employed  in  their  production. 

102.  We  m.ay  take,  as  an  example,  the  phenomena  of  the  cir- 
culation of  the  blood,  which,  when  viewed  with  relation  to  that 
function,  form  together  so  beautiful  and  harmonious  a  system. 
These  phenomena,  taken  abstractedly,  are  ultimately  resolvable 
into  such  as  result  from  a  few  general  powers,  as  muscular  con- 
tractility, membranous  elasticity,  the  hydrauhc  properties  of  the 
blood,  &c.  The  phenomena  of  digestion,  in  hke  manner,  when 
subjected  to  analysis,  are  found  to  be  results  of  the  combined 
agencies  of  the  muscular  action  of  the  stomach  and  intestines,  of 
the  chemical  powers  of  the  gastric  juice,  the  bile,  &c.  of  the 


THE    VITAL    POWERS.  63 

organic  powers  of  secretion,  and  so  forth  ;  all  of  which  concur 
in  the  production  of  a  definite  object,  namely,  the  conversion  of 
the  aliment  into  chyle.  The  combined  processes  subservient  to 
this  purpose,  constitute,  when  viewed  in  their  relation  to  final 
causes,  the  function  of  digestion. 

103.  However  the  laws  which  regulate  the  vital  phenomena 
may  appear,  on  a  superficial  view,  to  differ  from  those  by  which 
the  physical  changes  taking  place  in  inorganic  matter  are  gov- 
erned, still  a  more  profound  investigation  of  their  real  character 
will  show  that,  when  viewed  abstractly  from  the  consideration  of  , 
final  causes,  there  is  really  no  essential  difference  between 
them,  either  as  to  their  comprehensiveness,  their  uniformity  of 
action,  or  the  mode  in  which  they  are  to  be  established  by  the 
generalization  of  particular  facts.*  The  difficulty  of  effecting 
these  inductive  generalizations  is  undoubtedly  incomparably 
greater  in  the  former  than  in  the  latter;  but  this  difficulty  is 
similar  to  that  which  impedes  our  progress  in-all  cases  wfiere  the 
existing  combinations  which  are  the  objects  of  study,  are  too 
numerous  and  too  complicated  to  yield  to  our  powers  of  analysis. 
We  have  examples  of  this  difficulty  in  many  branches  of  physical 
science ;  in  meteorology,  for  example,  where  no  one  can  doubt  that 
the  phenomena  are  the  results  of  the  ordinary  physical  powers, 
of  the  laws  of  which  we  are  tolerably  cognisant ;  but  the  opera- 
tions of  which,  in  effecting  the  daily  and  hourly  changes  of  atmos- 
pheric phenomena,  have  hitherto  bafffed  the  most  persevering  and 
penetrating  inquiries  directed  to  this  highly  important  branch  of 
physics.  There  is,  in  like  manner,  no  distinct  evidence  of  the 
material  particles,  which  compose  the  organized  and  living  fabric 
being  actuated  by  any  powers  or  principles  different  from  those 
which  are  inherent  in  them,  in  their  ordinary  or  inanimate  state. 
They  are,  in  both  cases,  obedient  to  certain  definite  physical  laws, 
the  operation  of  which  is  determined  by  the  peculiar  circumstances 
of  their  mode  of  combination,  and  the  peculiar  conditions  under 
which  they  are  brought  into  action. 

104.  It  may,  in  like  manner,  be  contended,  that  the  affinities 
which  hold  together  the  elements  of  living  bodies,  and  which 
govern  the  elaboration  of  organic  products,  are  the  same  with 
those  which  preside  over  inorganic  compounds;  and  that  the 
designations  of  organic  and  vital  affinities  are  expressive  only  of 
peculiarities  attending  the  circumstances  and  conditions  under 
which  they  are  placed,  but  do  not  imply  any  real  difference  in 
the  nature  of  the  powers  themselves.  If  our  knowledge  of  these 
circumstances  and  conditions  were  complete,  their  identity  would 
be  at  once  revealed  to  us  ;  but  until  that  period,  which  must  be 

*  See  an  Essay  by  Mr.  Carpenter  on  the  difference  of  the  Laws  regulating 
Vital  and  Physical  Phenomena,  Edinburgh  New  Philosophical  Journal,  xxiv. 
337. 


64  PHYSIOLOGY. 

very  far  distant,  has  arrived,  we  must  be  content  with  gathering 
a  few  indications,  which  occasionally  break  out  from  the  clouds 
of  mystery  in  which  the  subject  is  obscured,  of  the  similarity  of 
operation  between  these  two  apparently  contending  powers,  the 
ordinary  cl  emical,  and  the  extraordinary  vital  affinities.  Every 
fresh  discovery  in  animal  and  vegetable  chemistry,  by  showing 
the  mutual  convertibility  of  many  of  the  proximate  principles  of 
organic  compounds,  adds  to  the  number  of  those  indications. 
Hence  it  becomes  every  day  more  and  more  probable  that  the 
forces  immediately  concerned  in  the,  production  of  chemical 
changes  in  the  body,  are  the  same  as  those  which  are  in  constant 
operation  in  the  inorganic  world  ;  and  that  we  are  not  warranted 
in  the  assertion  that  the  operations  of  vital  chemistry  are  directed 
by  distinct  laws,  and  are  the  results  of  new  agencies. 

105.  We  are  therefore  led  to  the  conclusion,  that  the  vital 
properties  are  not,  as'  it  is  commonly  expressed,  superadded  to 
matter  in  the  process  of  organization,  but  are  the  result  of  the 
material  constitution,  that  is,  of  the  peculiar  combinations  and 
arrangement  of  the  ultimate  molecules  of  the  organised  tissues, 
which  call  out  and  develop  the  properties  previously  existing 
in  those  molecules,  but  which  cannot  be  effective  unless  these 
circumstances  exist. 

106.  However  natural  it  may  be  to  conceive  the  existence  of 
a  single  and  presiding  principle  of  vitality,  we  should  recollect 
that  this  in  the  present  state  of  our  knowledge,  is  only  a  fiction 
of  the  mind,  not  warranted  by  the  phenomena  themselves,  in 
which  we  perceive  so  much  real  diversity,  and  therefore  inadmis- 
sible as  the  result  of  philosophical  induction.  We  find,  that 
vitality  ceases  in  different  textures,  at  different  periods,  prior  to 
the  total  extinction  of  life  ;  a  phenomenon  which  appears  scarcely 
compatible  with  the  unity  of  any  such  power. 

107.  It  is  w^ell  known  that  attempts  have,  in  like  manner,  from 
time  to  time  been  made  to  reduce  the  phenomjcna  of  the  inorganic 
world  to  a  single  primordial  law ;  instead  of  being  content  to 
refer  them  to  'the  Operation  of  distinct  laws,  such  as  those  of 
gravitation,  cohesion,  elasticity,  light,  heat,^electricity,  magnet- 
ism, and  chemical  affinity.  The  phenomena  usually  ascribed  to 
these  great  powers  of  nature  have,  for  instance,  been  considered 
as  resolvable  into  one  universal  principle  of  attraction.  By  other 
philosophers  they  have  been  regarded  as  the  effects  of  a  general 
and  sole  power  of  repulsion.  None  of  these  simplifications  are 
as  yet  warranted  by  facts ;  and  equally  vain,  in  the  present  state 
of  the  science,  is  the  endeavour  to  reduce  all  the  vital  phenomena 
to  one  single  law.  It  is  possible,  or  perhaps  even  probable,  that 
future  researches  may  be  successful  in  establishing  the  identity 
of  some  of  the  powers  we  now  conceive  to  be  distinct,  with 
other  powers  already  known.     Thus,  in  the  physical  sciences, 


THE    VITAL    POWERS.  65 

the  recent  discoveries  that  have  taken  place  in  electro-magnetism, 
have  satisfactorily  established  the  identity  of  the  magnetic  and 
electric  agencies.  The  same  may  possibly  be  accomplished  in 
future  times,  with  regard  to  heat  and  light,  which  are  already 
connected  together  by  so  many  analogies.  But  no  such  approxi- 
mation can  yet  be  attempted  with  any  prospect  of  success, 
between  the  muscular,  the  nervous,  the  sensorial,  and  the  ofganic 
powers.  No  speculative  ingenuity  can  reduce  them  to  a  single 
physical  power;  nor  can  we  establish  any  kind  of  association 
between  them,  but  by  the  consideration  of  another  and  a  totally 
different  class  of  relations,  namely,  those  they  bear  to  the  general 
object  which  they  combine  to  produce.  This,  however,  is  to 
substitute  final  for  physical  causes ;  a  mode  of  procedure,  which, 
we  have  seen,  is  totally  at  variance  with  the  principles  of  philo- 
sophical induction.  Physical  causes  only  are  the  legitimate 
objects  of  philosophical  analysis,  and  the  true  bases  of  the  physi- 
cal sciences. 

108.  We  shall  now  proceed  to  give  an  account  of  each  sepa- 
rate function ;  taking  them  in  the  order  of  their  respective 
simplicity,  with  reference  not  only  to  their  objects,  but  also  to 
the  powers  which  are  concerned  in  their  accomplishment. 

109.  We  shall  accordingly  begin  with  the  consideration  of  the 
mechanical  functions,  as  being  more  simple  in  their  character, 
and  implying  the  operation  of  the  simpler  powers  of  organiza- 
tion; together  with  the  peculiar  faculty  of  muscular  contractihty, 
which  is  the  great  source  of  mechanical  power  provided  for 
carrying  on  the  greater  movements  of  the  machine.  We  shall, 
in  the  second  place,  review  that  class  of  functions  which  depend 
more  especially  on  the  operation  of  the  organic  affinities,  and 
which  have  for  their  objects  the  nutrition  and, extension  of  the 
organs,  and  their  maintenance  in  that  state  of  chemical,  as  well 
as  mechanical  condition,  which  fits  them  for  the  performance  of 
their  respective  offices.  We  shall  then  be  properly  prepared  for 
the  study  of  that  higher  class  of  functions,  which  appertain  to  sen- 
sation,^nd  all  the  other  faculties  connected  with  mind;  functions 
which  imply,  in  addition  to  all  the  powers  concerned  in  the  prece- 
ding functions,  others  of  a  superior  order,  but  which,  although 
in  the  highest  degree  interesting  and  important,  are  incompara- 
bly the  most  obscure  and  complex  of  all.  Our  attention  will,  in 
the  last  place,  be  directed  to  the  functions  relating  to  reproduc- 
tion, the  study  of  which  requires  a  previous  knowledge  of  every 
other  department  of  physiology. 


6* 


66  MECHANICAL    FUNCTIONS. 


CHAPTER  V. 


THE    MECHANICAL    FUNCTIONS. 


Sect.  I. — On  Organization  in  general. 

110.  If  we  analyze  the  ideas  attached  to  the  term  organiza- 
tion, we  find  that  it  implies,  as  its  essential  condition,  a  specific 
arrangement  of  parts,  adapted  to  some  particular  purpose,  and 
composing  by  their  assemblage,  an  individual  system  endowed 
with  life.  It  seems  impossible,  therefore,  to  attach  the  idea  of 
organization  to  a  mere  fluid,  because  the  mechanical  condition 
of  the  particles  of  a  fluid  is  such  as  to  preclude  the  capability  of 
any  permanent  arrangement.  It  appears  to  be  essential  to  every 
organized  structure,  that  there  shall  be  solid  parts  provided  for 
containing  those  which  are  fluid.  All  animal  bodies  accordingly 
are  composed  of  solids  and  fluids  ;  the  former  being  more  perma- 
nent in  their  nature  and  arrangement,  and  constituting  the  basis 
by  which  the  general  form  of  the  body  is  determined  ;  and  the 
latter,  being  lodged  in  appropriate  cavities  formed  by  the  solids, 
but  capable  by  their  mobility  of  undergoing  more  rapid  changes 
of  place,  and  of  chemical  composition. 

ill.  It  may  in -general  be  said,  that  the  solids  bear  but  a 
small  proportion  to  the  fluids,  which  enter  into  the  composition 
of  the  body.  It  is  difficult,  however,  to  determine  the  exact  pro- 
portion which  they  bear  to  one  another ;  in  the  first  place,  be- 
cause this  proportion  is  not  fixed,  and  admits  of  variation  in 
different  agents,  circumstances,  and  conditions  of  the  system  ; 
and,  secondly,  because  it  is  scarcely  possible  to  effect  the  com- 
plete separation  of  these  two  constituent  portions ;  partly  from 
the  ready  conversion  of  the  solids  into  fluids,  and  vice  versa, 
and  partly  from  the  tenacity  of  their  mutual  adhesion.  Some 
estimate  of  this  proportion  has  been  attempted  to  be  formed,  by 
carefully  drying  the  dead  body  in  a  stove,  or  oven ;  and  the  re- 
sult of  some  experiments  has  been,  that  in  an  adult  man,  the 
weight  of  the  fluids  is  to  that  of  the  solids,  as  six  to  one,  or, 
according  to  other  experiments,  as  nine  to  one.  From  the  exa- 
mination of  an  adult  Egyptian  mummy,  which  may  be  supposed 
to  contain  nothing  but  the  dry  fibres  of  the  body,  a  still  lower 
proportion  has  been  assigned  to  the  solid  part;  since  this  mummy 
weighed  only  seven  pounds  and  a  half.* 

*  See  Beclard,  Elemens  de  Anatomic  Generale,  p.  77. 


ORGANIZATION    IN    GENERAL.  07 

112.  The  possibility  of  reducing  all  the  organic  textures  of  the 
human  body  to  one  elementary  material,  which  might  be  regard- 
ed as  the  basis  of  the  whole,  was  long  a  favourite  subject  of 
speculation  among  anatomists:  and  Haller  has  devoted  it  to  the 
first  section  of  his  great  work  on  Physiology.*  He  conceives 
that  all  the  solid  parts  of  the  frame  are  ultimately  composed  of 
fibres ;  the  animal  fibre  being  the  simplest  form  of  organized 
matter,  and  being  to  the  physiologist,  what  the  line  is  to  the 
geometrician,  that  from  which  all  other  figures  are  produced- 
This  simple  fibre,  he  observes,  is  invisible,  even  with  the  assist- 
ance of  the  microscope ;  it  is  only  by  the  union  of  the  primary 
fibres,  that  visible  fibres  are  constituted  ;  and  from  the  assem- 
blage and  lateral  adhesion  of  these,  again,  thin  plates  of  animal 
substance  are  formed,  while  the  grosser  substance  of  the  organs 
themselves,  is  composed  of  a  complicated  contexture  of  these 
plates  and  fibres.f  This  supposed  basis,  or  essential  constituent, 
of  all  animal  textures,  has  been  by  some  termed  the  animal 
■parenchyma,  and,  by  others,  has  been  designated  by  the  general 
name  of  animal  membrane. 

1 13.  Besides  this  spongy  or  areolated  texture,  which  composes 
by  far  the  greater  bulk  of  the  organs  of  the  body,  Haller  has 
also  admitted  two  other  constituent  parts,  namely  the  muscular, 
and  the  nervous  substances.  These  views  have  since  been  gene- 
rally adopted  by  physiologists,  with  some  slight  modifications. 
Many  have  thought  it  necessary  to  introduce,  in  addition  to  the 
preceding,  an  element  which  they  consider  as  of  a  tubular  form, 
constituting  vessels  fitted  to  contain  fluids.  This  was  the  fa- 
vourite doctrine  of  Boerhaave,  who  supposed  that  the  simple 
fibres,  or  the  smallest  into  which  they  can  be  conceived  to  be 
divisible,  formed  by  their  lateral  adhesion,  a  membrane  of  the 
first  order,  which,  when  coiled  up  into  a  tube,  would  constitute 
a  vessel  of  the  first  order.  These  vessels,  again,  when  interwoven 
together,  composed  a  new  order  of  membranes,  by  the  duplica- 
tion of  which  a  second  order  of  vessels  was  formed.  Successive 
series  of  membranes  and  vessels  were  thus  constructed,  until 
they  acquired  a  magnitude  sufficient  to  be  visible  to  the  eye. 
According  to  this  hypothesis,  therefore,  all  the  parts  of  the  body 
might  ultimately  be  resolved  into  a  congeries  of  vessels,  arranged 
in  these  ascending  orders.  This  hypothesis,  which  evidently 
rested  on  the  most  visionary  basis,  has  been  ably  refuted  by 
Albinus,  and  by  Haller.    It  has,  however,  left  some  traces  in  the 

*  Elementa  Physiologriaj  Corporis  Humani. 

t  [The  notion  of  Haller  must  be  regarded  as  a  mere  abstraction;  for  as 
different  animal  substances  are  found  to  be  composed  of  different  proportions 
of  carbon,  hydrogen,  oxygen,  and  azote,  it  is  fair  to  infer  that  the  elementary 
fibre  must  differ  also  in  the  different  structures.  See  Dunglison's  Physiology, 
ij.  36.] 


68  MECHANICAL    FUNCTIONS. 

opinions  expressed  by  many  subsequent  anatomists,  who  still 
cherished  the  idea  of  the  universal  vascularity  of  the  animal 
fabric,  and  of  this  vascularity  being  essential  to  organization. 
The  skilful  injections  of  Ruysch,  who  succeeded  in  introducing 
coloured  fluids  into  vessels,  the  contents  of  which  are  naturally 
transparent,  had  long  ago  shown  that  there  exists  an  order  of 
vessels  too  minute  to  be  otherwise  detected.  Dr.  William  Hunter 
has,  even  in  later  times,  adopted  the  opinion  that  every  living 
part  is  necessarily  vascular;  and  that  where  there  is  no  circula- 
tion, there  can  be  no  life.  Mascagni  was  also  a  strenuous  advo- 
cate of  the  hypothesis  of  the  universal  vascularity  of  the  animal 
textures  ;  but  he  conceived  that  every  part  is  made  up  of  a 
congeries  of  minute  lymphatic  vessels.  We  shall  have  occasion 
afterwards  to  point  out  the  fallacy  of  these  views. 

114.  Although  the  analysis  of  animal  tissues,  into  the  three 
primitive  elements  we  have  pointed  out,  namely,  into  the  mevi- 
hranous,  the  muscular  and  the  nervous  fibres,  be  founded  on  the 
most  prominent  and  well  marked  features  of  distinction  which 
they  exhibit,  yet  there  are  perhaps  other  kinds  of  texture  also, 
which  possess  sufficiently  characteristic  properties  to  entitle  them 
to  rank  as  elementary  tissues ;  these  are  the  alhugineous  fibre 
of  Chaussier,  and  the  epidermoid  substance ;  and  to  these  we 
might  also  add,  in  order  to  make  the  analysis  complete,  the  car- 
tilaginous and  the  osseous  structures. 

115.  But  this  analysis  of  animal  textures,  has,  by  some  later 
anatomists,  been  carried,  in  another  point  of  view,  still  farther. 
With  relation  to  the  forms  assumed  by  the  elementary  tissues, 
they  have  been  referred  to  three  kinds,  the  fibrous,  the  lamellar, 
and  the  granular,  or  globular.  The  two  former  are  exemplified 
in  the  structure  of  the  cellular  substance,  which  composes  the 
greatest  portion  of  the  animal  fabric  ;  the  fibrous  is  characteristic 
of  the  muscular  and  ligamentous  structures;  the  fibrous,  united 
with  the  granular,  is  exhibited  in  the  texture  of  the  glands,  and 
in  the  medullary  substance  of  the  nervous  system;  and  the  globu- 
lar is  most  perfectly  shown  in  the  composition  of  the  chyle,  the 
blood,  and  several  of  the  secretions. 

116.  Anatomists  have  sought  for  still  more  general  results,  by 
means  of  microscopical  investigations.  When  very  high  magni- 
fying powers  are  employed,  both  the  muscular  fibre,  and  the 
nervous  or  medullary  matter,  appear  to  be  resolvable  into  a  mass 
of  globular  particles,  analogous  to  those  which  compose  the 
opaque  portion  of  the  blood.  Meckel  has  founded  upon  these 
observations  the  following  system  :  He  conceives  that  every 
animal  structure  is  ultimately  resolvable  into  two  kinds  of  sub- 
stance, the  one  formed  into  minute,  but  solid  spherular  masses, 
or  globules ;  and  the  other,  being  an  homogeneous,  but  amorphous 
matter,  either  uniting   together  these  globules  in  the  way  of  a 


COMBINATIONS    OF    TEXTURES.  69 

cement  interposed  between  them,  or  constituting  by  itself,  what 
has  been  termed  the  cellular  substance,  membrane,  and  the 
various  structures  derived  from  membrane.  Dr.  Edwards,  on 
the  other  hand,  has  carried  this  notion  to  the  utmost  possible 
length;  for  he  represents  the  cellular  and  membranous  substances, 
as  being  themselves  composed  of  globules ;  so  that,  according 
to  his  views,  the  whole  structure  of  an  animal  body  will  consist  of 
globules. 

But  the  later,  and  more  careful  investigations  of  Dr.  Hodgkin 
and  Mr.  Lister,*  appear  to  have  established,  that  the  globular 
appearance  of  the  different  organized  textures,  when  viewed 
with  microscopes  of  high  magnifying  power,  is  altogether  an 
optical  deception.  A  similar  conclusion,  indeed,  was,  many  years 
ago,  deduced  by  Dr.  Monro,  from  his  microscopical  researches, 
detailed  in  his  work  on  the  Nervous  System. 

Sect.  II. — Combinations  of  Textures. 

H7.  Such  being  the  results  of  the  general  analysis  of  animal 
textures,  into  a  few  primary  elements,  we  are  next  to  consider 
the  combinations  of  these  textures,  which  are  actually  presented 
to  us  by  nature,  in  the  various  organs  of  the  body ;  and  in  order 
to  possess  the  most  comprehensive  views  on  this  subject,  it  will 
be  proper  to  study  these  organs  as  forming  systems  of  which  the 
several  parts  are  related  to  each  other  by  similarity  of  composi- 
tion and  properties.  The  most  elaborate  arrangement,  founded 
on  this  principle,  is  that  of  Bichat,  who  distinguishes  the  constitu- 
ent textures  of  the  body  into  twenty-one  different  kinds.f  But  it 
may  be  objected  to  his  classification,  that  it  is  founded  on  dis- 
tinctions of  function,  as  well  as  on  those  of  structure.  We 
therefore  prefer  following,  on  this  subject,  the  arrangement  of 
Beclard,  which  proceeds  on  one  uniform  principle — namely, 
that  of  mechanical  conformation.  Taking  this  principle  as  our 
guide,  we  shall  find  that  the  systems  of  organs  may  be  easily 
reduced  to  eleven  different  classes:  namely,  1,  the  Cellular; 
2,  the  Adipous ;  3,  the  Membranous ;  4,  the  Dermoid ;  5,  the 
Ligamentous ;  6,  the  Cartilaginous ;  7,  the  Osseous ;  8,  the 
Muscular;  9,  the  Medullary  or  Nervous;  10,  the  Vascular; 
and,  11,  the  Glandular  systems  of  structures.  The  properties 
of  these  several  tissues  will  come  under  our  review  in  connexion 
with  the  functions  to  which  they  are  more  immediately  subser- 
vient. The  three  first  of  these,  however,  claim  our  immediate 
attention,  as  being  the  simplest,  and  most  generally  diffused  over 
the  body. 

*  Philosophical  Magazine,  and  Annals  of  Philosophy,  vol.  ii.  p.  136  ;  and 
also  in  the  appendix  to  their  translation  of  Dr.  Edwards's  work, 
f  See  his  Anatomie  Generule. 


70  MECHANICAL    FUNCTIONS. 


1.   The  Cellular  Texture. 

118.  This  is  the  simplest  form  in  which  the  animal  substance 
presents  itself  to  our  observation  ;  and  it  appears  to  be  not  only 
the  real  basis  of  the  structure  of  all  the  other  organs,  but  also  the 
general  medium  which  unites  their  several  parts  together,  as  well 
as  the  bond  of  connexion  between  adjacent  organs.  It  is,  accord- 
ingly, of  all  the  simpler  textures,  that  which  is  the  most  exten- 
sively diffused  over  the  body;  not  only  pervading  the  substance 
of  the'  organs,  but  also  filling  up  all  the  intervening  spaces,  and 
preserving  them  in  their  proper  relative  situations.  Haller  found 
it  to  consist  of  an  irregular  assemblage  of  plares  and  fibres,  cros- 
sing one  another  in  all  manner  of  directions ;  so  that  when 
stretched  or  expanded  by  the  insinuation  of  any  fluid  between  the 
plates,  the  whole  presents  a  cellular  structure.  These  cells,  which 
are  produced  by  the  separation  of  the  plates  from  each  other, 
are  of  no  regular  shape,  but  communicate  freely  with  one 
another  throughout  the  whole  extent  of  the  substance  in  which 
they  are  met  with. 

119.  As  there  is  a  continuity  of  the  cellular  substance  in  every 
part  of  the  body,  where  it  exists  in  this  form,  there  must,  in  like 
manner,  be  a  continuity  in  the  cavities  of  these  cells ;  and  the 
consequence  of  this  structure  is,  that  any  fluid,  such  as  air,  or 
water,  which  may  happen  to  be  introduced  into  any  one  part, 
will  readily  find  its  way  into  adjoining  parts,  and  will  thus 
gradually  be  diff'used  over  the  whole  body.  If  the  fluid  be  water, 
as  happens  in  dropsies,  it  will,  by  its  gravity,  tend  to  accumulate 
in  the  most  depending  parts  of  the  body,  as  the  ankles,  while  a 
person  is  standing  or  sitting;  and  it  will  leave  these  parts,  and 
be  more  generally  distributed,  after  he  has  remained  for  some 
time  in  a  horizontal  posture. 

The  cellular  texture  may  easily  be  inflated  by  air ;  and  this 
may  happen  in  consequence  of  injury,  even  during  life;  in  which 
case  the  air  gradually  insinuates  itself  into  every  part  of  the 
frame,  pufling  up  the  skin  to  an  extraordinary  degree,  so  as 
totally  to  obliterate  the  features  of  the  face,  and  disfigure  the 
whole  body.  If  measures  be  not  taken  to  let  the  air  escape,  the 
patient  is  at  length  destroyed  by  suflfocation.  A  remarkable 
instance  of  this  disease,  which  is  termed  Emphysema,  is  given 
by  Dr.  William  Hunter,  in  an  essay  on  the  properties  of  the 
cellular  texture,  contained  in  the  second  volume  of  the  Medical 
Observations  and  Inquiries,^  and  which  also  deserves  particular 
notice,  as  presenting  the  best  account  of  this  branch  of  general 
anatomy. 

*  Page  26,  et  seq. 


ADIPOSE    TEXTURE.  71 

120.  The  cells,  or  rather  intervals  between  the  plates  and 
fibres  of  this  substance,  contain  in  the  natural  and  healthy  state, 
a  quantity  of  aqueous  fluid,  which  has  been  termed  the  cellular 
serosity,  and  which  serves  the  purpose  of  lubricating  the  surfaces 
of  the  plates,  and  thus,  by  diminishing  friction,  of  facihtating 
their  relative  motions  on  each  other.  To  this  circumstance  we 
may  also  trace  many  of  the  mechanical  properties  of  the  cellular 
texture ;  such  as  its  perfect  flexibility,  and  its  great  extensibility 
in  various  directions ;  while  it  exerts,  at  the  same  time,  consi- 
derable powers  of  cohesion.  The  combination  of  these  two  latter 
properties  is  the  source  of  another,  which  it  possesses  in  a  very 
eminent  degree,  that  of  Elasticity,  or  the  power  of  recovering 
its  original  form,  when  the  disturbing  force,  whether  producing 
compression  or  extension,  has  ceased  to  act.  It  is  evident  that 
by  possessing  all  these  properties,  the  cellular  texture  is  eminently 
qualified  to  fulfil  the  important  offices  assigned  to  it,  of  serving  as 
the  elastic  scaffolding  or  canvas  for  sustaining  all  the  other 
parts,  and  retaining  them  in  their  proper  situations  ;  and  whilst 
it  is  tlie  universal  mechanical  cement,  or  medium  of  connexion 
between  them,  it  is  at  the  same  time  admirably  adapted  to  faci- 
litate their  relative  movements  and  mutual  actions,  which  are 
required  for  the  performance  of  their  respective  functions. 

121.  Another  property,  besides  elasticity,  has  also  been  ascribed 
to  the  cellular  substance  and  other  textures  derived  immediately 
from  it.  It  consists  in  a  peculiar  kind  of  contractility,  attended 
by  a  sudden  corrugation  and  curling  up  of  its  substance.  As 
this  property  has  been  supposed  to  bear  some  relation  to  muscular 
contractility,  we  shall  defer  its  consideration  till  w^e  come  to  treat 
of  that  property. 

2.  Adipose   Texture. 

122.  This  texture  contains  the  oily  secretion  which  is  known 
by  the  name  of  fat.  The  adipose  matter,  or  fat,  is  lodged  in  par- 
ticular portions  of  the  cellular  texture,  appropriated  to  this  office. 
It  consists  of  very  minute  grains  of  globules,  distinguishable  only 
by  the  aid  of  the  microscope.  Each  of  these  globules  is  con- 
tained in  a  separate  investment,  or  sac,  constructed  of  an  ex- 
ceedingly fine  and  delicate  membrane,  formed  out  of  the  consti- 
tuent plates  of  the  cellular  substance,  and  having  no  external 
opening.  The  size  of  these  vesicles  is  stated  to  be  from  the 
eight-hundredth  to  the  six-hundredth  part  of  an  inch  in  diameter. 
They  are  collected  together  in  small  rounded  masses,  united  by 
vessels,  and  presenting  an  appearance  under  the  microscope,  not 
unlike  that  of  a  bunch  of  grapes.  They  are  lodged  in  the  cells 
of  the  cellular  substance  in  various  situations  throughout  the 
body,  and  contribute  to  fill  up  the  hollows  which  occur  in  difier- 


'    72  MECHANICAL    FUNCTIONS. 

ent  places  between  the  bones  and  muscles,  and  other  organs. 
They  are  very  abundant  immediately  under  the  skin  ;  and  in 
some  parts  are  evidently  interposed  as  cushions  for  the  protec- 
tion of  organs  exposed  to  injury  from  pressure  or  other  mecha- 
nical violence. 

It  is  evident  that  the  cells  in  the  cellular  substance  which  are 
occupied  by  the  fat,  are  different  from  those  which  are  the  seat 
of  dropsical  accumulations  of  fluid  ;  and  that  they  do  not,  like 
the  latter,  communicate  with  one  another;  for  it  is  found  that 
each  portion  of  fat  always  remains  stationary  in  the  same  cell  in 
"which  it  was  originally  lodged. 

12.3.  The  fat  varies  considerably  in  its  consistence  in  diflferent 
.  parts  of  the  body,  according  to  the  purpose  it  is  intended  to  serve. 
At  the  usual  temperature  of  the  living  body,  however,  it  is  retained 
very  nearly  in  a  state  of  fluidity.  The  quantity  accumulated  in 
the  body  is  very  different  at  different  periods  of  life  ;  and  varies 
also  according  to  the  state  of  health,  and  the  peculiar  habit  and 
constitution  of  the  individual.  It  is  whiter  in  its  colour,  and  more 
firm  in  its  consistence,  during  the  earlier  periods  of  life,  and  be- 
comes more  soft,  and  acquires  a  yellow  tinge  as  age  advances. 

124.  The  fat  of  animals  has  been  resolved  by  Chevreul,  who  un- 
dertook an  elaborate  analysis  of  this  substance,  into  two  proximate 
principles,  to  which  he  gives  the  names,  stearin  and  elam. 
The  former,  derived  from  the  Greek  word  o-reag,  signifying  tallow, 
is  of  a  much  more  solid  consistence  than  the  latter  in  ordinary 
temperatures,  and  does  not  melt  under  a  heat  of  from  110°  to 
120°  of  Fahrenheit.  It  is  obtained  from  fat  by  digesting  it  in 
alcohob  in  the  form  of  white  crystalline  needles,  which  are  de- 
posited as  the  fluid  cools.  It  is  a  white  brittle  substance,  void  of 
taste  or  odour,  and  resembling  wax  in  its  appearance.  If,  after 
the  stearin  has  been  deposited,  heat  be  applied  to  the  remaining 
solution,  so  as  to  drive  off  the  alcohol,  there  remains  an  oily 
matter,  which  continues  fluid  at  59°  of  Fahrenheit,  and  is  called, 
by  Chevreul,  elam,  from  the  Greek  term  for  oil,  Imiov. 

The  consistence  of  the  fat  of  different  animals,  and  in  different 
parts  of  the  same  animal,  admits  of  considerable  diversity,  ac- 
cording to  the  proportions  in  which  these  two  ingredients  are 
contained ;  the  abundance  of  stearin  is  the  principal  cause  of  the 
hardness  of  tallow  or  suet,  whilst  an  increased  proportion  of  elain 
characterises  the  composition  of  marrow,  which  is  one  of  the 
most  fluid  kinds  of  fat. 

125.  The  marrow  which  occupies  the  central  cavities  of  the 
cylindrical  bones,  and  which  also  exists  in  small  quantities  in  the 
canals  that  pervade  the  substance  of  the  denser  portions  of  the 
bones,  is  perfectly  analogous  in  its  composition  and  structure  to 
the  fat  in  other  parts  of  the  body.  The  oily  pai'ticles  are  con- 
tained in  membranous  vesicles,  which  are  themselves  connected 


MEMBRANOUS  STRUCTURES.  73 

together,  and  retained  in  their  places  by  a  fine  net- work  of  plates 
and  fibres,  corresponding  to  the  general  cellular  structure  of 
other  parts,  but  of  a  peculiarly  delicate  contexture. 

3.  Membranous  Structures. 

127.  When  the  texture  of  cellular  substance  becomes  consoli- 
dated by  the  intimate  adhesion  of  the  plates  and  fibres  of  which 
it  is  originally  composed,  which,  of  course,  produces  the  complete 
obliteration  of  its  cells,  it  constitutes  the  difl^erent  varieties  of 
membranous  structures.  These  structures  are  of  diffei'ent  degrees 
of  thickness,  and  compose  masses  of  different  degrees  of  density. 
When  expanded  into  a  continuous  sheet  or  plate,  it  forms  what 
is  more  properly  termed  a  membrane.  These  membranes,  when 
sufficiently  thin,  are  semi-transparent,  and  have  a  smooth  and 
uniform  surface.  Haller  found  that  all  membranes  are  resolvable, 
by  long  maceration  in  water,  into  a  flocculenf  spongy  substance, 
in  which  the  original  cells  of  the  cellular  texture  from  which 
they  were  formed,  could  be  rendered  apparent  by  inflating  them 
with  air. 

128.  Membranes  retain  almost  all  the  mechanical  properties 
belonging  to  the  cellular  substance  from  which  they  are  derived  ; 
for  they  are  equally  flexible  and  elastic,  although  possessing 
superior  strength  and  firmness.  But  in  one  respect  they  exhibit 
a  marked  difference,  while  the  simple  cellular  texture,  as  we 
have  seen,  allows  of  the  general  communication  of  fluids  intro- 
duced into  its  cells,  from  one  part  to  another;  membranes  are 
for  the  most  part  impermeable  to  fluids,  and  are  in  consequence 
employed  with  the  express  design  of  preventing  their  ditTusion. 

129.  The  property  possessed  by  membranes  of  contracting 
in  their  dimensions  by  the  evaporation  of  the  water  they  contain, 
and  which  is  united  vwith  the  animal  material  by  a  very  weak 
affinity,  constitutes  what  may  be  termed  the  hygrometric  jiro- 
perty. 

All  the  membranes  are  capable  of  being  dried  by  the  continued 
apphcation  of  a  moderate  heat,  and  may  be  kept  in  this  dry  state 
for  a  great  length  of  time  without  undergoing  any  change.  But 
if  a  dry  membrane  be  immersed  in  water,  it  absorbs  a  consider- 
able quantity,  recovers  its  softness  and  flexibility,  and  expands  in 
all  its  dimensions.  These  effects  are  greater  when  the  action  of 
warmth  is  combined  with  that  of  moisture,  A  membrane  will 
absorb  moisture  even  from  the  atmosphere,  and  again  part  with 
it,  according  to  its  different  states  of  humidity.  Philosophers 
have  availed  themselves  of  this  property  in  the  construction  of 
an  hygrometer,  or  instrument  for  indicating  these  varying  states 
of  the  atmosphere  with  respect  to  dryness  or  humidity.  Any 
long  slip  of  dried  membrane,  suspended  in  the  air,  and  stretched 

7 


74  MECHANICAL    TUNCTIONS. 

by  a  moderate  weight,  may  be  made  to  act  on  a  moveable  index 
by  any  mechanical  contrivance  rendering  the  variations  in  its 
length  visible  on  a  large  scale,  and  v\'ill  serve  the  purpose  of  an 
hygrometer.  The  menjbrane  will  be  found  to  lengthen  by  expo- 
sure to  a  humid  atmosphere,  from  which  it  imbibes  moisture,  and 
again  to  contract  by  the  evaporation  of  this  moisture  in  a  drier 
air. 

A  piece  of  catgut,  which  is  prepared  from  the  membrane  of  a 
sheep,  will  answer  the  same  purpose.  We  find,  accordingly, 
that  the  state  of  the  weather  has  a  considerable  effect  upon  the 
tone  of  a  musical  instrument  made  of  catgut.  A  violin,  or  harp, 
may  be  in  perfect  tune  in  one  situation,  and  yet  become  quite 
out  of  tune  when  placed  in  an  atmosphere  of  greater  humidity, 
as  in  that  of  a  room  filled  with  company. 

The  principle  of  which  these  facts  are  illustrations,  is  to  a 
certain  extent  applicable  to  the  animal  body.  The  doctrine  of 
the  animal  fibres  being  braced  or  relaxed,  which  was  formerly 
a  rtiore  fashionable  language  than  it  is  at  present,  may  perhaps 
have  been  carried  too  far,  but  it  has  certainly  a  foundation  in 
truth.  Warmth  and  moisture  have  a  powerful  influence  on  the 
body,  £fnd  their  efi'ect  is  partly  mechanical ;  and  this  operation, 
which  is  primarily  exerted  on  the  skin,  renders  them'  efficacious 
in  the  relief  of  inflammatory  action,  by  diminishing  the  tension  of 
the  inflamed  parts.  This  effect  is  not  merely  temporary,  but  may 
become  the  permanent  habit  of  the  system.  Thus,  we  find  that 
the  inhabitants  of  elevated  countries  where  the  air  is  peculiarly 
dry,  are  more  hardy,  and  possess  more  of  the  vis  tonica  in  their 
frames,  than  those  who  dwell  in  a  humid  climate,  or  in  low  and 
swampy  plains.  The  Swiss,  and  other  inhabitants  of  mountain- 
ous tracts,  may  in  this  respect  be  contrasted  with  the  Dutch  and 
Flemish,  who  have  in  general  a  constitutional  laxity  of  fibre;  and 
similar  differences  have  been  observed  in  the  lower  animals 
among  varieties  of  the  same  race. 

130.  All  these  properties  of  membrane,  taken  together,  adapt 
them  for  being  employed  in  various  useful  ways  in  the  animal 
economy.  Membranes  in  general  are  employed  to  establish  re- 
lations not  only  between  adjacent,  but  also  between  distant  parts ; 
they  strengthen  their  connexions,  and,  whilst  in  some  they  allow 
of  relative  motions  in  certain  directions,  and  to  a  certain  extent, 
in  others  they  restrain  them  and  limit  their  degrees.  Almost 
every  organ  is  furnished  with  a  firm  covering  of  membrane, 
which  gives  it  protection  and  support.  For  all  these  purposes, 
a  looser  and  more  yielding  cellular  tissue  would  not  have  posses- 
sed adequate  strength. 

131.  As  the  cellular  substance  is  the  basis  of  membrane,  so 
membrane,  in  different  modifications,  constitutes  the  essential 
portion  of  many  other  parts  of  the  body  ;   such  as  all  those  re- 


MEMBRANOUS  STRUCTURES.  75 

cipient  organs,  having  the  form  of  sacs  cr  pouches,  hke  the 
stomach,  and  especially  those  which  are  provided  for  the  retention 
of  fluids,  as  the  gall-bladder,  and  urinary  bladder.  Membranes 
are  also  formed  into  tubes  of  various  kinds,  destined  to  transmit 
their  fluid  contents  to  various  parts.  These  tubes,  known  under 
the  name  of  vessels,  canals,  or  duels,  are  also  frequently  furnished 
with  a  valvular  apparatus,  likewise  composed  of  membrane,  al- 
lowing of  the  passage  of  the  fluid  only  in  one  direction. 

132.' The  structure  and  properties  of  every  description  of 
membranes  have  been  minutely  investigated  by  Bichat,  who,  in 
his  Anatomie  Gin^rale,  has  given  us  an  elaborate  classification 
of  the  animal  textures.  He  establishes  two  general  divisions  of 
membranes,  namely,  the  simple  and  the  covrpound.  Of  the 
former  he  makes  three  classes;  first,  the  mucous  membranes,  the 
surface  of  which  is  defended  by  a  mucous  secretion  ;  secondly, 
the  serous  membranes,  characterised  by  the  serous  nature  of  the 
fluid  with  which  their  surface  is  constantly  moisiened;  and, 
thirdly,  the  fibrous  membranes,  which  are  distinguished  by  their 
peculiar  structure,  as  being  composed  of  dense  and  inelastic 
fibres.  The  compound  membranes  are  formed  by  the  intermixture 
of  two  or  more  of  the  simpler  membranes,  and  exhibit  a  combi- 
nation of  the  characters  of  each. 

133.  Serous,  membranes  are  universally  met  with  wherever 
there  are  internal  cavities  in  the  body,  which  are  closed  on 
every  side,  that  is,  have  no  communication,  by  any  channel, 
with  the  external  air;  such  cavities  being  always  lined  by  serous 
membranes.  This  is  exemplified  in  the  cavities  of  the  chest, 
which  are  three  in  number  ;  namely,  one  on  each  side,  containing 
the  right  and  left  lung,  and  the  intermediate  cavity,  occupied  by 
the  heart.  The  membranes  lining  the  former  are  called  the 
pleurcE ;  and  the  membrane  lining  the  latter,  the  pericardium. 
The  great  cavity  of  tha  abdomen,  in  which  are  situate  the  organs 
of  digestion  and  chylification,  is  lined  by  the  peritoneum,  which 
is  also  a  serous  membrane.  The  same,  also,  applies  to  the  cavites 
in  the  interior  of  the  brain,  which  are  called  ventricles,  and  also 
the  external  surface  of  the  organ,  which  are  lined  by  the  dura 
mater,  the  arachnoid  coat,  and  pia  mater.  The  serous  mem- 
branes, after  lining  their  respective  cavities,  are  extended  still 
farther,  by  being  reflected  back  upon  the  organs  inclosed  in  their 
cavities,  so  as  to  furnish  them  with  an  external  covering.  If  it 
were  possible,  therefore,  to  dissect  these  membranes  from  off"  the 
parts  which  they  invest,  they  would  have  the  form  of  a  sac 
without  an  opening,  the  organ  invested  by  one  of  their  folds, 
being  altogether  external  to  the  cavity  of  that  sac  ;  just  as  happens 
when  a  double  night-cap  is  worn,  of  which  the  part  immediately 
covering  the  head  is  analogous  to  that  portion  of  the  serous 
membrane  which  adheres  to,  and  invests  the  organ ;  whilst  the 


76  MECHANICAL    FUNCTIONS. 

external  portion  of  the  cap  represents  the  lining  of  the  cavity  in 
which  that  organ  is  said  to  be  contained. 

134.  Hence  it  will  readily  be  understood,  that  the  serous 
membranes  never  open,  or  allow  of  any  perforation,  for  the  pas- 
sage of  blood-vessels,  nerves,  or  ducts,  to  or  from  the  enclosed 
organs  ;*  but  that  they  are  always  reflected  over  those  parts, 
forming  a  sheath  round  them,  and  accompanying  them  in  their 
course.  It  also  follows,  as  a  necessary  consequence,  that  their 
free  surfaces  completely  isolate  the  parts  between  which  they 
intervene.  The  great  viscera,  suspended  in  the  bags  formed  by 
their  serous  coverings,  can  have  no  communication  with  the 
adjacent  parts,  except  ai  the  points  where  their  vessels  enter ;  in 
ali  other  situations  there  is  no  continuity  of  parts,  although  there 
may  be  contiguity. 

135.  In  every  serous  memjbrane  we  may  distinguish  two  sur- 
faces having  very  different  characters :  the  external  surface,  or 
that  by  which  they  adhere  to  the  surrounding  organs,  and  the 
internal  surface,  which  is  in  immediate  contact  with  another 
portion  of  the  same  membrane,  but  without  adhering  to  it.  This 
interior  surface  is  remarkable  for  its  perfect  smoothness  and 
polish ;  and  it  is  continually  preserved  in  a  state  of  moisture  by 
a  serous  fluid,  which  exudes  from  it.f  This  fluid  has  been 
termed  the  liquid  of  surfaces,  and  consists  almost  entirely  of 
water,  with  a  very  minute  proportion  of  albuminous  matter.  Its 
presence  is  evidently  of  the  greatest  use  in  facilitating  the  mo- 
tions of  the  parts  contained  within  the  cavities,  with  relation  to 
their  sides,  by  diminishing  friction,  preserving  the  smoothness  of 
the  surfaces  applied  to  each  other,  and  preventing  their  mutual 
adhesion.  When  the  internal  surface  of  these  membranes  is 
exposed  to  the  air  in  living  animals,  or  immediately  after  death, 
this  fluid  exhales  in  the  form  of  vapour,  to  which  formerly  great 
attention  was  paid,  and  which  was  dignified  with  the  name  of 
halitus.  In  consequence  of  disease,  this  fluid  of  surfaces  some- 
times accumulates  in  one  of  these  cavities,  and  thereby  produces 
a  dropsy  of  that  respective  cavity :  a  fact  which  proves  the 
pov/er  of  serous  membranes  to  retain  these  fluids,  and  not,  as 
in  the  case  of  the  cellular  substance,  to  allow  of  their  diffusion 
into  the  adjoining  organs. 

136.  The  serous  membranes  constitute  the  simplest  form  of 
condensed   cellular  substance ;  they  are  not  divisible  into  any 

*  [The  only  exception  to  this  is  in  the  case  of  the  peritoneuna,  on  which 
the  ventral  extremities  of  the  fallopian  tubes  terminate.] 

f  [Rudolphi  (^Grundriss  der  Fhysiologie,  113)  asserts,  that  some  membranes 
are  incapable  of  inflammation,  are  not  vascular,  and  do  not  secrete,  buttliatthe 
secretions  of  shut  sacs  take  place  from  the  subjacent  parts  and  transude  the 
serous  membranes  proper,  which,  in  his  view,  are,  consequently,  a  kind  of 
epidermis.] 


OSSEOUS    FABRIC.  77 

regular  layers ;  although  cellular  portions  may  be  removed  from 
the  outer  surface  by  which  they  are  attached  to  the  surrounding 
parts.  In  the  natural  state  they  are  exceedingly  thin  and  trans- 
parent; but  become  thicker  and  opaque  by  disease.  Although 
perfectly  flexible,  they  possess  considerable  strength ;  they  are 
exceedingly  extensible ;  but  they  are  not  in  the  same  proportion 
elastic  :  for  after  they  have  been  stretched,  they  give  but  feeble 
indications  of  a  power  of  retraction. 

4.   The  Osseous  Fabric. 

137.  For  the  purpose  of  thoroughly  understanding  the  whole 
mechanism  and  operations  of  any  complicated  engine,  or  system 
of  machinery,  the  best  and  most  natural  course  is  to  commence- 
with  the  study  of  the  solid  framework,  which  gives  stability  to 
the  whole  fabric,  and  affords  fixed  bearings  from  which  the 
powers,  regulating  the  movements  of  its  different  parts,  exert 
their  respective  powers.  This  purpose  of  procuring  mechanical 
rigidity  and  support,  is  the  appropriate  function  of  the  osseous 
system,  or  skeleton  ;  which  is  composed  of  a  connected  series  of 
solid  structures,  called  hones,  deriving  their  mechanical  proper- 
ties from  their  peculiar  chemical  composition,  and  almost  crys- 
talline hardness,  and  which  constitute  one  of  the  most  important 
of  the  constituent  textures  of  the  body.  Our  first  object  of  atten- 
tion, therefore,  in  considering  the  mechanical  functions,  is  the 
study  of  this  system  of  structures. 

138.  The  bones,  then,  are  to  be  viewed  as  the  densest  and 
most  solid  parts  of  the  animal  frame;  constituting  the  basis  of 
support  to  the  softer  textures,  affording  protection  to  all  the  vital 
organs,  and  furnishing  those  powerful  levers  which  are  essential 
to  the  advantageous  action  of  the  muscles  concerned  in  locomo- 
tion, and  in  the  various  movements  of  the  limbs.  With  reference 
to  their  form,  they  have  usually  been  divided  into  three  classes : 
\he  long  cylindrical  hones;  the  broad  and  fat  bones;  and  the 
sho7^t  or  square  bones,  which  include  those  of  a  more  irregular 
form,  and  not  referable  to  either  of  the  other  two  heads.  To 
the  first  class  belong  the  principal  bones  of  the  upper  and  lower 
limbs,  which  are  adapted  more  especially  to  the  purposes  of 
motion.  Under  the  second  may  be  ranked  the  bones  of  the  skull, 
which  serve  for  the  protection  of  the  brain  ;  and  the  third  include 
the  vertebras,  the  bones  of  the  face^  and  the  small  bones  which 
concur  in  the  formation  of  the  wrist  and  the  ankle.  There  are, 
besides,  other  bones,  such  as  the  ^ibs  and  the  bones  of  the  pelvis, 
of  a  more  anomalous  description,  which  are  rather  distinguished 
by  their  irregularity  than  by  any  definite  character. 

139.  On  examining  the  mechanical  structure  of  bones,  we 
find  that  their  external  surface  is  generally  their  hardest  part, 

7* 


78  MECHANICAL    FUNCTIONS. 

and  that  it  consists  of  a  solid  plate,  or  layer  of  bony  matter,  of 
different  thickness  in  different  bones,  and  in  different  parts  of  the 
same  bone.  In  the  cylindrical  bones  this  firm  and  compact  sub- 
stance extends  only  to  a  certain  depth,  and  within  this  the  struc- 
ture is  spongy  and  cellular.  To  the  latter  part  the  name  cancelli 
has  been  given.  In  the  middle  of  the  long  bones  the  central 
parts  are  occupied  by  the  marrow  ;  but  as  we  continue  our 
examination,  by  taking  different  sections  across  the  bone, 
in  proportion  as  we  approach  the  extremities,  we  find  the 
dense  external  substance  diminishing  in  thickness,  while  the 
proportion  of  the  spongy  part  increases,  and  encroaches  upon 
the  space  in  the  centre  occupied  by  the  marrow,  which  at 
length  disappears,  so  that  at  the  very  extremity  of  the  bone, 
nearly  the  whole  area  of  the  section  is  filled  by  the  cancelli, 
while  the  outer  covering  of  solid  bone  is  merely  a  thin  superficial 
plate.  In  the  ffat  bones,  having,  of  course,  an  upper  and  under 
surface,  the  plates  of  bone  forming  each  of  these  surfaces,  are 
termed  the  two  tables,  and  the  cellular  portion  which  is  found 
between  them  is  called  the  diploe.  In  many  of  the  more  irregu- 
larly shaped  bones,  neither  cancelli  nor  diploe  are  found,  the  whole 
substance  being  compact.  Dr.  Bostock  observes,  that  the  transi- 
tion from  the  compact  to  the  spongy  part  of  a  bone  is  not  marked 
by  any  decided  limit ;  but  they  pass  into  each  other  by  insensible 
degrees,  so  as  to  show  that  there  is  no  essential  difference  between 
them.* 

140?  Bones  present  the  appearance  of  fibres  on  their  surface. 
This  is  seen  particularly  in  all  bones  that  have  been  long 
exposed  to  the  weather,  or  that  have  been  long  boiled.  In  the 
cylindrical  bones  most  of  these  fibres  are  longitudinal ;  but  in  the 
flat  bones  they  generally  run  in  a  radiated  direction.  In  the 
short  bones  their  course  is  much  more  iiTegular  and  diflficult  to 
trace.  In  the  compact  part  of  the  section  oi  a  bone,  the  appear- 
ance of  plates  is  not  very  distinguishable  ;  but  certain  cavities 
are  discovered  which,  for  the  most  part,  run  in  a  longitudinal 
direction,  and  nearly  parallel  to  one  another.  They  are  of 
various  lengths ;  and  their  diameters  are  exceedingly  small. 
They  have  transverse  or  oblique  canals,  which  establish  communi- 
cations between  them ;  and  some  of  which  also  open  into  the  larger 
cancelli  in  the  middle  of  the  bone.  These  cavities  have  been 
called  the  canals  of  Havers,f  who  first  discovered  them.  Their 
existence,  however,  was  for  a  long  time  considered  dubious  ;  but 
it  has  been  lately  verified  by  Mr.  Howship,J  who,  with  the  help 
of  the  solar  microscope,  oblaiijed  distinct  views  of  them,  and  was 

*  Elementary  System  of  Physiology,  third  editicn,  p.  61. 

f  Osleologia  nova,  §35,  37. 

X  Medico-Chirurgical  Transactions,  vii,  393. 


OSSEOUS    FABRIC.  79 

enabled  to  trace  their  course.  He  ascertained  the  diameter  of 
these  canals  to  be  about  the  400th  of  an  inch;  and  farther  disco- 
vered that  they  are  lined  with  an  extremely  fine  vascular  mem- 
brane, and  that  they  are  filled  with  marrow. 

141.  The  intimate  structure  of  bone  was  first  minutely  investi- 
gated by  Malpighi,  who  discovered  that  its  basis  consists  of  an 
animal  membrane  having  an  areolated,  or  cellular  form.  Duha- 
mel*  next  ascertained  that  this  membranous  matter  was  fre- 
quently disposed  in  plates  or  laminae  ;  and  he  described  these 
plates  as  forming  concentric  rings,  analogous  to  those  which 
compose  the  trunk  of  a  tree ;  but  there  is  no  other  foundation 
than  mere  fancy  for  this  analogy.  We  owe  to  Herissantf  the 
important  fact,  that  the  chief  properties  of  bone  are  derived  from 
the  presence  of  an  earthy  ingredient,  which  is  deposited  in  the 
animal  basis,  or  parenchyma  of  the  bone. 

142.  The  analysis  of  a  bone  into  its  two  constituent  parts  is  easily 
effected  by  the  agency  either  of  acids  or  of  heat.  By  macera- 
ting a  full-grown  bone  for  a  sufficient  time  in  diluted  muriatic 
acid,  the  earthy  portion  of  the  bone,  amounting  to  nearly  one- 
third  of  its  weight,  is  dissolved  by  the  acid  ;  the  animal  portion 
only  remaining.  This  animal  basis  retains  the  bulk  and  shape 
of  the  original  bone,  but  is  soft,  flexible,  and  elastic;  possessing, 
in  a  word,  all  the  properties  of  membranous  parts,  and  corres- 
ponding in  its  chemical  charaoSer  to  condensed  albumen.J  A 
•portion  of  this  solid  animal  substance  affords  gelatin  by  long 
boiling  in  water,  especially  under  the  pressure,  admitting  of  a 
high  temperature,  to  which  it  may  be  subjected  in  Papin's  digester. 
On  the  other  hand,  by  subjecting  a  bone  to  the  action  of  fire,  the 
animal  part  alone  will  be  consumed,  and  the  earth  left  untouched, 
preserving,  as  before,  the  form  of  the  bone,  but  having  lost  the  ma- 
terial which  united  the  particles,  presenting  a  fragile  mass  which 
easily  crumbles  into  powder.  This  earthy  basis,  when  chemi- 
cally examined,  is  found  to  consist  principally  of  phosphate  of 
lime,  which  composes  eighty-two  hundredths  of  its  weight ;  and 
to  contain  also,  according  to  Berzelius,  minute  portions  of  fluate 
and  carbonate  of  lime,  togethei:  with  the  phosphates  of  magnesia 
and  of  soda. 

Dr.  G.  O.  Rees,  who  has  lately  made  exact  analyses  of  different 
hones  taken  from  the  same  individual,  in  a  state  of  perfect  dry- 
ness, and  quite  free  from  fat,  periosteum,  or  cartilages,  deduces 
from  his  researches  the  following  conclusions  :§  1.  The  long 
bones  of  the  extremities  contain  more  earthy  m.atter  than  those 
of  the  trunk.     2.  The   bones    of   the   upper  extremity  contain 

*  Memoires  de  TAcademie  des  Sciences,  pour  1739,  17-11,  1742-,  and  1743. 
flbid.  1758. 

:j:  This  was  first  satisfactorily  shown  by  Mr.  Ilatchelt.   Phil.  Trans,  for  1800. 
§  Medico-Chirurgical  Transactions,  xxi.  409. 


80  MECHANICAL    FUNCTIONS. 

somewhat  more  earthy  matter  than  the  corresponding  bones  of 
the  lower  extremity  ;  thus  the  humerus  more  than  Jthe  femur,  and 
the  radius  and  ulna  more  than  the  tibia  and  fibula;  this  difference  is, 
however,  small,  being  about  one-half  per  cent.  3.  The  humerus 
contains  more  earthy  matter  than  the  radius  and  ulna,  and  the  femur 
.more  than  the  tibia  and  fibula.  4.  The  tibia  and  fibula  contain,, 
as  nearly  as  possible,  the  same  proportions  of  animal  and  earthy 
matter,  and  the  radius  and  ulna  may  also  be  considered  alike  in 
constitution.  5.  The  vertebrae,  ribs,  and  clavicle,  are  nearly 
identical  as  regards  the  proportion  of  earthy  matter;  the  ileum 
contains  somewhat  more  of  the  earth,  the  scapula  and  sternum 
somewhat  less ;  the  sternum  contains  more  earthy  matter  than 
the  gcapula.  6.  The  bones  of  the  head  cqntain  considerably 
more  earthy  matter  than  the  bones  of  the  trunk,  as  observed  by 
Dr.  J.  Davy  ;  but  the  humerus  and  other  long  bones  are  very 
nearly  as  rich  in  earths.  7.  The  metatarsal  bones  may  probably 
be  ranked  with  those  of  the  trunk  in  proportional  constitution. 
8.  The  cancellated  structure  (at  least  in  the  rib)  contains  less 
earthy  matter  than  the  more  solid  parts  of  the  bone ;  this  dif- 
ference, however,  is  not  considerable.  9.  The  bones  of  the  trunk 
of  the  foetal  skeleton  are  as  rich  in  the  proportion  of  earthy  matter 
as  those  of  the  adults ;  at  least  the  difference  is  too  small  to  be 
material.  10.  The  bones  of  the  foetal  extremities,  on  the  other 
hand,  are  deficient  in  earthy  matter,  which  is  a  fact  simply  ex- 
plicable from  the  circumstance  that  such  an  excess  of  earths  as 
appears  necessary  to  very  great  strength  of  bone  is  not  needed 
at  birth,  and  therefore  only  appears  in  after  life.* 

The  existence  of  a  general  law,  regulating  the  proportion  of 
earthy  deposit  in  the  different  bones,  (which  is  shown  by  the 
curious  agreement  of  relative  proportions  observed  between  the 
foetal  and  adult  skeletons,)  adds  one  more  to  the  many  proofs  of 

*  [Professor  Miescher,  of  Basel,  in  Switzerland,  who  has  published  an  excel- 
'lent  account  of  the  general  anatomy  of  bones,  with  which  he  has  favoured  the 
Editor,  gives  the  following  as  the  proportions  of  the  animal  and  earthy  parts. 

Infants.  Adults.  Aged. 

Animal  matter,      .         .         .         47.20  20.18  12.20 

Earthy  matter,      .         .         .         48.48  74.84  84.10 


95.68  95.02  96.30 

The  proportions,  however,  differ  in  the  different  bones  :  According  to  Thilenius, 
in  a  dissertation  on  the  chemical  composition  of  bones,  published  at  Got- 
tingen,  in  1823,  the  bones  of  the  extremities  of  the  new-born  infant,  freed 
from  animal  matter  by  burning,  left  57.59  per  cent.  ;  the  vertebra  of  the  neck 
and  back,  47.41  ;  the  clavicle  of  a  boy,  63.26;  the  os  frontis  and  os  parietale, 
65.21;  the  petrous  bone  of  the  adult,  68.72;  the  bones  of  the  extremities, 
66.66;  the  ribs,  63.37;  the  frontal,  femoral,  occipital,  and  inferior  maxillary 
bone  of  an  old  person,  66.79. — Miescher,  De  Injlammatione  Ossium  eorumque 
Anatome  Generali,  p.  48  :  Berol.  1836.  See,  also,  Pancousfs  Edition  of  Wis- 
tar's  Anatomy^  i.  29.     Phil  ad.  1838.] 


OSSEOUS    FABRIC.  81 

the  regularity  and  perfection  of  design  wiiich  nature  evinces  in 
her  operations. 

143.  It  appears  evident,  then,  from  these  and  other  facts,  that 
the  basis  of  the  osseous  structure  is  essentially  the  same  as  that 
of  membranous  parts,  being  composed  of  fibrous  laminae  or  plates, 
which  are  connected  together  so  as  to  form,  by  their  intersection, 
a  series  of  cells  analogous  to  those  of  the  cellular  texture.  In 
the  interstices  of  these  plates,  or  in  the  cells  themselves,  the  par- 
ticles of  phosphate  of  lime  are  deposited  ;  the  particles  being  held 
in  union  by  the  interposed  membrane,  which  performs  the  office 
of  a  cement.  Hence  there  is  no  necessity  for  admitting  the 
hypothetical  explanation  of  Gagliardi,*  who  maintained,  that  the 
bony  plates  are  held  together  by  small  processes,  like  nails,  which, 
rising  from  the  inner  plates,  pierce  through  the  adjoining  ones,  and 
are  fixed  into  the  more  external  plates.  Of  these  processes,  or 
claviculi,as  he  called  them,  he  described  four  different  kinds,  the 
perpendicular,  the  oblique,  the  headed,  and  the  crooked.  But 
no  subsequent  anatomist  has  been  able  to  verify  these  observa- 
tions ;  and  the  account  given  by  Gagliardi  remains  on  record  as 
a  curious  instance  of  the  extent  to  which  an  observer  of  mere 
appearances  is  liable  to  deceive  himself  by  the  influence  of  too 
vivid  an  imagination.  Monro^  states,  that  in  bones  fitly  prepared 
he  could  only  see  numerous  irregular  processes  rising  out  from 
the  plates.  .  Duhamel,  trusting  to  a  fancied  analogy  between  the 
process  of  ossification,  and  the  growth  of  trees,  imagined  that  a 
bone  is  composed  of  a  series  of  regular  concentric  laminae.  But 
this  hypothesis  has  been  refuted  by  Scarpa,f  who  investigated, 
with  great  care,  both  the  mechanical  structure  of  bone  and  the 
mode  of  its  formation ;  and  concludes  that  the  ultimate  texture 
of  bone  is  not  lamellated  but  reticular.  Raspail  has  indulged  in 
speculations  of  a  still  more  questionable  nature  respecting  the 
ultimate  osseous  texture,  which  he  endeavours  to  assimilate  with 
that  vesicular  form,  which  he  views  as  the  essential  character 
both  of  animal  and  of  vegetable  organization.  Dr.  Benson 
observesj  that  all  writers,  before  the  time  of  Scarpa,  considered 
the  structure  of  bone  as  laminated,  or  fibrous  and  laminated; 
whilst,  according  to  all  later  authorities,  it  should  be  regarded  as 
cellular.  In  the  works  of  the  former,  however,  we  may  notice 
intimations  of  a  reticular  texture ;  and  in  those  of  the  latter,  on 
the  other  hand,  we  meet  with  the  expressions  of  a  tendency  or 
disposition  to  a  laminated  arrangement.  '•  If,  with  these  opinions 
before  us,"  he  continues,  "  we  come  to  examine  for  ourselves, 
we  shall  have  no  hesitionin  agreeing  with  Scarpa  that  it  is  really 
cellular.     At  the  same  time,  it  must  be  confessed >  that  the  sides 

*  Anatomia  Ossium.  f  De  Penit.  Structura  Ossium. 

X  Cyclopaedia  of  Anatomy  and  Physiology,  vol.  i.  p.  433. 


82  MECHANICAL    FUNCTIONS. 

of  the  cells  are,  in  the  compact  tissue,  so  pressed  together,  that 
the  appearance  of  laminas  is  often  very  striking;  and,  again,  that 
the  sides  of  the  cells  have,  in  most  places,  the  appearance  of 
fibres;  whep  the  earthy  portion  is  removed  by  an  acid,  we  can 
tear  out  with  a  pin  the  membranous  fibres,  and  almost  demonstrate 
the  fibres.  But  a  closer  examination  will  show  that  we  have 
torn  the  cells,  and  destroyed  the  true  texture.  The  laminated 
disposition  supposed  to  be  shown  by  exfoliation,  the  weather, 
burnino-,  &c.,  may  all  be  proved  to  be  deception ;  and  there  can 
seldom,  indeed,  be  exhibited  a  plate,  however  small,  of  equal 
thic4cness  throughout,  which  has  been  removed  by  any  of  these 
agents.  There  is,  however,  an  approach  to  the  laminated  ar- 
rangement, and  every  cell  is  formed  of  particles  which  approach 
to  the  form  of  fibres.  The  longitudinal  canals  of  Havers,  Leu- 
w^enhoeck,  and  Howship,  probably  result  from  the  flattened  cells, 
and  may  be  deceptive  appearances  in  the  old  bone,  or  the  chan- 
nels for  blood-vessels,  &c." 

144.  Bones  are  invested  on  every  part  of  their  surface,  ex- 
cepting in  those  parts  where  they  are  plated  with  cartilage,  with 
a  firm  plate  of  membrane,  termed  the  periosteum,  which  conveys 
blood-vessels  to  the  bone,  and  establishes  mechanical  connexions 
between  it  and  surrounding  parts.  This  membrane  belongs  to 
the  class  of  fibrous  textures,  being  composed  of  numerous  in- 
elastic fibres  of  great  density  and  strength,  passing  in  various 
directions,  and  composing  a  kind  of  ligamentous  tissue,  interlacing 
with  the  fibres  of  the  ligaments  which  encircle  the  joints. 

The  inner  surface  of  the  periosteum  is  connected  with  the  bone 
by  the  vessels  passing  from  the  one  to  the  other,  and  also  by 
numerous  prolongations  which  dip  down  into  the  osseous  sub- 
stance. The  blood-vessels  of  this  membrane  are  numerous.,  and 
easily  rendered  apparent  by  means  of  injections,  especially  in 
young  subjects.  Besides  the  more  obvious  uses  of  the  periosteum, 
in  affording  protection  to  the  surface  of  bones  from  injurious 
impressions,  which  they  might  receive  from  the  action  of  sur- 
rounding parts,  and  interposing  a  membranous  layer  for  the 
defence  of  the  latter,  Bichat  ascribes  to  it  the  more  important 
ofiice  of  affording  fixed  centres  of  support  to  the  general  system 
of  fibres,  in  its  mechanical  relations  to  the  rest  of  the  frame. 
The  periosteum  which  covers  the  bones  of  the  skull  has  received 
the  name  of  the  pericranium. 

145.  The  internal  cavities  of  the  bones  are,  as  is  well  known, 
occupied  by  an  oily  secretion,  termed  the  marroiv,  contained  in 
a  delicate  structure,  composed  of  minute  vesicles  which  are  filled 
with  the  fluid  oil,  and  which  are  connected  by  fine  threads  and 
plates  of  fine  cellular  tissue.  Monro  describes  the  vesicles  as  per- 
fectly distinct,  having  no  communication  with  one  another,  and 


CARTILAGE.  83 

as  presenting,  under  the  microscope,  the  appearance  of  a  cluster 
of  pearls. 

Many  have  been  the  conjectural  uses  assigned  to  the  marrow 
by  the  older  physiologists  ;  it  was  at  one  time  very  generally 
imagined  that  it  served,  by  its  mechanical  properties,  to  temper 
the  brittle  quality  of  the  earthy  materials  which  form  the  chief 
constituent  portion  of  the  bone  ;  a  purpose,  however,  which  it  is 
impossible  it  could  fulfil,  as,  instead  of  being  mixed  up  and  blended 
with  the  phosphate  of  lime,  or  diffused  generally  through  the 
substratum  of  the  bone,  it  is  lodged  in  separate  cavities,  and 
thereby  prevented  from  any  union  with  bony  matter,  or  inter- 
mixture with  its  substance.  The  marrow  is,  in  general,  possessed 
of  little  sensibility,  except  in  a  few  points,  where  it  is  traversed 
by  the  nervous  filaments  supplying  the  bone  itself.  It  is  regarded 
by  physiologists  of  the  present  day  rather  as  constituting  a  part 
of  the  general  store  of  nutritious  matter,  which  is  kept  in  re- 
serve for  particular  occasions  of  exigency,  than  as  having  any 
mechanical  relation  with  the  dense  texture  within  which  it  is 
lodged.  The  circumstance  of  its  being  wholly  absent  in  the 
bones  of  birds  is  a  clear  proof  that  there  is  no  mutual  dependence 
between  the  functions  of  the  latter  and  the  presence  of  the  marrow. 

146.  All  the  internal  cavities  of  bones  occupied  by  the  marrow 
are  lined  with  a  vascular  membrane,  which  follows  all  the 
windings  of  the  canals  and  of  the  cancelli,  and  has  been  called 
the  internal  periosteum.  It  may  easily  be  rendered  visible  by 
sawing  a  long  bone  longitudinally,  and  plunging  it '  in  boiling 
water,  by  which  treatment  the  membrane  is  made  to  detach 
itself  from  the  bone,  and  contract  upon  the  marrow  which  is 
within  it,  and  to  which  it  is  closely  attached.  It  has  then  the 
appearance  of  a  fine  cobweb. 

5.   Cartilage. 

147.  The  structure  which  ranks  next  to  bone  in  respect  to  its 
density  is  cartilage,  a  term  which  expresses  a  firm  and  dense  sub- 
stance, apparently  homogeneous  in  its  texture,  semipellucid,  and 
of  a  milk-white  or  pearly  colour.  Substances  of  this  description 
are  found  to  enter  into  the  composition  of  several  parts  of  the 
body.  The  surface  of  a  cartilage  is  perfectly  uniform,  and  pre- 
sents no  visible  eminences  or  pores ;  nor  can  any  cavities  or 
inequalities  of  any  kind  be  perceived  in  its  internal  texture.  When 
it  is  cut  into  with  a  sharp  knife,  the  section  exhibits  a  uniform 
appearance,  like  that  of  a  piece  of  glue.  Yet,  after  exposure  for 
a  certain  time,  the  surface  thus  cut  begins  to  contract,  and  a 
serous  fluid  is  perceived  slowly  to  exude  from  it,  proceeding 
from  certain  invisible  pores,  which  are  in  all  probability  minute 
capillary  vessels,  of  which  the  diameters  are  too  small  to  admit 


84  MECHANICAL    FUNCTIONS. 

the  coloured  globules  of  the  blood.  That  a  delicate  system  of 
circulating  passages  exist  in  cartilages,  is  shown  by  various  dis- 
eased conditions,  in  which  sometimes  granulations  have  been  seen 
to  arise  from  their  surfaces,  and  at  other  times  extensive  absorp- 
tion of  their  substance  has  taken  place  ;  and  although  insensible, 
on  ordinary  occasions,  to  wounds  inflicted  by  cutting  instruments, 
yet  in  others,  when  sudden  pressure  is  made  on  them  under  pe- 
culiar circumstances,  extreme  pain  arises,  giving  warning  of 
serious  injury  impending. 

Cartilaginous  structures  appear  to  be  composed  of  albumen 
alone,  with  scarcely  any  intermixture"  of  gelatin.  Dr.  John  Davy 
found  that  they  contain  a  small  proportion  of  phosphate  of  lime, 
amounting  to  about  the  two  hundredth  part  of  their  weight. 
Mr.  Hatchett,  however,  does  not  regard  the  substance  as  an 
essential,  ingredient  in  their  composition. 

The  mechanical  property  which  particularly  dintinguishes 
cartilage  is  elasticity,  a  quality  which  it  possesses  in  a  greater 
degree  than  any  other  animal  structure,  and  which  adapts  it  to 
many  useful  purposes  in  the  economy.  Hence  it  forms  the  basis 
of  many  parts  where,  contrary  to  the  purposes  answered  by  the 
bones,  phancy  and  resilience  as  well  as  firmness  are  required ; 
and  hence  cartilage  is  employed  when  a  certain  shape  is  to  be 
preserved,  together  with  a  capability  of  yielding  to  an  external 
force.  The  flexibility  of  cartilage,  however,  does  not  extend 
beyond  certain  limits ;  if  these  be  exceeded,  fracture  takes  place. 
Great  density  bestowed  upon  an  animal  structure,  indeed,  appears 
to  be  in  all  cases  attended  with  a  proportionate  degree  of  brittle- 
ness.  These  mechanical  properties  of  cartilages,  as  well  as  their 
intimate  structure,  although  nearly  homogeneous  in  all,  are 
subject  to  modification  in  different  kinds  of  cartilage.  Cartilages 
are  covered  with  a  fine  membrane,  termed  the  perichondrium, 
analogous  in  its  structure  and  office  to  the  periosteum,  which  we 
have  already  had  occasion  to  point  out  among  the  fibrous  mem- 
branes, as  investing  the  bones. 

148.  Cartilages  are  distinguished  into  those  which  are  tempo- 
rary and  those  which  are  permanent  structures.  The  former 
are  only  met  with  in  the  earlier  periods  of  life,  during  the  growth 
of  the  body,  and  are  gradually  removed  to  make  way  for  the 
deposition  of  bone.  When  about  to  undergo  this  change,  small 
canals  have  been  detected  in  the  substance  of  these  temporary 
cartilages.  The  permanent  cartilages  are  those  which  retain  the 
cartilaginous  structure  throughout  every  period  of  life.  They 
have  been  distinguished  into  three  or  four  different  kinds,  such 
as  the  membraniform,  the  interosseal,  the  articular,  and  the 
interarticular  cartilages. 

149.  The  membraniform  cartilages  are  included  by  Bichat  in 
the  class  of  fibro-cartilaginous  structures  hereafter  to  be  de- 


CARTILAGE.  86 

scribed.  They  furnish  a  basis  of  support  to  the  softer  parts,  and 
in  some  measure  supply  the  place  of  bone,  giving  a  determinate 
shape  and  firmness  to  parts  where  bone  would  have  been  incon- 
venient. They  possess  greater  tenacity  and  less  brittleness  than 
the  other  kinds  of  cartilage.  By  their  elasticity  they  admit  of 
considerable  variation  of  figure,  yielding  to  external  pressure, 
and  recovering  their  proper  shape  as  soon  as  the  pressure  is 
removed.  Of  this  kind  are  the  cartilages  of  the  nose  and  ear, 
and  also  those  of  the  larynx  and  trachea.  These  cartilages  are 
extremely  thin,  and  are  invested  with  a  very  thick  and  firm  peri- 
chondrium, to  which  they  are  connected  by  means  of  a  number 
of  fibres  traversing  their  substance,  and  rendering  their  sarfaces 
rough  and  porous.  Long  maceration  enables  us  to  detect  these 
fibres,  and  to  resolve  the  whole  into  a  cellular  and  albuminous 
substance. 

150.  The  interosseal  cartilages  pass  from  one  bone  to  another, 
adhering  firmly  by  their  extremities  to  each.  They  answer  the 
same  purpose  as  would  be  attained  by  an  increase  of  extent  in 
one  or  both  of  the  bones,  with  the  further  advantage  of  allowing 
of  obscure  degrees  of  motion,  and  deadening  the  eflJects  of  jars 
incident  to  percussion.  The  cartilages  of  the  ribs  are  of  this 
class.  They  are  covered  with  perichondrium.  When  they  have 
been  steeped  in  water  for  a  great  many  months,  they  are  divisi- 
ble into  laminas,  of  an  oval  shape,  which  are  united  by  fibres 
passing  obliquely  between  them. 

151.  The  articular,  or  diarthrotlial  cartilages,  are  those 
plates  of  cartilaginous  substance  which  adhere  firmly,  and  almost 
inseparably,  to  the  surfaces  of  those  bones  which  are  opposed  to 
each  other  in  the  joints,  or  over  which  tendons  and  ligaments 
slide.  In  some  joints  the  whole  of  the  surface  of  the  bone  within 
the  capsular  ligament  is  covered  with  cartilage ;  in  others,  only 
the  parts  of  bones  which  move  upon  each  other ;  the  remaining 
part  being  covered  with  ligament.  This  latter  disposition  is 
met  with  in  the  joint  of  the  hip.  This  kind  of  cartilage,  like  the 
others,  appears  perfectly  smooth  on  its  surface,  and  also  w^hen  a 
section  is  made  through  its  substance ;  but  by  a  sufficiently  long 
maceration,  to  allow  of  a  commencement  of  putrefaction,  its 
fibrous  structure  may  be  detected.  The  elastic  resilience  of  these 
cartilages  has  a  powerful  tendency  to  lessen  the  shocks  incident 
to  sudden  and  violent  actions. 

152.  Cartilages  of  a  similar  kind  are  found  in  the  cavities  of 
certain  joints,  and  have  hence  been  called  inter  articular  carti- 
lages. They  have  no  immediate  connexion  with  the  bones 
forming  the  joint,  but  are  attached  only  to  the  inside  of  the 
capsular  ligament.  They  are  thus  rendered  somewhat  moveable, 
and  being  interposed  between  the  bones,  allow  them  a  greater 
latitude  of  motion,  while  they  at  the  same  time  contribute  to 


86  MECHANICAL    FUNCTIONS. 

adapt  their  surfaces  more  perfectly  to  each  other.  By  long 
maceration  in  water,  a  laminated  structure  is  more  distinctly 
perceived  in  this  kind  of  cartilage  than  in  any  of  others. 

6.  Fibro-Cartilaginous  Structures. 

153.  Many  structures  exist  in  the  human  body  which  appear 
to  be  of  an  intermediate  nature  between  ligament  and  cartilage, 
in  which  a  fibrous  texture  is  united  to  a  cartilaginous  basis,  and 
which  combine  the  characteristic  properties  of  both  these  tex- 
tures. They  are  distinguished  from  the  purely  ligamentous  parts 
by  their  high  degree  of  elasticity,  and  fronri  cartilage  by  their 
fibrous  texture.  Accordingly  we  find  them  employed  when  this 
combination  of  properties  is  requisite  for  the  functions  of  the 
parts.  They  form  additions  to  interarticular  ligaments,  and  eke 
out  the  borders  of  cavities  adapted  to  the  reception  of  the  rounded 
heads  of  bones. 

154.  The  principal  instances  of  large  masses  of  fibro-cartila- 
ginous  structures  occur  in  those  which  unite  the  bodies  of  the 
vertebree  and  of  the  bones  of  the  pelvis.  These  intervertebral 
substances,  as  they  are  termed,  impart  great  elasticity  to  the 
spine;  and  diminish  the  effects  of  concussion.  When  the  body 
has  been  long  ni  the  erect  position,  the  weight  of  the  head  and 
upper  parts  of  the  trunk  occasions  the  compressionof  these  inter- 
vertebral substances,  and  the  height  of  the  person  is  diminished. 
By  continuance  for  an  equal  time  in  a  horizontal  posture,  this 
super-incumbent  pressure  being  removed,  they  recover  their  ori- 
ginal dimensions.  Hence  a  person  is  taller  when  he  rises  in  a 
morning  than  after  sustaining  the  fatigues  of  the  day ;  and  the 
difference  of  stature  often  amounts  to  a  whole  inch.* 

7.  Ligamentous  Structures. 

155.  Structures  possessing  inferior  degrees  of  soHdity,  but  still 
exhibiting  considerable  density,  are  met  with  in  the  interior  of 
the  body,  and  serve  various  mechanical  purposes  of  cohesion 
and  support.  Many  of  these  may  be  regarded  as  mere  modifi- 
cations of  membrane ;  but  yet  the  peculiarities  of  structure  and 
of  properties,  exhibited  by  ligamentous  textures,  point  them  out 
as  requiring  to  be  classed  separately.  Bichat,  who  has  viewed 
them  as  composing  a  system  of  structures,  has  given  to  it  the 
title  of  the  fibrous  system  ;  a  name  which  is  Hable  to  the  objection 
of  not  being  sufficiently  distinctive  ;  since,  as  we  shall  afterwards 
find,  many  other  parts,  and  especially  the  muscles,  are  no  less 

*  [Buffon  asserts,  that  the  son  of  one  of  his  most  zealous  collaborafeurs, 
M.  Gueneau  de  Montbeillard,  a  young  man  of  tail  stature,  lost  an  inch  and  a 
half,  after  having  danced  all  night.] 


LIGAMENTOUS  STUUCTURES.  87 

fibrous  than  the  tendons  and  the  ligaments.  As  a  general  desig- 
nation of  this  class  of  fibres,  we  liave  therefore  preferred  the  term 
of  ligamentous  system,  which  sufficiently  expresses  the  general 
mechanical  purpose  which  they  are  designed  to  serve  in  the  ani- 
mal economy. 

156.  This  system  includes  a  great  number  of  structures,  which, 
although  very  similar  in  their  nature  and  office,  have  received 
different  names,  such  as  ligaments,  tendons,  fascice,  aponeuroses, 
capsules,  &c.  Fibres  of  a  similar  kind  to  those  which  constitute 
these  parts,  also  enter  into  the  composition  of  other  organs, 
imparting  to  them  different  degrees  of  mechanical  strength. 

157.  Various  as  are  the  forms  and  dispositions  assumed  by  liga- 
mentous fibres,  they  present  us  with  two  principal  varieties, 
according  as  they  are  expanded  into  thin  and  broad  plates,  or 
ligamentous  membranes,  or  collected  into  thick  and  elongated 
cords.  The  first  division  includes  fibrous  membranes,  fibrous 
capsules,  tendinous  sheaths,  and  aponeuroses. 

158.  The  jihrous  membranes  resemble  ordinary  membranes, 
but  have,  superadded  to  the  structure  of  the  latter,  numerous 
denser  fibres,  which  gives  them  greater  strength,  and  fit  them  for 
aflfording  mechanical  support  to  various  organs.  Thus,  the  peri- 
osteum of  the  bones  is  a  membrane  of  this  description.  The 
internal  periosteum  of  the  skull  or  dura  mater  has  a  similar 
structure.  The  external  coat  of  the  globe  of  the  eye,  or  sclero- 
tica;  the  investing  membranes  of  many  of  the  glands,  as  ol  the 
kidneys,  belong  to  the  class  of  fibrous  membranes  ;  to  which  also 
we  may  perhaps  refer  some  of  the  coats  of  the  larger  blood- 
vessels, and  of  the  excretory  ducts  of  glands.  Besides  envelop- 
ing organs,  these  fibrous  membranes  often  extend  into  their 
interior,  forming  partitions,  or  even  cells,  which  contribute  to 
their  firmness  and  support. 

159.  The  jihrous  capsules  present  the  form  of  sacs,  which 
surround  certain  joints,  especially  those  of  the  shoulder  and  hip, 
and  preserve  the  connexion  between  the  bones  which  form  these 
joints.  These  capsules,  again,  are  fined  internally  by  serous  or 
synovial  membranes,  supplying  the  fluid  which  lubricates  the 
surfaces  of  the  parts  playing  upon  each  other. 

160.  The  tendinous  sheaths  are  formed  by  fibrous  membranes 
of  a  cylindrical  shape,  which  surround^the  tendons  in  those  parts 
where  they  pass  over  bones,  and  are  particularly  subjected  to 
friction,  or  hable  to  occasional  displacement  during  the  action  of 
the  muscles  which  move  the  joint.  Some  of  these  include  only 
one  tendon  in  their  respective  cavities,  as  those  of  the  fingers 
and  toes :  others  receive  several  tendons,  as  those  belonging  to 
the  muscles  of  the  wrist  and  ankle  joints. 

161.  Aponeuroses  consist  of  extended  sheets  of  fibrous  texture, 
principally  belonging  to  the  organs  of  locomotion  ;  and  disposed 


88  ■  MECHANICAL    FUNCTIONS. 

in  some  instances  so  as  to  forn;i  coverings  of  parts ;  while  in 
others  they  constitute  points  of  attachment  to  muscles.  Thus, 
they  may  be  distinguished  into  aponeuroses  for  enveloping,  and 
aponeuroses  for  insertion.  The  former,  which  are  generally 
termed  fasciae,  either  surround  the  muscles  of  the  limb,  forming 
a  general  sheath  for  it,  as  the  fore-arm  and  thigh ;  or  else  they 
invest  and  confine  some  particular  muscles.  The  aponeuroses 
for  insertion  either  form  broad  or  narrow  surfaces,  or  consist  of 
separate  fibres,  giving  attachment  to  particular  portions  of  mus- 
cles, or  form  arches,  which  both  admit  of  their  connexion  with 
muscular  fibres,  and  at  the  same  time  allow  of  the  passage  of 
vessels. 

162.  The  second  division  compose  the  proper  ligaments  and 
tendons,  all  of  which  have  more  or  less  the  form  of  cords. 

The  ligaments  connect  together  the  articular  surfaces  of  bones, 
and  oppose  a  very  considerable  I'esistance  to  any  force  tending 
to  their  displacement.  The  fibres  which  enter  into  their  compo- 
sition, generally . preserve  a  direction  nearly  parallel;  but  fre- 
quently they  are  extended  in  various  ways,  forming  an  intertexture 
calculated  to  resist  extension  in  different  directions ;  and  from 
their  mere  flattened  form,  bringing  these  ligaments  nearer  to  the 
description  of  fibrous  membranes. 

163.  The  tendons  are  generally  more  simple  in  their  structure, 
consisting  of  elongated  cords;  but  in  some  instances  they  are 
more  complicated,  being  divided  into  several  smaller  cords. 

164.  Bichat*  has  exhibited,  in  the  following  table,  a  general 
view  of  the  preceding  classification  of  what  he  calls  the  fibrous 
system. 

f  cd        [  Fibrous  membranes. 
-Q  g    I  Fibrous  capsules.     . 

1  ^      Fibrous  sheaths,    .      j  General 

2  3    !  C  Fnr  p.nvp 


fM 


TFor  envelop-  ^  Partial. 

I   .  J         ment.        )  General. 

Aponeuroses,         .     <  i^j       u      j        r 

{     r  '  j  f  in  a  broad  surface. 

1^  [For  insertion  ■?  In  an  arch. 

(  In  separate  fibres. 

,  r  •  X  ^  With  rpffular  fasciculi. 

L  Ligaments,         .  <  ^,^^^•^v,  ■  i      f      •     r 

)      ^  (^  With  irregular  fasciculi. 

i  m     J  S  Simple, 

f  Tendons,  .  i  n^^,.i;. 


\  Complicated. 

165.  The  structure  of  all  these  parts,  as  their  name  imports, 
is  essentially  fibrous :  the  individual  fibres  which  compose  them 
being  exceedingly  slender  filaments  of  a  very  dense,  firm,  and 
inelastic  substance  ;  sometimes  parallel  to  each  other,  as  in  the 
tendons  and  ligaments,  and  sometimes  variously  interwoven,  as 

*  See  his  Anatomie  Generale,  torn.  ill.  p.  142. 


ARTICULATION.  89 

in  the  fibrous  membranes.  In  some  portions  of  the  denser  struc- 
tures hereafter  to  be  noticed,  the  fibres  are  so  closely  united  as 
to  present  an  almost  homogeneous  appearance  ;  but  in  all  the 
parts  hitherto  considered,  the  bundles  of  fibres  admit  of  being 
separated  by  maceration;  and  are  resolvable  into  lengthened 
filaments  of  extreme  tenuity.  It  has  not  been  perfectly  ascer- 
tained what  is  the  diameter  of  the  fibres  when  the  subdivision 
has  been  carried  to  its  utmost  hmit ;  but  they  appear  in  this 
ultimate  state  of  division  to  be  as  fine  as  the  filaments  spun  by 
the  silk-worm.  These  ultimate  fibres  are  distinguished  by  their 
flexibility,  their  extreme  tenacity,  and  their  brilliant  whiteness. 
They  are  probably  in  no  case  tubular,  but  soHd  throughout, 
although  Mascagni,  extending  to  them  his  general  system  of 
organic  textures,  regards  them  as  formed  of  lymphatic  vessels. 
Chaussier,*  with  great  appearance  of  truth,  considers  them  as  a 
peculiar  and  primary  organic  tissue,  to  which  he  has  given  the 
name  of  the  albugineous  fibre,  in  order  to  distingush  it  from  the 
mere  simple  cellular  or  membranous  fibre,  which  constitutes  the 
basis  of  the  general  substance  of  the  body. 

166.  The  fibres  which  enter  into  the  composition  of  these 
ligamentous  textures,  are  united  by  a  cellular  tissue  of  extreme 
fineness  and' tenuity,  which  is  rendered  evident  after  maceration 
when  the  ligamentoas  fibres  .are  drawn  asunder.  Their  arrange- 
ment at  the  surface  of  these  structures  is  such  as  to  produce  that 
fflistenipo;  and  satin-like  lustre  which  results  from  a  surface  of 

111 

high  polish  and  density ;  an  appearance  which  is  very  character- 
istic of  the  fibrous  structures.  This  smoothness  and  resplendent 
white  colour  is  possessed  in  the  greatest  degree  by  tendons, 
which  have  in  general  a  greater  extent  of  motion  than  the  liga- 
ments, and  therefore  require  a  higher  degree  of  polish. 


Sect.  III. — Mechanical  Connexions. 

1.  Articulation. 

167.  Having  noticed  the  properties  of  those  elementary  textures 
that  furnish  those  cohesive  and  resisting  forces  which  are  neces- 
sary for  the  mechanical  purposes  of  the  animal  fabric,  we  have 
next  to  review  those  combinations  of  structure  which  have  been 
adopted  for  estabhshing  the  connexions  between  the  various  parts 
of  the  frame,  and  which  adapt  them  to  those  objects.  These 
modes  of  connexion  admit  of  great  variety,  according  to  the  dif- 
ferent mechanical  relations  which  must  take  place  between  them;; 
and  more  particularly  with  reference  to  the  degrees  of  mobility 

'  Dictionnaire  des  Sciences  Medicales.  ,  Organization. 

8* 


90  MECHANICAL    FUNCTIONS. 

which  are  to  result  from  their  union.  In  many  cases  the  parts 
placed  in  juxtaposition  require  to  be  fixed  in  their  places  by  the 
firmest  bonds  which  can  secure  their  relative  immobility :  in 
'others,  the  freest  motion  must  be  allowed ;  while  in  various  other 
instances,  we  find  almost  every  intermediate  degree  of  flexion 
allowed,  and  every  kind  of  connecting  mechanism  employed. 
But  from  the  deep  implanting  of  the  teeth  in  the  jaws,  hke  nails 
firmly  fixed  in  wood,  and  the  mutual  locking  in  of  the  bones  of 
the  skull  by  indented  sutures,  like  the  dove-tailed  junctions  of  car- 
pentry, to  the  freely  rotating  joints  of  the  limbs,  as  in  those  of  the 
shoulder  or  the  hip,  we  may  trace  various  modes  of  articulation 
which  are  calculated  to  limit  the  extent  and  to  regulate  the  kind  of 
movements,  in  subordination  to  particular  ends.  There  is  cer- 
tainly no  part  of  the  human  fabric,  wonderfully  and  fearfully  as  the 
whole  of  it  has  been  made,  which  exhibits  more  palpable  evidences 
of  express  mechanical  contrivance  and  adaptation  to  specific  pur- 
poses, than  the  construction  of  the  joints,  and  of  the  whole  of 
their  auxihary  apparatus.  It  is  well  observed  by  Paley,*  that 
every  joint  is  a  mechanical  curiosity,  and  a  proof  of  contriving 
wisdom.  They  are,  indeed,  as  Cicero  has  truly  expressed  it, 
'"  mirabiles  commissuras,  et  ad  stabilitatem  aptas,  et  ad  artus 
finiendos  accommodatas,  et  ad  motum,  et  ad  omnem  corporis 
actionem. "f 

168.  There  are  two  circumstances  which  determine  the  kind 
of  relative  motion  of  which  a  joint,  by  which  term  is  more  par- 
ticularly meant  the  connexions  of  adjacent  bones,  is  capable. 
The  first  of  these  comprises  the  form  of  the  contiguous  surfaces 
of  the  bones  themselves  which  are  brought  to  play  on  each  other, 
and  their  mode  of  apposition ;  the  second  relates  to  the  structure 
and  mechanical  conditions  of  the  interjacent  flexible  parts,  such 
as  the  ligaments,  the  cartilages,  and  the  membranes,  which  impart 
different  degrees  of  elastibility  or  springiness,  and  variously 
modify  the  motions  which  result.  With  respect  to  the  first,  the 
principal  diversities  arise  from  the  various  extent  of  range  al- 
lowed with  regard  to  the  planes  of  motion ;  and  these  varieties 
are  naturally  distributed  under  two  heads ;  the  one  being  a  semi- 
rotatory  motion  within  a  considerable  extent  of  a  spherical  surface, 
as  exemplified  in  what  are  called  the  ball  and  socket  joints ;  the 
other,  in  which  the  angular  motion  is  restricted  to  a  single  plane, 
as  is  the  case  with  what  are  termed  the  hinge-joints.  It  is  not 
necessary  here  to  advert  to  the  further  distinctions  to  which  a 
minute  examination  of  all  the  different  modifications  of  these 
kinds  of  mechanism,  which  are  exhibited  in  the  solid  structures 
of  the  body,  would  lead  us  ;  which  the  older  physiologists  pursued 
with  great  diligence,  and  which  they  were  fond  of  dignifying 

*  Natural  Theology.  f  De  Natura  Deorum,  1.  ii.  c.  35. 


ARTICULATION.  91 

with  a  formidable  array  of  technical  terms.  It  will  be  sufficient 
for  our  present  purpose  to  observe,  in  general,  that  the  long  bones 
of  the  limbs  have  their  extremities  expanded  so  as  to  form  broad 
surfaces  where  they  are  in  apposition  with  the  contiguous  bones, 
between  which  a  joint  is  formed.  In  the  ball  and  socket  joint, 
it  is  the  moveable  bone  which  has  the  rounded  head,  and  the  fixed 
bone,  or  that  nearest  to  the  trunk  of  the  body,  which  contains 
the  corresponding  cavity  or  socket.  Such  at  least  is  the  case  in 
man ;  but  some  animals  present  us  with  examples  of  a  contrary 
arrangement ;  that  is,  of  the  concave  surface  of  the  moveable, 
turning  on  a  convex  projection  of  the  fixed,  bone.  Bones  of  a 
flat  or  irregular  shape  are,  in  general,  much  more  limited  in  their 
motions,  when  they  form  joints,  than  those  of  a  lengthened  cylin- 
drical form. 

169.  In  proportion  to  the  extent  of  motion  allowed  in  the  joint, 
we  find  provisions  adapted  for  diminishing  friction,  and  guarding 
against  injury.  In  all  the  articulations  the  ends  of  the  bones, 
which  enter  into  their  formation,  are  invested  with  a  smooth  and 
polished  plate  of  cartilage  ;  a  substance  which,  by  its  modified 
hardness,  and  great  elasticity,  is  especially  adapted  to  both  these 
purposes.  Its  limited  degree  of  organization,  also,  gives  it  many 
advantages  in  withstanding  the  influence  of  pressure,  especially 
if  suddenly  made,  and  frequently  repeated.  In  some  joints  this 
investing  layer  of  cartilage  is  of  equal  thickness  throughout,  so 
that  it  appears  as  a  crust,  regularly  moulded  over  the  articular 
surface  of  the  bone  which  it  covers,  and  exactly  preserving  its 
figure ;  but,  in  other  cases,  it  is  found  to  be  thicker  at  the  middle 
than  at  the  marginal  parts;  thereby  increasing  the  convexity  of 
the  projecting  portion,  or  diminishing  the  concavity  of  those 
which  recede ;  both  of  which  appear  to  be  provisions  for  ensuring, 
as  the  case  may  be,  the  uniformity  of  contact  of  the  adjacent 
parts  composing  the  joint.  These  superficial  cartilages,  or  "car- 
tilages of  incrustation,"  as  they  have  been  termed,  appear  to  be 
composed  of  a  multitude  of  slender  fibres,  strongly  adhering 
together,  and  all  of  them  are  perpendicular  to  the  tangential 
planes  of  the  surface  of  the  bone  they  invest,  like  the  pile  of  velvet, 
and  disposed,  therefore,  in  a  manner  very  similar  to  that  of  the 
^bres  of  the  enamel  of  the  teeth,  which  is  superimposed  in  nearly 
the  same  way  on  the  bony  part  of  the  tooth.  The  most  complete 
investigation  of  this  structure  will  be  found  in  a  paper  of  Dr. 
William  Hunter's,  published  in  the  Philosophical  Transactions.* 
It  results  from  this  conformation,  that  the  fibres,  on  the  application 
of  pressure,  yield  to  a  certain  degree,  and  bend  in  waves  :  just 
as  happens  to  velvet  when  it  is  compressed  ;  and  they  again 
resume  their  perpendicular  positions  on  the  removal  of  the  com- 
pressing force. 

*  For  1743,  vol.  42,  p.  544. 


92  MECHANICAL    FUNCTIONS. 

170.  The  whole  of  the  interior  surface  of  each  joint  is  lined 
with  a  smooth  and  glistening  membrane  of  great  tenuity,  forming 
a  cavity  closed  on  every  side,  and  supplying  a  peculiar  secretion, 
termed  the  synovia,  obviously  intended  for  the  lubrication  of  all 
the  contiguous  surfaces.  Similar  synovial  memhranes,  a,s  they 
are  called — forming,  in  like  manner,  closed  sacs — are  met  with, 
surrounding  the  sheaths  of  the  tendons,  and  interposed  between 
other  parts,  the  motions  of  which  would  expose  them  to  con- 
siderable friction.  In  the  former  case,  when  employed  in  the 
articulations,  they  are  termed  capsules  of  the  joints  ;  in  the  latter, 
they  have  received  the  inappropriate  name  of  Bursce  Mucoscb. 
The  synovia  is  a  transparent  and  viscid  fluid,  slippery  to  the  feel, 
and  capable  of  being  drawn  out  into  strings  by  the  fingers.  It 
has  been  imagined,  that  the  secretion  is  principally  derived  from 
certain  fringe-like  processes,  chiefly  visible  in  the  knee  and  hip- 
joints,  and  constituting  what  have  been  called  the  alar  ligainents. 
These  membranous  appendages,  which  project  into  the  cavity  of 
the  joint,  and  appear  to  be  formed  by  folds  of  the  synovial  mem- 
brane, containing  some  cellular  substance,  and  small  pellets  of 
adipose  matter,  present  an  appearance  very  similar  to  that  of  the 
epiploic  duplicatures  of  »*the  peritoneum,  and  especially  of  the 
appendices  epiploiccB  of  the  colon. 

171.  The  motions,  which  a  joint  is  capable  of  performing,  are 
often  modified  and  extended  by  the  interposition  of  detached 
plates  of  cartilage,  connected  only  by  ligament  with  the  synovial 
capsule,  and  capable  of  shifting  their  position,  so  as  to  enlarge 
the  range  and  modify  the  mode  of  action.  Those,  which  we  have 
already  described  under  the  title  of  inter  articular  cartilages,  are 
met  with  chiefly  in  joints  where  the  motion  is  frequent  and  con- 
siderable, and  where  the  ends  of  the  bones  are  subjected  to  great 
pressure  ;  as^in  the  junction  of  the  lower  jaw  with  the  temporal 
bone,  and  in  the  knee-joint.  The  semilunar  cartilages,  in  this 
latter  example,  increase  the  depth  of  the  articular  cavity,  and 
ensure,  in  all  the  motions  of  the  joint,  a  perfect  adaptation  of  the 
surfaces  to  one  another. 

172.  The  bones  are  retained  in  connexion,  their  junction 
strengthened,  and  their  relative  movements  farther  regulated,  by 
the  ligaments  which  invest  the  joint.  Of  these  there  are  two, 
kinds,  the  capsular,  and  the  fascicular ;  the  former  investing  the 
joint  on  all  sides  in  the  case  of  the  ball  and  socket  articulation ; 
and  the  latter  passing  from  bone  to  bone  in  difl^erent  directions, 
limiting  the  motion  more  or  less  to  a  particular  plane.  When,  in 
the  hinge-joint,  they  are  placed  externally  on  the  two  sides,  they 
form  what  are  called  lateral  ligaments ;  but  in  the  case  of  the 
knee,  additional  securities  are  provided,  by  short  and  round  liga- 
ments crossing  one  another  in  the  interior  of  the  joint ;  these  are 
the  crucial  ligaments.     Besides  these,  we  often  find  other  liga- 


PACKAGE    OF    ORGANS.  93 

i;nentous  bands,  passing  more  obliquely,  and  dispersed  in  different 
directions,  which  assist  in  strengthening  the  joint,  preventing  the 
displacement  of  the  bones,  and  thus  completing  the  mechanical 
apparatus  of  each  articulation.  The  muscles,  which  surround 
the  joint,  also  contribute  very  powerfully  in  retaining  the  bones 
in  their  proper  places,  and  preventing  the  sudden  dislocations 
which  might  otherwise  occur  during  the  strains  incident  to  rapid 
and  violent  actions. 

2.  Package  of  Organs. 

173.  The  great  mechanical  objects  of  adhesion  and  support 
being  provided  for  by  the  organic  systems  we  have  now  consi- 
dered, our  attention  may  next  be  directed  to  purposes  of  a  subor- 
dinate and  special  nature,  and  which  relate  to  local  adaptations, 
comprehending  w^hat  Paley  has  aptly  termed  the  package  of  the 
organs.  Art  and  contrivance  have  been  as  manifestly  displayed 
in  fulfilling  these  more  limited  objects,  as  in  the  more  extended 
designs  of  the  general  fabric.  When  we  consider  the  vast  multi- 
plicity of  parts, — requiring  the  study  of  years  of  patient  instruc- 
tion and  dissection  to  be  thoroughly  acquaintedwith, — which  are 
closely  arranged  and  stowed  in  the  narrow  space  allotted  for 
them  in  the  body,  we  cannot  but  be  struck  with  the  care  that  has 
been  taken  in  their  disposal  in  the  most  convenient  manner,  and 
with  the  greatest  economy  of  room.  The  brain  consists  of  a 
prodigious  number  of  fibres,  gathered  together  in  curious  folds, 
or  convolutions,  in  order  that  they  may  occupy  the  smallest 
possible  bulk,  and  be  contained  within  the  circumscribed  cavity 
of  the  skull,  which  is  to  afford  them  protection.  Within  how 
small  a  compass  are  lodged  all  the  delicate  parts  which  compose 
the  complex  organ  of  hearing,  and  which  are  encased  in  a  hollow^ 
space,  scooped  out  of  the  most  solid  parts  of  those  bones  1  Equal 
care  has  been  bestowed  in  the  lodgment  and  package  of  the 
viscera  which  occupy  the  other  cavities  of  the  body,  namely,' the 
thorax  and  abdomen.  Those  which  are  of  greatest  importance 
to  life,  and  whose  delicate  texture  admit  most  easily  of  being 
injured,  are  always  placed  in  situations  of  greatest  security,  and 
effectual  care  is  taken  to  provide  additional  protection  by  means 
of  bones,  cartilages,  or  other  denser  mechanical  fabrics.*  All 
'the  organs  are  tied  down  and  secured  in  their  places  by  mem- 
branes, so  adjusted  in  regard  to  breadth  and  flexibility,  as  to 
allow  of  those  motions  which  their  functions  require  ;  or,  in  other 
cases,  to  retain  their  displacement,  by  tightly  binding  them  in 

*  [This  is  true  in  the  main  ;  j'et  the  abdominal  viscera — wounds  of  which, 
of  the  liver  and  intestines,  for  example,  are  almost  always  fatal — are  contained 
in  a  cavity,  the  anterior  parietes  of  which  afford  very  slender  protection  to 
the  important  contents.] 


94  MECHANICAL    FUNCTIONS. 

their  situation!?.  All  the  important  viscera  &,re  invested  with 
coverings  proper  to  themselves,  composing  capsules,  v^^hich  are 
generally  of  great  density  and  strength,  and  calculated  to  give 
them  effectual  protection  against  pressure  _or  other  mechanical 
causes  of  injury.  The  muscles,  which  are  in  strongest  and  most 
frequent  action,  are  firmly  braced  and  tied  down  by  sheets  of 
fibrous  tissue,  inserted  into  the  neighbouring  bones,  and  prevent- 
ing them  from  starting  from  their  places  when  urged  into  sudden 
and  violent  contractions.  Lastly,  all  the  spaces  intervening 
between  the  muscles,  blood-vessels,  nerves,  and  bones,  are  filled 
up  with  a  quantity  of  cellular  and  adipose  substances,  sufficient 
to  leave  no  vacuity.  Hence  arises  that  rounded  and  flowing 
outline  which  has  been  given  to  the  body,  and  which  forms  one 
of  the  constituent  elements  of  its  beauty. 

174,  The  provision  of  a  general  envelope  to  the  whole  of  this 
complex  system  of  organs,  may  be  regarded  as  another  conside- 
ration which  appertains  to  the  subject  now  before  us,  namely,  the 
package  of  the  body ;  but  its  importance  is  such  as  to  entitle  it 
to  be  treated  under  a  separate  section. 

175.  This  combination  of  structures,  individually  possessing 
different  degrees  of  rigidity,  but  cemented  together  by  a  highly 
elastic  medium,  and  bound  down  by  a  general  envelope  of  con- 
siderable strength,  produces  a  result,  which,  being  of  considerable 
importance  with  reference  to  the  mechanical  condition  of  the 
fabric,  is  deserving  of  special  notice.  It  is  matter  of  observation 
that  the  sum  of  the  cohesive  forces  among  the  particles  conriposing 
the  mass  of  animal  tissues,  is  balanced,  in  the  living  body,  only 
by  the  resistance  arising  from  the  rigidity  or  incompressibility  of 
the  parts  opposed  to  them ;  or,  in  other  words,  the  force  of  elas- 
ticity in  the  cellular  and  membranous  textures  is  not  in  a  state  of 
neutrality,  but  the  equilibrium  is  maintained  only  by  the  mecha- 
nical circumstances  of  situation.  Thus  it  happens  that,  when 
these  circumstances  are  altered,  and  the  equilibrium  disturbed, 
elasticity  comes  into  play  and  produces  a  shrinking  of  the  whole 
mass.  The  result  is  that,  in  the  natural- state,  every  part  is  kept 
on  the  stretch ;  but  retracts  as  soon  as  its  elasticity  is  allowed 
to  act  by  the  removal  of  the  extending  cause.  This  will  happen 
whenever  the  contents  of  hollow  organs  are  withdrawn,  whenever 
the  parts  themselves  are  divided  transversely  by  a  cutting  instru- 
ment, and  also,  when,  by  a  change  of  position,  their  extremities 
are  brought  nearer  together,  and  the  mass  assumes  a  more 
rounded  figure.  This  property,  the  result  of  a  high  degree  of 
unbalanced  elasticity,  has  long  been  known,  though  described 
under  various  names.  The  term  by  which  it  h|as  most  frequently 
been  designated  is  that  of  tone  or  tonicity ;  but  Bicliat,  who  has 
given  a  good  description' of  its  effects,  denominated  it  "  contrac- 
tu itidetissu,^ '  and  "  contractilitepar  difaut  d^ extension,"  whilst 


EXTERNAL    INTEGUMENTS.  95 

he  regards  tonicity  as  anollier  and  distinct  property  not  of  a 
mechanical,  but  of  a  vital  nature.  The  observations  we  have 
formerly  made  on  the  vital  properties,  will  show  that  we  regard 
the  distinction  which  he  here  makes  as  being  founded  on  very 
questionable  grounds. 


Sect.  IV. —  The  Integuments. 
1.   The  External  Integuments. 

176.  The  skin,  which  gives  covering  to  the  whole  body,  toge- 
ther with  its  various  prolongations  and  parts  connected  with  it, 
and  constituting  altogether  the  integuinents,  are  complex  struc- 
tures. They  consist,  in  the  first  place,  of  ordinary  cellular  tis- 
sue ;  secondly,  of  the  same  substance  in  a  more  condensed  and 
membranous  form  ;  and,  thirdly,  of  a  stratum  of  adipose  sub- 
stance ;  but  they  also  present  us  with  a  kind  of  structure  which 
differs  totally  from  any  of  those  we  have  hitherto  had  occasion 
to  notice.  For  the  clear  understanding  of  these  distinctions,  it 
will  be  necessary,  first  to  explain  in  greater  detail  the  composition 
of  the  external  integuments,  or  the  skin. 

The  parts  of  which  skin  consists  are  arranged  in  layers ;  and 
in  giving  an  account  of  these  we  shall  take  them  in  an  order  the 
reverse  of  that  in  which  they  are  usually  considered ;  beginning 
with  the  innermost  layers,  and  proceeding  successively  to  the 
more  external. 

177.  That  portion  of  the  integuments  which  is  called  the  true 
sJ^iny  is  in  most  parts  of  the  body  separated  from  the  adjacent 
muscles  or  bones,  by  a  stratum  of  fat,  or  rather  of  adipose  sub- 
stance ;  that  is,  as  we  have  already  seen,  of  a  cellular  and  vesi- 
cular structure,  containing  the  minute  globules  of  the  fat.  In 
other  parts,  the  attachment  of  the  skin  is  effected  merely  by 
interposed  common  cellular  substance,  of  more  or  less  thickness 
and  density  in  different  places.  The  succeeding  layer  is  that 
which  forms  by  far  the  largest  portion  of  the  integuments,  and 
has  been  denominated  the  corion,  or  the  true  skin.  Its  ultimate 
structure  is  described  by  Haller  as  being  analogous  to  that  ot 
membranous  parts ;  that  is,  composed  of  a  dense  intertexture  of 
short  fibres  and  of  plates,  artificially  interwoven  together,  and 
united  by  the  close  adhesion  of  their  surfaces.  It  may  in  this 
view,  therefore,  be  considered  as  merely  a  denser  tissue  of  the 
common  cellular  substance,  which  is,  in  fact,  the  basis  of  most 
animal  structures.  The  density  increases  gradually  as  we  trace 
the  texture  from  the  inner  to  the  outer  parts  ;  while  at  its  interior 
surface  it  passes  gradually  into  the  looser  cellular  texture  which 
is  beneath  it.     Bichat  gives  a  similar  description  of  the  essential 


96  -  .  MECHANICAL    FUNCTIONS. 

structure  of  the  corion,  but  states  that,  in  addition  to  this,  there 
are  found  a  great  number  of  dense  fibres,  of  a  whiter  colour  than 
the  rest,  interspersed  throughout  its  substance,  which  pass  in  all 
possible  directions,  so  as  of  themselves  to  compose  a  close  net- 
work, and  leave  certain  interstices  or  areolce.  This  reticulated 
texture,  with  the  interposed  vacuities,  may  be  discovered  by 
long-continued  maceration,  which  loosens  the  adhesion  of  the 
fibres.  Small  masses  of  fat  are  found  occupying  the  intervals 
between  them.  Thus  the  dense  fibres  of  the  corion  may  be  re- 
garded as  the  chief  support  or  skeleton,  as  it  were,  of  the  whole 
fabric,  giving  it  its  requisite  form,  consistence,  and  other  mecha- 
nical properties. 

178.  The  external  portion  of  the  corion  is  more  finely  orga- 
nized than  the  rest.  It  has  been  considered  as  forming  a  distinct 
layer  of  the  skin,  named  by  Bichat,  from  the  large  proportion  of 
minute  blood-vessels  it  contains,  the  vascular  net-work  ;  and  by 
•other  anatomists,  corpus  papillare,  from  its  presenting  on  its 
outer  surface,  when  viewed  with  the  microscope,  an  immense 
number  of  little  eminences  or  conical  projections,  which  have 
laeen  termed  papillce.  These  papilige  were  discovered  by  Mal- 
pighi,  and  have  been  since  described  and  delineated  by  Ruysch, 
Albinus,  and  many  other  anatomists.  Cheselden  and  others, 
however,  have  doubted  their  existence,  at  least  as  a  necessary 
appendage  of  the  corion  ;  for  papillae  are  perfectly  visible  to  the 
naked  eye  on  the  upper  surface  of  the  tongue,  where  they  are 
presented  on  a  very  large  scale.  They  are  also  easily  perceived, 
with  a  magnifying  glass,  at  the  tips  of  the  fingers,  as  well  as  in 
other  organs  endowed  with  a  peculiar  sensibility  to  impressions 
of  touch.*  But  in  those  parts  of  the  body  which  have  not  the 
same  sensibility,  and  are  seldom  employed  as  the  vehicles  of 
touch,  they  are  so  minute  as  scarcely  to  admit  of  detection ;  and 
their  existence  has  been  inferred  rather  from  analogy  than  from 
distinct  and  positive  observation. 

179.  The  external  surface  of  the  corion,  or  of  the  corpus 
papillare,  is  covered  with  a  thin  layer  of  a  soft  substance,  which 
Las  been  termed  the  Rete  Mucosum.  It  was  first  observed  by 
Malpighi,  in  the  skin  of  the  negro,  and  is  hence  often  called  after 
him  the  Rete  Malpighianum.  The  structure,  and  even  existence 
of  this  membrane  have  given  occasion  to  much  controversy. 
Malpighi  had  announced  it  as  being  a  stratum  of  soft  matter, 
disposed  in  the  form  of  lines  which  crossed  one  another  in  various 
directions.  Blumenbach  and  other  anatomists  describe  it  as 
merely  a  thin  layer  of  pulpy  matter,  without  any  distinct  reticulated 
structure.     Bichat,  on  the  other  hand,  denies  altogether  its  ex- 

*  [Breschet  (^Nouvelles  Recherches  sur  la  structure  de  la  Peau,  Paris,  1835) 
calls  the  corpus  papillare  the  '  Neurothelic  Apparatus.'] 


EXTERNAL    INTEGUMENTS.  97 

istence  as  a  proper  membrane,  and  supposes  that  what  Malpighi 
saw  and  described  is  merely  a  collection  of  very  delicate  vessels, 
which,  after  having  passed  through  the  corion,  form  a  net-work 
on  its  surface.  In  this  opinion  he  is  supported  by  other  anatomists 
of  high  authority,  as  Chaussier  and  Rudolphi.  Mr.  Cruickshank,* 
on  the  contrary,  who  bestowed  great  pains  on  the  examination 
of  this  subject,  entertains  no  doubt  of  the  existence  of  the  rete 
mucosum,  both  in  the  external  skin,  and  also  even  in  some  of  its 
productions  in  the  interior  of  the  body.  Dr.  Gordon  admits  of 
the  presence  of  the  rete  mucosum  in  the  skin  of  the  negro,  where 
it  is  easily  demonstrated  ;  but  asserts  that  it  cannot  be  found  in 
that  of  the  European.  On  the  whole,  the  positive  evidence  in 
favour  of  the  real  existence  of  this  membrane  appears  to  pre- 
ponderate ;  and,  at  any  rate,  it  seems  admitted  on  all  hands,  that 
the  colouring  matter  of  the  skin,  which  is  black  in  the  negro,  and 
has  different  tints  in  the  other  varieties  of  the  human  race,  is 
situate  in  that  part  which  has  been  assigned  as  the  seat  of  the 
rete  mucosum.  By  some  it  has  been  stated  that  the  rete  mucosum 
extends  in  a  uniform  layer  over  the  whole  surface  of  the  true 
skin  ;  by  others  that  it  is  perforated  in  various  parts  by  the  papillae 
of  the  corion,  and  exists  only  in  the  interstices  of  these  papillae.* 

180.  The  outermost  layer  of  the  skin  is  the  cuticle  or  epider- 
mis, which  gives  a  uniform  covering  to  every  part  of  its  surface, 
adhering  closely  to  it,  and  being  accurately  applied  to  all  its 
inequalities.  It  adheres  with  considerable  tenacity  to  the  subjacent 
skin,  through  the  medium  of  the  rete  mucosum,  and  its  attachment 
is  perhaps  also  secured  by  fibres  passing  from  the  one  to  the 
other.  In  the  dead  skin  a  separation  is  easily  effected  by  macer- 
ation in  water,  and  by  a  state  of  incipient  putrefaction.  In  the 
living  body  the  cuticle  is  detached  by  the  operation  of  a  blister, 
or  by  scalding  water,  which  produce  an  effusion  of  serous  fluid 
on  the  outer  surface  of  the  corion.  As  the  cuticle  is  impervious 
to  this  fluid,  it  is  raised,  and  gives  rise  to  a  permanent  vesicle. 

181.  When  the  cuticle  is  carefully  separated  from  the  corion, 
after  its  connexion  has  been  loosened  by  putrefaction,  a  multitude 
of  very  slender  transparent  filaments  are  seen,  stretching  between 
these  two  layers,  which  are  torn  asunder  when  farther  extended. 
Dr.  William  Hunter  believed  these  filaments  to  be  the  terminations 
of  those  vessels  which  exhale  the  perspiration,  and  nearly  the 
same  views  have  been  entertained  with  regard  to  their  nature 

*  On  Insensible  Perspiration. 

f  [Breschet  (Op.  citat.')  affirms,  that  there  is  a  special  <■' chromafngenous 
apparatus''''  for  producing  the  colouring  matter,  composed  of  a  glandular  or 
secreting  parenchyma,  situate  a  little  below  the  papillae,  and  presenting  par- 
ticular excretory  canals,  which  pour  out  the  colouring  matter  on  the  surface 
of  the  derma.] 

9 


Ho  MECHANICAL    FUNCTIONS. 

by  Bichat  and  by  Chaussier.     Cruickshank,  on  the  contrary,  con- 
sidered them  to  be  processes  from  the  cuticle,  and  not  vessels. 

182.  Many  erroneous  notions  have  atdifierent  times  prevailed 
with  respect  to  the  intimate  structure  of  the  epidermis.  Lee- 
wenhoeck  conceived  that  it  is  composed  of  a  number  of  laminae, 
or  scales,  which  he  represented  as  having  an  imbricated  arrange- 
ment, that  is,  overlapping  each  other  successively,  like  the  scales 
of  a  fish.  But  it  is  now  generally  admitted  that  this  M'as  a  de- 
ceptive appearance.  The  division  of  layers,  which  it  may  seem 
to  admit  of  in  parts  where  it  is  of  unusual  thickness,  is  merely  an 
artificial  separation,  not  warranted  by  any  natural  distinction  of 
textures.  Although  some  have  pretended  to  discover  in  it  a 
congeries  of  vessels,  especially  Ij'mphatics,  yet  the  most  accurate 
and  unbiassed  observers  declare  that  they  cannot  perceive  in  the 
epidermis,  a  specific  texture  of  any  kind  or  any  regular  arrange- 
ment of  its  parts.  Dr.  Gordon  gives  it  as  his  decided  opinion 
that  it  is  "truly  inorganized,  and  non-vascular."* 

183.  Leewenhoeck  imagined  also  that  he  could  discern  a 
number  of  perforations,  or  pores,  as  he  termed  them,  in  the 
cuticle.  But  later  and  more  scrupulous  inquirers  have  looked  in 
vain  for  these  supposed  pores;  and  it  is  now  generally  admitted 
"that  none  such  exist.     Indeed,  one  of  the  most  characteristic 

properties  'of  the  cuticle  is  its  impermeability  to  fluids,  under 
ordinary  circumstances.  The  latest  inquiries  into  this  subject 
are  those  of  Mr.  Chevalier.f  who  describes  the  cuticle  as  com- 
posed of  an  infinite  number  of  small  vdamina,  regularly  arranged, 
so  as  to  form  a  bibulous  and  exquisitely  hygrom.etrical  covering.J 
The  mode  in  which  the  occasional  transmission  of  fluids  through 
this  substance  takes  place  in  cutaneous  absorption,  and  perspira- 
tion, will  be  the  subject  of  future  discussion.  The  only  real  dis-' 
tinguishable  pores  in  the  cuticle  are  those  which  give  passage 
to  the  hairs,  and  to  the  sebaceous  follicles  hereafter  to  be  noticed. 
'  Thus,  then,  there  is  presented  to  us  in  this  layer  of  the  integu- 
ment, a  kind  of  structure  differing  essentially  from  either  the 
cellular  or  membranous  tissues  which  have  already  been  des- 
cribed. The  epidermis  is  an  animal  texture,  nearly  homogeneous 
in  its  substance,  possessing  but  amoderate  degree  of  extensibility, 
and  approaching  to  the  nature  of  an  inorganic  substance,  inas- 
much as  it  exhibits  no   appearance   of  vascularity,  and  a  total 

*  [The  researches  of  the  Investigators,  referred  to  in  the  third  note,  have  ex- 
hibited that  the  tissue  of  the  epidermis  is  complex,  -and  that  its  organization  is 
connected  with  the  functions  of  exhalation  and  absorption.  Its  vitality,  if 
any  it  possess,  has  been  compared  to  that  of  the  vegetable.] 

t  Lectures  on  the  General  Structure  of  the  Human  Body,  p.  133. 

X  [Still  later  investigations  have  been  made  by  MM.  Breschet  and  Roussel 
de  Vauzeme,  {Op.  citat.)  by  Wendt  {MuUei-''s  Jrchiv.  1834,)  and  Von 
(lurlt,  (Ibid.  1835.)  which  have  thrown  considerable  light  on  its  structure. 
See,  also,  British  and  Foreign  Med.  Review,  ii.  429. 


EXTERNAL    INTEGUMENTS.  90 

absence  of  nerves,  or  other  medium  of  connexion  with  the  Hving 
system.  Bichat  even  considers  its  vitality  as  exceedingly  ob- 
scure; he  doubts  whether  it  can  be  said  to  possess  life;  but  is  in- 
clined to  regard  it  as  a  semi-organized,  or  rather  inorganic  body, 
placed  by  nature  at  the  point  of  communication  between  external 
dead  matter  and  the  living  skin,  and  serving  as  a  gradation  be- 
tween them.* 

184.  The  nails  and  the  hair  are  to  be  classed  as  structures 
very  similar  to  the  epidermis,  of  which,  indeed,  they  are  often 
regarded  as  mere  appendages.  The  nails,  in  particular,  have  so 
intimate  an  adhesion  to  the  epidermis,  that  both  are  generally 
detached  together,  by  maceration.  They  consist  of  hard,  trans- 
parent, and  semi-elastic  plates,  formed  of  a  substance  analagous 
to  the  horns  of  animals.  They  adhere  to  the  subjacent  corion, 
(which  is  in  those  parts  furnished  with  a  great  abundance  of 
minute  blood-vessels,  and  of  which  the  papillas  are  arranged  in 
longitudinal  and  parallel  rows,  very  close  to  one  another,)  in  a 
manner  similar  to  that  in  which  the  epidermis  adheres  to  the 
corion  in  other  parts.  The  internal  surface  of  the  nail  is  soft, 
pulpy,  and  marked  with  longitudinal  grooves  corresponding  to 
the  lines  which  they  cover  and  enclose;  and  by  this  mutual 
adaptation  the  connexion  between  them  is  extremely  intimate. 
The  innermost  edge  of  the  nail  is  received  into  a  groove  formed 
of  a  duplicature  of  skin  fitted  for  its  reception.  The  epidermis 
belonging  to  this  portion  of  skin  is  folded  back  upon  it,  and  on 
arriving  at  the  root  of  the  nail,  quits  the  corion,  is  reflected  over 
the  external  surface  of  the  nail,  and  becomes  identified  with  its 
substance. 

The  nails,  in  all  their  mechanical  properties,  correspond  to  the 
cuticle,  and  may  be  regarded  as  the  same  substance  in  a  greater 
state  of  condensation. 

The  hair  consists  of  slender  filaments,  which  appear  to  bd  formed 
of  nearly  the  same  substance  as  the  nails,  and  may  be  considered, 
in  a  mechanical  point  of  view,  as  still  mor^.  condensed  forms  of 
cuticle.  Each  hair  is  provided  at  its  root,  with  an  expanded  por- 
tion, or  bulb,  from  which  its  extension  proceeds,  and  which  by 
the  intervention  of  its  vessels,  connects  it  with  the  corion,  in 
which  it  is  imbedded,  just  as  the  roots  of  a  vegetable  attach  it  to 
the  soil.  The  strength  of  hair  is  exceedingly  great,  compared 
with  its  small  diameter,  as  has  been  frequently  ascertained  by 
trying  the  weights  which  it  can  support  without  tearing.  There 
is  no  substance,  indeed,  which  would  be  better  adapted  for  making 

*  [Breschet  affirms,  that  there  is  a  special  bhnnngenous  apparatus  for  the 
secretion  of  the  mucous  matter  constitulinij  the  epidermis,  which  is  composed 
ofa  glandular  parenchyma  or  organ  of  secretion,  situate  in  the  substance  of  the 
derma,  and  of  excretory  ducts,  which  issue  from  the  organ,  and  deposite  the 
mucous  matter  between  the  papillae.] 


100  MECHANICAL    FUNCTIONS. 

ropes  than  human  hair,  provided  it  could  be  procured  of  sufficient 
length.  It  scarcely  possesses  any  extensibility,  and  is  consequently 
inelastic.  If  exposed  to  moisture,  it  imbibes  a  certain  quantity 
of  water ;  and  this  absorption  is  accompanied  with  an  increase 
in  the  length  of  the  hair.  From  its  having  this  property,  it  has 
been  employed  by  De  Saussure  as  a  hygrometer,  or  instrument 
for  indicating  the  degree  of  moisture  or  dryness  of  the  atmosphere. 
In  order  to  adapt  it  to  this  purpose,  however,  it  requires  to  be 
freed  from  a  quantity  of  oily  matter,  which  it  naturally  contains, 
by  maceration  in  an  alkaline  solution.  The  colouring  matter  of 
the  hair  is  supposed  to  correspond  in  its  nature,  as  it  does  in  its 
appearance,  to  that  which  is  contained  in  the  rete  mucosum  of 
the  skin. 

Thus  we  find  that  there  is  a  very  considerable  similarity  be- 
tween the  hair,  the  nails,  and  the  cuticle,  with  regard  both  to 
structure,  composition  and  mechanical  properties  ;  and  that  they 
may  be  regarded,  when  once  their  formation  has  been  completed, 
as  equally  devoid  of  vascularity,  and  as  possessed  of  the  lowest 
degrees  of  organization  and  vitality  ;  if,  indeed,  these  latter  pro- 
perties can  at  all  be  attributed  to  them. 

2.  Of  the  Internal  Integuments,  or  the  Mucous  Membranes. 

185.  The  structure  which  characterises  the  external  integu- 
ments is  continued  in  various  places  into  the  internal  parts ;  and  is 
found,  with  certain  modifications,  in  all  those  membranes  which 
line  the  internal  surfaces  of  cavities  or  channels  having  an  exter- 
nal opening.  This  is  the  case  with  the  whole  track  of  the  alimen- 
tary canal;  including  the  mouth,  pharynx,  oesophagus,  stomach, 
and  intestines.  It  is  exemplified,  also,  in  all  the  passages  of  the 
air  in  respiration,  as  the  nostrils,  larynx,  trachea  or  wind-pipe, 
bronchia  or  air-tubes,  and  the  air  vesicles  of  the  lungs.  All  those 
passages  which  open  externally,  such  as  those  of  the  ears,  urethra, 
and  vagina,  are  like^se  defended  by  a  lining  of  mucous  mem- 
brane. 

186.  Bichat  has  considered  the  mucous  membranes  as  forming 
a  distinct  system  of  structure.  Analogous  in  many  respects  to 
the  serous  membranes,  they  present,  in  others,  the  most  marked 
differences.  They  agree  in  their  office  of  affording  protection  to 
the  organs  to  which  they  are  attached ;  and  their  structure,  in  as 
far  as  it  is  chiefly  resolvable  into  condensed  cellular  tissue,  is 
very  similar.  But  as  they  have  to  serve  the  additional  office  of 
defending  the  parts  which  they  invest  against  the  irritating 
qualities  of  the  substances  that  may  come  in  contact  with  them, 
and  which  may  be  either  the  external  air  or  the  food,  or  extra- 
neous bodies,  received  from  without ;  or  else  secretions  formed 
hy  the  internal  organs,  which  are  to  be  conducted  to  the  surface, 


INTERNAL    INTEGUMENTS.  101 

it  was  necessary  that  the  fluid  which  covered  them  should  have 
properties  adapted  to  this  ohject. 

187.  We  find,  accordingly,  that  instead  of  the  watery  liquid 
which  exudes  from  serous  membranes,  the  mucous  membranes 
prepare  a  secretion  containing  a  large  proportion  of  mucus. 
Hence  a  more  complicated  structure  is  required  in  the  mucous 
than  in  the  serous  membranes.  They  are  divisible  into  several 
layers;  that  which  connects  them  with  the  parts  surrounding 
the  passage  or  cavity  which  they  line,  is  of  a  denser  structure  ; 
while  the  one  which  forms  the  inner  surface  of  the  cavity  is 
softer,  and  somewhat  pulpy  in  its  consistence.  Its  surface  is 
beset,  in  many  parts,  with  numerous  minute  processes,  or  villi^ 
as  they  are  termed.  These  have  been  supposed  to  bear  some 
analogy  to  the  papillce  of  the  corion  ;  and  the  general  corres- 
pondence of  the  structure  of  the  mucous  membrane  and  of  the 
external  integuments  has  been  farther  pursued  in  the  examina- 
tion of  the  fine  pellicle  which  gives  a  universal  covering  to  the 
pulpy  portion,  and  which  has  been  assimilated  to  the  cuticle. 
There  can  be  no  doubt  that  the  cuticle  belonging  to  the  skin  is 
continued  over  the  membranes  which  line  many  of  the  passages 
above  enumerated,  and  may  be  traced  for  a  considerable  way  in 
those  passages.  As  wo  advance  farther,  this  cuiicular  covering 
becomes  gradually  thinner,  till  it  ceases  to  be  perceptible. 

188.  But  the  circumstance  which  more  especially  character- 
ises the  mucous  membranes,  is  the  presence  of  a  number  of  small 
cavities,  crypts  ov follicles  as  they  are  called;  which  have  more 
or  less  of  a  spheroidal  shape,  and  which  open  upon  the  surface  of 
the  membrane  by  a  distinct  orifice,  or  duct  of  communication. 
These  minute  sacs  or  follicles  are  themselves  lined  with  an 
extremely  fine  cuticular  membrane,  derived  from  the  general 
covering  of  the  surface  on  which  they  are  met  with.  They  are 
found  filled  with  mucus,  and  are  therefore  considered  as  the 
sources  whence  that  secretion  is  principally  derived. 

189.  Follicles  of  a  similar  structure  are  found  in  the  various 
parts  of  the  skin ;  but  the  substance  which  they  produce,  and 
which  they  effuse  upon  the  surface  of  the  skin,  is  more  of  an  oily, 
than  of  a  mucous  nature.  It  has  been  termed  sebaceous  matter ; 
and  the  small  cavities  which  prepare  this  matter,  are  known  by 
the  name  of  the  sebaceous  glands  ov  follicles. 

190.  Thus  it  appears,  that  although  the  offices  of  the  external 
integuments  of  the  internal  mucous  membranes  are  sufficiently 
distinct,  yet  a  general  analogy  exists  between  them  in  many 
points  of  their  structure,  sufficient  to  justify  their  being  arranged 
under  the  same  order,  in  a  general  classification  of  animal  struc- 
tures. 

9* 


102  MECHANICAL    FUNCTIONS. 


Sect.  I V. — Muscular  Action. 


191.  Having  now  considered  the  system  which  constitutes  the 
passive  instrunnents  of  the  fabric,  it  is  time  that  we  direct  om' 
attention  to  the  active  powers  which  are  the  sources  of  motion, 
and  the  springs  of  animation  and  of  energy  in  the  Uving  body. 

192.  As  in  an  extensive  system  of  machinery,  economy  is  best 
consulted  by  the  employment  of  a  single  moving  power,  such  as 
a  fall  of  water,  the  impulse  of  the  wind,  the  current  of  a  river, 
or  the  force  of  steam,  so,  in  the  animal  economy,  nature  has 
provided  the  muscular  power,  and  applied  it  in  every  instance 
where  great  mechanical  power  was  required  to  accomplish  the 
intended  object.  But  before  inquiring  into  the  nature  of  this  new 
animal  power,  it  will  be  necessary  to  consider  the  properties  of 
those  organs,  the  muscles,  in  which  this  power  appears  to  reside. 

1.  Structure  of  Muscles. 

193.  Muscles  are  organs  composed  of  certain  fibres,  endowed 
with  a  peculiar  power  of  contracting  in  their  length,  under  certain 
circumstances.  These  fibres  are  generally  disposed  in  a  parallel 
direction,  and  variously  united  together  by  intervening  cellular 
substance.  The  muscular  system  forms  a  large  proportion  of  the 
weight,  and  certainly  the  greater  part  of  the  bulk  of  the  human 
body. 

194.  On  examining  the  structure  of  a  muscle,  we  find  the 
minuter  fibres  are  every  where  surrounded  by  a  fine  cellular 
texture,  which  connects  them  together  into  bundles,  which  have 
been  called  fasciculi.  These  bundles  are  connected  to  each  other 
by  coarse  cellular  membrane,  so  as  to  form  fasciculi  of  larger 
size :  these,  again,  are  united  together  into  still  larger  fasciculi 
by  a  still  more  loose  cellular  tissue.  This  system  of  package  is 
continued  until  we  arrive  at  large  cylindrical  bands  of  fibres, 
which  have  been  termed  lacerti,  and  which,  being  applied  laterally 
to  each  other,  and  covered  by  a  general  investment  of  membrane, 
compose  the  entire  muscle.  The  fasciculi,  as  well  as  the  cellular 
membrane,  are  coarser  in  some  muscles  than  in  others.  Thus 
they  are  thicker  in  the  large  muscles  of  the  limbs,  than  in  the 
delicate  muscles  appropriated  to  the  eye,  and  other  organs  of 
sense.  The  structure  which  has  now  been  described  is  easily 
discovered  in  a  portion  of  muscle  which  has  been  cut  transversely, 
and  then  boiled  for  some  time,  or  macerated  in  alcohol. 

195.  Physiologists  have  not  contented  themselves  v/ith  these 
general  views  of  the  structure  of  muscles,  but  have  been  sohcitous 
to  ascertain  the  nature  and  dispositions  of  the  ultimate  fibres  to 
which  muscles  owe  their  characteristic  properties.     The  micro- 


STRUCTURE  OF  MUSCLES.      ,  103 

scope  has  been  resorted  to  for  this  purpose  ;  but  the  success  of 
those  observers  who  have  trusted  to  this  instrument  in  establishing 
any  certain  facts,  has  by  no  naeans  corresponded  with  the  dih- 
ge'nce  and  zeal  with  which  they  have  engaged  in  the  inquiry. 
We  find  in  this,  as  in  nnany  other  subjects  where  the  appearances 
resulting  from  the  employment  of  very  high  magnifying  powers 
are  the  objects  of  research,  that  the  greatest  discordance  prevails 
among  the  accounts  given  by  different  observers.  Leewenhoeck, 
who  was  one  of  the  first  who  applied  the  microscope  to  the  in- 
vestigation of  the  intimate  structure  of  organized  bodies,  but 
who  was  too  often  led  away  from  the  truth  by  the  ardour  of  his 
imagination,  describes  the  ultimate  muscular  fibres,  or  those 
which  admit  of  no  further  mechanical  division  without  a  separa- 
tion of  their  substance,  as  being  almost  inconceivably  minute. 
He  states  them  to  be  many  thousand  times  smaller  than  a  fibre 
which  would  only  be  just  visible  to  the  naked  eye.  He  represents 
them  as  cylindrical  in  their  shape,  and  parallel  to  each  other,  but 
pursuing  a  serpentine  course.  He  remarks  that  they  are  of  the 
same  figure  in  all  animals,  although  differing  considerably  in  their 
diameter  in  difierent  animals,  and  that  without  any  relation  to 
the  size  of  the  animal.  He  observed,  for  example,  that  the  fibril 
of  the  frog  was  larger  than  that  of  the  ox. 

196.  Muys,  a  Dutch  anatomist,  who  was  engaged  for  a  period 
of  twenty-five  years  in  the  most  laborious  researches  on  this  sub- 
ject, arrived  at  a  very  different  result  from  Leewenhoeck ;  for 
he  concludes  that  the  real  ultimate  fibrils  of  muscles  are  in  all 
cases,  even  when  the  comparison  was  extended  to  animals, 
exactly  of  the  same  size. 

197.  Among  the  more  modern  anatomists,  Prochaska*  has 
bestowed  the  greatest  care  in  the  examination  of  this  subject; 
and  his  account  has  every  appearance  of  being  entitled  to  our 
confidence.  He  states  expressly  that  the  muscular  fibrils  are 
not  all  of  the  same  diameter,  but  differ  in  different  animals,  and 
even  in  different  parts  of  the  same  animal.  Each  individual 
fibril,  however,  when  carefully  separated  from  all  extraneous 
matter,  is  of  uniform  thickness  throughout  its  whole  extent,  and 
perfectly  continuous,  even  in  the  longest  muscles,  from  one  end 
to  the  other.  He  confidently  asserts  that  they  are  solid ;  and 
instead  of  being  cylindrical,  that  they  have  a  prismatic,  or  poly- 
hedral shape,  generally  flattened,  or  thicker  on  one  side  than  on 
the  other  ;  a  transverse  section  of  the  muscle  thus  presenting  the 
appearance  of  basaltic  columns  in  miniature.  Their  diameter  is 
stated  to  be  about  the  fiftieth  part  of  that  of  the  globules  of  the 
blood.  Their  surface  was  found  to  present  a  number  of  depres- 
sions or  wrinkles  ;  a  circumstance  which  gives  them  a  serpentine 

''^De  Came  Musculari. 


104  MECHANICAL    FUNCTIONS. 

appearance.  These  transverse  lines  he  attributes  to  the  numerous 
blood-vessels,  nerves,  and  membranous  bands  which  cross  the 
fibrils  at  different  points. 

198.  According  to  Hooke  and  Swammerdam,  the  muscular 
fibrils  are  composed  of  a  series  of  globules.  Other  physiologists, 
such  as  Cowper  and  Stuart,*  whose  observations  appear  to  have 
been  influenced  by  preconceived  theories,' imagined  that  they 
were  cellular.  Borelli,t  who  was  also  biassed  by  his  favourite 
hypothesis,  believed  them  to  be  composed  of  a  series  of  rhomboidal 
vesicles.  The  Abbe  FontanaJ  in  general  agrees  with  Prochaska 
in  his  representation  of  muscular  fibrils.  He  remarks  that  they 
are  furnished  with  transverse  bands  at  regular  intervals,  and  that 
they  may  always  be  distinguished  by  their  parallel  disposition 
from  the  fibres  of  membrane,  which  are  more  or  less  contorted. 

Sir  Anthony  CarUsle§  states  that  a  muscular  fibre  duly  pre- 
pared, by  washing  away  all  adhering  extraneous  substances,  and 
viewed  by  a  powerful  microscope,  appears  to  be  a  solid  cylinder, 
the  covering  of  which  is  a  reticulated  membrane,  and  the  con- 
tained part,  a  dry  pulpy  substance,  irregularly  granulated  and  of 
little  cohesive  power  when  dead. 

199.  Mr.  Bauer,||  who  is  one  of  the  latest  authorities  on  this 
subject,  represents  the  ultimate  muscular  fibrils,  as  composed 
of  a  row  of  globules,  exactly  corresponding  in  size  to  those  of 
the  blood  when  deprived  of  their  colouring  matter ;  that  is, 
about  the  five-thousandth  part  of  an  inch.  By  long  maceration 
in  water,  he  finds  that  the  mutual  coesion  of  these  globules  is 
loosened,  and  the  fibre  is  consequently  broken  down  and  resolved 
into  a  mass  of  globules.  The  general  results  of  Mr.  Bauer's 
observations  were  confirmed  by  various  observers  an  France, 
such  as  Dr.  Edwards,  and  by  Messrs.  Prevost  and  Dumas,  Beclard 
and  Dutrochet. 

200.  On  the  other  hand,  the  more  recent,  and  apparently  ac- 
curate researches  of  Dr.  Hodgkin  and  Mr.  Lister,1[  and  subse- 
quently those  of  Mr.  Skey,**  have  clearly  shown  that  the  supposed 
globular  structure  of  the  muscular  fibre  is  a  mere  optical  decep- 
tion, arising  from  deficient  defining  power  in  the  microscope 
employed ;  and  that  the  fibre  is  continuous  throughout  its  whole 
length,  and  sometimes  marked  by  transverse  stri^,  which  occur 
at  intervals  much  smaller  than  the  diameter  of  the  fibre  itself 
They  have  also  pointed  out  this  circumstance  as  constituting  a 
remarkable  distinction  between  the  muscles  of  voluntary  and 

*  Dissertatio  de  Structura  et  Motu  Musculari. 

t  De  Motu  Animalium.  X  ^"''  ^^s  Poison?. 

§  Philosophical  Transactions  for  1805.  _  ||  Ibid,  for  1818,  p.  164. 

"if  Appendix  to  Dr.  Hod^kin's  translation  of  Dr.  Edwards's  work,  "  De 
I'lnfluence  des  Agens  Physiques  sur  la  Vie." 

**Philosophical  Transactions  for  1837,  p.  371.  t 


MUSCULAR    CONTRACTILITY.  105 

those  of  involuntary  motion,  with  regai'd  to  this  striated  struc- 
ture; for  it  is  only  the  fibres  of  the  former  which  are  charac- 
terized by  innumerable  very  minute,  but  clear  and  fine  parallel 
lines,  or  strias,  which  cross  the  fibre  transversely.  Mr.  Skey 
concludes  from  his  researches,  that  these  fibres  in  man  have  an 
average  diameter  of  one  four-hundredth  of  an  inch,  and  that 
they  are  surrounded  by  transverse  circular  striae  varying  in 
thickness,  and  in  the  number  contained  in  a  given  space.  He 
describes  these  stria)  as  constituted  by  actual  elevations  on  the 
surface  of  the  fibre,  with  intermediate  depressions,  considerably 
narrower  than  the  diameter  of  a  globule  of  blood.  Each  of  these 
muscular  fibres,  of  which  the  diameter  is  one  four-hundredth  of 
an  inch,  is  divisible  into  bands  of  fibrillse,  each  of  which  is  again 
subdivisible  into  one  hundred  tubular  filaments,  arranged  parallel 
to  one  another  in  a  longitudinal  direction,  around  the  axis  of  the 
tubular  fibre  which  they  compose,  and  which  contains  in  its 
centre  a  soluble  gluten.  The  partial  separation  of  the  fibrillce 
gives  rise  to  the  appearance  of  broken  or  interrupted  circular  striae, 
which  are  occasionally  seen.  The  diameter  of  each  filament  is 
one  sixteen-thousandth  of  an  inch,  or  about  a  third  part  of  that 
of  a  globule  of  the  blood.  On  the  other  hand,  the  muscles  of  invo- 
luntary motion,  (or  as  Bichat  would  term  them,  of  organic  life)  are 
composed,  not  of  fibres  similar  to  those  above  described,  but  of 
filaments  only;  these  filaments  being  interwoven  with  each  other 
in  irregularly  disposed  lines  of  various  thickness,  having  for  the 
most  part  a  longitudinal  direction,  but  forming  a  kind  of  untrace- 
able net-work.  They  are  readily  distinguishable  from  tendinous 
fibres,  by  the  filaments  of  the  latter  being  uniform  in  their  size, 
and  pursuing  individually  one  unvarying  course,  in  lines  parallel 
to  one  another.  The  fibres  of  the  heart  appear  to  possess  a 
somewhat  compound  character  of  texture.  The  muscles  of  the 
pharynx  exhibit  the  character  of  the  muscles  of  voluntary  mo- 
tion ;  whilst  those  of  the  oesophagus,  the  stomach,  the  intestines, 
and  the  arterial  system,  possess  that  of  the  muscles  of  involuntary 
motion.  The  determination  of  the  exact  nature  of  the  muscular 
fibres  of  the  iris,  presented  considerable  difficulties,  which  Mr. 
Skey  was  not  able  satisfactorily  to  overcome. 

2.  Muscular  Contractility. 

201.  The  proper  muscular  fibre  is  so  completely  surrounded 
by  cellular  membrane,  and  is  of  so  small  a  diameter,  that  it  is 
scarcely  possible  to  determine  with  accuracy  its  physical  proper- 
ties, independently  of  those  of  the  tissue  in  which  it  is  imbedded. 
The  contractile  power  with  which  it  is  endowed,  can  be  studied 
only  as  its  effects  are  exhibited  by  collections  of  fibres,  such  as 
those  which  constitute  the  muscles ;  although  in   these  it  must 


106  MECHANICAL    FUNCTIONS. 

obviously  be  combined  with  the  elastic  power  of  the  cellular 
texture  entering  into  its  composition. 

202.  It  will  soon  be  evident,  however,  that  the  property  by 
which  the  muscular  fibre  is  eminently  characterised,  is  that  of 
suddenly  contracting  in  its  length,  and  thus  of  bringing  the  two 
ends  of  the  muscle,  and  the  parts  to  which  those  ends  are 
attached,  nearer  to  each  other.  This  contraction  is  produced 
with  astonishing  quickness  and  force,  overcoming  considerable 
resistances,  and  raising  enormous  weights.  It  is  generally  the 
effect  of  the  will  of  the  animal  to  move  the  parts  to  which  the 
muscle  is  attached ;  but  it  may  also  be  excited  by  other  causes. 
The  agent  which  thus  produces  muscular  contraction  is  called  a 
stimuhts. 

203.  Under  the  appellation  of  stimuli,  are  included  many  things 
which  seem  scarcely  to  have  any  property  in  common,  except 
that  of  acting  upon  the  muscular  fibres,  either  directly,  or  through 
the  medium  of  the  nerves  which  supply  them.  The  contact  of 
many  bodies  will  produce  this  efi'ect  by  mere  mechanical  impulse, 
independently  of  any  other  quality  they  may  possess.  Whatevet 
occasions  a  mechanical  injury  to  the  texture  of  the  muscle  or 
nerve,  or  an  actual  breach  of  substance,  such  as  the  puncture, 
division,  or  laceration  of  the  fibres,  will  immediately  excite  mus- 
cular contraction.  This  effect  also  results  from  tlie  application 
of  any  substance  exerting  a  chemical  action  on  the  part;  a  class 
of  stimuli  which  comprehends  a  great  variety  of  agents,  such  as 
acids,  alkalies,  and  most  of  the  salts  which  they  form  by  their  mutual 
combinations,  as  also  the  earthy  and  metallic  salts,  alcohol,  the 
volatile  oils ;  and  above  all,  oxygen,  either  in  the  form  of  gas,  or 
when  contained  in  substances  that  part  with  it  readily.  Even 
water  itself  seems  to  have  some  corrugating  power  when  it  is 
applied  directly  to  the  muscular  fibre ;  its  action,  however,  is 
much  increased  by  minute  quantities  of  salt  which  it  may  hold  in 
solution.  Thus  it  is  found  that  hard  water  promotes  the  contrac- 
tion of  the  muscles  of  fish  that  have  been  crimped  more  than 
fresh  water;  and  a  similar  difference  of  eflect  is  often  observed 
in  boiling  meat  in  soft  or  in  hard  water. 

204.  But  besides  these,  there  are  several  of  the  vegetable  and 
animal  products  which,  when  applied  to  the  body,  produce  mus- 
cular contraction  by  an  agency  which  cannot  clearly  be  traced 
to  any  chemical  property  they  possess.  This  class  of  stimuli 
includes  a  variety  of  substances  which  are  denominated  acrid, 
and  others  which  are  called  narcotics,  because  when  largely 
applied  they  destroy  altogether  the  power  of  contraction,  and  soon 
extinguish  life.  As  an  example  of  this  latter  class,  we  may  take 
opium  and  hydrocyanic  acid. 

205.  Some  particular  muscles  have  a  disposition  to  be  acted  on 
more  especially  by  particular  kinds  of  stimuli.     Each  stimulus 


MUSCULAR    CONTRACTILITY.  107 

applied  to  the  body  generally,  appears  to  exert  a  particular  in- 
Huencc  upon  certain  parts  of  the  system  which  are  predisposed  to 
be  affected  by  it,  while  on  other  parts  it  appears  to  be  wholly  inert. 
Thus,  emetic  substances  act  principally  on  the  stomach,  even 
wdien  applied  to  a  diHcrent  part  of  the  system  ;  and  cathartic  sub- 
stances act  specifically  on  the  intestines.  The  muscular  fibres  of 
the  heart  are  more  particularly  excited  to  contraction  by  the  in- 
flux of  blood  into  the  cavities  of  that  organ ;  and  in  like  manner, 
every  system  of  muscular  fibres  concerned  in  carrying  on  the 
vital  functions  has  a  specific  disposition  to  be  affected  by  its 
appropriate  stimulus. 

206.  All  the  muscles  which  move  the  joints  of  the  limbs,  aiad 
the  several  parts  of  which  the  skeleton  is  composed,  together 
with  several  muscles  attached  to  the  softer  parts,  such  as  the 
eye,  tongue,  and  throat,  are  excited  to  contract  by  the  stimulus 
of  the  will,  and  are  therefore  called  voluntary  muscles.  They 
compose  a  class,  by  themselves,  as  distinguished  from^  those 
muscles  which  are  not  under  the  control  of  volition,  and  which 
are  therefore  involuntary  muscles,  such  as  the  heart,  stomach, 
intestines,  and  blood-vessels.  The  nature  of  this  distinction,  and 
of  the  different  laws  under  which  each  class  of  muscles  act,  will 
be  afterwards  pointed  out,  when  we  come  to  treat  of  the  physi- 
ology of  the  nervous  system, 

207.  The  natural  state  of  a  muscle,  or  that  in  which  it  exists 
when  not  acted  upon  by  any  external  cause,  is  relaxation.  When 
contracted,  its  surface,  from  being  smooth,  becomes  furrowed, 
its  middle  portion  swells  out,  and  grows  exceedingly  hard  and 
firm,  while  the  extremities  are  drawn  nearer  to  each  other,  so 
that  the  muscle  is  now  both  thicker  and  shorter  than  it  was  before. 

208.  It  has  been  frequently  made  a  question  whether  the 
increase  of  thickness  exactly  compensates  for  the  diminution  of 
length.  This  point  might  be  determined  by  ascertaining  whether 
the  specific  gravity  of  a  muscle  undergoes  any  alteration  during 
this  change.  Glisson  had  inferred  from  some  experiments  which 
he  had  made  on  this  subject,  that  the  bulk  of  a  muscle  is,  on  the 
whole,  diminished  when  it  is  in  a  state  of  contraction.  Sir  Gilbert 
Blane,*  on  the  contrary,  inferred  from  experiments  which  he 
made  on  fishes  confined  in  a  glass  vessel  with  a  very  slender 
neck,  that  the  absolute  bulk,  and  of  course  the  specific  gravity, 
of  their  muscles  remains  the  same  whether  they  are  contracted 
or  relaxed;  for  the  level  of  the  water  in  the  narrow  stem  of  the 
vessel  was  observed  to  be  unafl'ected  by  the  muscular  exertions 
made  by  the  fish.  Mr.  Mayo,  by  an  experiment  of  this  kind  on 
the  heart  of  a  dog,  found  the  bulk  of  that  organ  unchanged  during 
its  contraction  or  relaxation.f 

*  Phil.  Trans,  for  1805,  p.  22,  23. 

f  Anatomical  and  Physioligical  Comnnentaries,  p.  12.  [See,  on  the  whole 
of  this  subject,  DungUsoii' s  Fhysiolugy,  3d  edit.,  1.  341.] 


108  MECHANICAL    FUNCTIONS. 

209.  The  long- continued,  or  frequent  application  of  a  stimulus 
■to  a  muscle,  tends  to  impair  its  power  of  contracting,  or  in  other 
words,  to  exhaust  its  irritability.  This  liability  to  exhaustion  is 
exemplified  by  all  the  muscles  that  are  under  the  control  of  the 
will.  We  cannot  continue  to  exert  the  same  muscle,  or  set  of 
muscles  with  the  same  degree  of  power  beyond  a  certain  time, 
however  strong  may  be  the  motive  to  continue  that  action,  and 
whatever  mental  effort  we  may  make  to  persevere.  If,  for 
•example,  we  extend  the  arm  in  a  horizontal  hne,  with  a  weight 
held  in  the  hand,  we  shall  find,  in  the  course  of  a  few  minutes, 
that  the  sense  of  fatigue  becomes  intolerably  acute  ;  and  the  arm 
at  length  drops  from  mere  exhaustion,  in  spite  of  every  voluntary 
•eflfort. 

210.  The  contraction  of  a  muscle  ceasing  on  the  removal  of 
-the  stimulus  that  produced  it,  relaxation  succeeds,  and  the  muscle 
becomes  again  elongated ;  not,  however,  in  consequence  of  any 
inherent  power  of  elongation,  but  from  the  operation  of  causes 
which  are  extraneous  to  it.  The  elasticity  of  surrounding  parts 
is  often -sufficient  to  produce  this  effect;  but  in  most  cases  the 
elongation  of  the  relaxed  muscle  is  the  consequence  of  the  action 
of  other  muscles,  which  produce  motion  in  a  contrary  direction. 
Almost  every  muscle  has  another  corresponding  muscle,  or  set 
of  muscles,  which  are  antagonists  to  it.  If  the  one,  for  instance, 
binds  a  joint,  the  antagonist  muscle  unbinds  or  extends  it ;  and 
.by  this  action  must  elongate  the  former  muscle. 

211.  The  swelling  of  the  muscles  of  the  limbs,  when  they  are 
in  strong  action,  is  matter  of  familiar  observation.  It  is  this  cir- 
cumstance, above  all  others,  which  renders  a  knowledge  of  ana- 
tomy so  essentially  necessary  to  the  painter  and  the  sculptor.  In 
•every  attitude  and  in  every  movement  of  the  body  some  particular 
set  of  muscles  are  in  action,  and  consequently  swelled  and  pro- 
minent, while  others  are  relaxed  and  less  conspicuous ;  and  unless 
these  differences  were  accurately  noted  and  faithfully  expressed, 
it  would  be  impossible  to  give  a  correct  representation  of  the 
living  figure. 

212.  Although  the  fibres  which  compose  the  smaller  portions 
of  a  muscle  are  arranged  in  parallel  directions,  yet  the  disposition 
of  the  mass  of  fibres,  relatively  to  the  whole  muscle,  varies  con- 
siderably according  to  the  action  which  the  muscle  is  intended  to 
perform.  We  find  them,  in  some  cases,  radiating  from,  or  con- 
verging to  a  particular  point;  and  sometimes  we  even  find  that 
the  different  portions  of  a  muscle  having  this  structure  can  act 
independently  of  the  rest.  The  temporal  muscle  is  an  instance 
of  a  muscle  of  which  the  fibres  converge  from  the  circumference 
to  a  central  point,  where  they  are  inserted  into  the  coronoid  pro- 
cess of  the  lower  jaw.  In  other  cases,  the  fibres  composing  the 
muscle  pass  in  a  circular  direction  so  as  to  close  upon  some  organ 


MUSCULAR    CONTRACTILITY.  109 

which  they  surround,  or  to  compress  the  bodies  they  enclose. 
Thus  the  eye  and  the  mouth  are  closed  each  by  a  circular  or 
orbicular  muscle.  In  other  parts,  muscles  of  this  description  are 
called  sjMncters.  Some  parts,  as  the  iris,  are  provided  with  both 
radiating  and  circular  fibres,  the  one  used  for  dilating,  and  the 
other  for  contracting  the  central  aperture.  We  meet  with  a 
circular  arrangement  of  muscular  fibres  in  the  coats  of  the  various 
pipes  and  canals  of  the  body,  such  as  the  blood-vessels  generally, 
and  also  the  alimentary  passages;  and  together  with  these  cir- 
cular fibres  are  also  often  found  bands  of  longitudinal  fibres, 
which  shorten  the  tube,  while  the  former  tends  to  contract  its 
diameter,  and  press  upon  its  contents.  The  several  hollow  re- 
ceptacles for  fluids,  such  as  the  heart  and  the  stomach,  present 
us  with  a  still  greater  complication  in  the  arrangement  of  their 
muscular  fibres,  in  which  we  may  sometimes  trace  layers  of  fibres 
having  a  spiral  course. 

213.  But  it  very  frequently  happens  that  the  action  of  a  muscle 
is  wanted  when  its  presence  would  be  exceedingly  inconvenient. 
The  common  medium  of  connexion  employed  by  mechanicians, 
when  the  object  to  be  moved  is  at  too  great  a  distance  to  admit 
of  the  direct  application  of  the  power,  is  that  of  a  rope  or  strap. 
In  the  animal  machine  the  same  purpose  is  effected  by  means  of 
tendons,  which  are  Ions;  strings  attached  at  one  end  to  the  mus- 
cle,  and  at  the  other  to  the  bone,  or  part  to  be  moved.  If  the 
muscles  by  which  the  fingers  are  bent  and  extended,  for  instance, 
had  been  placed  in  the  palm  or  back  of  the  hand,  they  would  have 
enlarged  that  part  to  an  awkward  and  clumsy  thickness,  which 
would  not  only  have  destroyed  the  beauty  and  proportion  of  the 
organ,  but  have  impeded  many  of  its  uses  as  an  instrument. 
They  are  therefore  disposed  at  the  arm,  even  as  high  up  as  the 
elbow,  and  their  tendons  pass  along  the  joints  of  the  wrist,  to  be 
affixed  to  the  joints  of  the  fingers  they  are  intended  to  move. 

214.  The  employment  of  tendons  also  reduces  the  space  which 
would  have  been  necessary  for  the  direct  insertion  of  the  muscu- 
lar fibres  into  a  bone,  so  that  the  same  bone  may  be  acted  upon 
in  a  great  variety  of  ways,  by  means  of  the  tendons  attached  to 
it  proceeding  from  a  great  number  of  muscles. 

215.  Another  advantage  resulting  from  the  employment  of 
tendons  is,  that  by  their  intervention  a  great  number  of  fibres  are 
made  to  act  in  concert,  and  their  united  power  is  concentrated 
upon  one  particular  point.  In  this  respect,  also,  they  resemble  a 
rope,  at  which  a  great  number  of  men  are  pulling  at  the  same 
moment,  by  which  means  their  combined  strength  is  brought  into 
action.  These  tendons  are  variously  disposed  with  respect  to 
the  muscular  fibres  to  which  they  are  attached.  It  is  but  in  a 
few  muscles  that  the  fibres  are  arranged  in  a  perfect  longitudinal 

10 


110  MECHANICAL    FUNCTIONS. 

direction.  We  often  find  them  covered  on  both  sides  with  a  ten- 
dinous investment,  the  muscular  fibres  proceeding  obliquely  from 
the  one  to  the  other.  This  arrangement  forms  what  is  called  a 
penniform  muscle,  which  may  be  either  single  or  double.  The 
structure  is  frequently  even  more  complex  than  this,  a  number 
of  tendinous  layers  being  interposed  among  the  fleshy  fibres.  By 
means  of  tendons  a  different  direction  may  also  be  given  to  the 
moving  power,  without  altering  its  position.  There  are  many 
instances  of  this  employment  of  tendons,  in  which  they  are  made 
to  pass  through  a  loop,  which  serves  as  a  pulley,  an  expedient 
which  is  adopted  in  one  of  the  oblique  muscles  of  the  eye. 

216.  We  have  already  seen,  that  wherever  friction  takes 
place  by  the  motion  of  tendons  over  bones,  or  other  hard  parts, 
a  bursa  mucosa  is  interposed,  which  obviates  in  a  great  measure 
the  injurious  effects  that  would  otherwise  result  from  the  rubbing 
of  the  parts. 

217.  But  although  it  be  true  that  the  force  with  which  mus- 
cles contract  is  very  great,  yet  the  extent  to  which  they  are 
capable  of  exerting  that  force  is  in  general  very  limited,  and 
would  be  insufficient  for  most  of  the  purposes  their  contraction 
is  intended  to  serve,  unless  it  were  very  considerably  enlarged 
by  mechanical  expedients.  In  the  practice  of  mechanics  we 
find  a  variety  of  contrivances  had  recourse  to  for  attaining  this 
object;  namely,  the  production  of  a  great  extent  of  motion,  by 
a  power  acting  through  very  limited  space.  But  most  of  these 
devices  would  not  answer  in  the  human  body,  from  the  incon- 
venience which  would  attend  their  application.  We  find  that 
nature  has  solved  this  problem  in  the  simplest  possible  manner. 
In  the  first  place,  the  tendons  are  inserted,  into  the  bones  they 
are  designed  to  move,  very  near  to  the  centres  of  motion,  so 
that  a  small  extent  of  contraction  in  the  muscle  will  produce  a 
great  range  of  motion  at  the  other  extremity  of  the  limb.  The 
principle  is  here  obviously  that  of  what  mechanicians  have 
termed  a  lever  of  the  third  class,  namely,  that  in  which  the 
power  is  applied  at  some  point  intermediate  between  the  fulcrum 
and  the  weight  to  be  raised,  or  resistance  to  be  overcome. 
Secondly,  the  direction  of  the  power  so  applied,  with  reference  to 
the  line  connecting  the  point  of  application  and  the  centre  of 
motion,  or  what  is  termed  the  radius  of  rotation,  is  oblique ;  that 
is,  it  forms  with  it  an  acute  angle.  Here  again  we  may  perceive 
another  cause  of  the  increase  of  motion,  obtained  by  a  smaller 
extent  of  contraction  above  that  which  would  have  resulted  if 
the  power  had  been  applied  at  right  angles  to  the  radius  of  rota- 
tion, which  is  obviously  the  most  advantageous  mode  of  employ- 
ing that  power,  when  the  object  is  to  economise  it,  by  giving  it 
the  greatest  mechanical  advantage.     It  must  happen,  indeed,  by 


MUSCULAR    CONTRACTILITY.  Ill 

such  a  disposition  of  the  force,  that  a  large  portion  of  it  is  lost, 
being  spent  on  a  fixed  obstacle,  namely,  on  the  bone  of  the  joint, 
against  which  the  pressure  is  exerted  ;  but  the  quickness  and 
velocity  of  the  motion  that  results  are  undoubtedly  increased. 
Thirdly,  the  muscular  fibres  are  theiioselves  obliquely  disposed 
with  respect  to  the  tendons,  so  that  the  same  cause  operates  in  a 
similar  manner  here  also.  Lastly,  pairs  of  muscles  are  placed 
so  as  to  form  an  obtuse  angle  with  one  another,  and  are  made  to 
contract  at  the  same  time.  Their  actions,  therefore,  will  partly 
concur,  and  partly  oppose  one  another.  They  will  conspire  to 
produce  a  movement  in  the  parts  to  which  their  extremities  are 
attached,  in  a  direction  intermediate  to  that  of  the  muscles  them- 
selves ;  for  it  is  a  fundamental  law  of  dynamics,  that  when  a 
body  is  urged  by  two  forces  inclined  to  each  other  at  any  angle, 
it  will  move  as  if  it  were  ura-ed  bv  a  force  in  the  direction  of  the 
diagonal  of  a  parallelogram,  having  for  its  sides  lines  corres- 
ponding in  their  direction  and  their  lengths  to  the  directions  and 
relative  intensities  of  the  two  component  forces. 

218.  In  all  these  cases  it  is^  evident  that  there  must  be  a  great 
loss  of  force  ;  but  when  the  muscular  power  is  concerned,  we 
almost  always  find  that  strength  is  sacrificed  to  convenience,  and 
that  construction  adopted  which  unites  on  the  whole  the  most 
advantages.  We  must  allow,  that  the  muscular  power  is  turned 
to  the  best  account  when  it  is  made  to  perform  in  the  completest 
and  quickest  manner  the  intended  motion.  We  find,  in  following 
the  mechanism  not  only  of  the  joints  of  the  limbs,  but  of  the 
whole  system  of  organs,  both  internal  and  external,  that  the  mode 
in  which  this  force  is  applied  is  diversified  in  every  possible  way. 
Its  combinations  are  varied,  and  its  action  modified  beyond  calcu- 
lation, though  the  original  power  be  still  essentially  the  same, 
and  observe  the  same  laws  in  its  action. 

219.  The  source  of  that  enormous  mechanical  power,  which 
seems  to  be  an  inherent  property  of  the  muscular  power,  has 
long  been  sought  for  by  physiologists ;  but  it  has  always  conti- 
nued to  elude  their  most  patient  and  laborious  researches.  It 
was  at  one  periqd  a  favourite  subject  of  speculation  to  devise 
hypotheses  as  to  mechanical  arrangements  of  particles  capable 
of  producing  results  similar  to  those  of  muscular  contraction. 
Borelli*  conceived  that  each  muscular  fibre  might  be  composed 
of  a  series  of  minute  bladders,  or  vesicles,  of  a  rhomboidal  figure. 
Stuart  supposed  that  these  vesicles  were  I'ound.  But,  on  either 
hypothesis  they  were  conceived  to  be  empty  while  the  muscle 
remained  in  its  natural  state  of  relaxation.  On  the  sudden  intro- 
duction of  a  fluid  of  some  kind  into  these  vesicles,  their  sides 
would  be  separated,  they  would  become  distended,  and,  assuming 

*  De  Motu  Anirnalium, 


112  MECHANICAL    FUNCTIONS. 

a  more  spherical  form,  would  consequently  be  shortened  in  their 
longitudinal  diameter ;  and  as  this  shortening  would  take  place 
simultaneously  in  all  the  vesicles,  the  whole  muscle  would  be 
contracted  in  its  length,  and  at  .the  same  time  proportionally 
dilated  in  its  breadth.  The  contrivance  had  certainly  the  merit 
of  ingenuity,  inasmuch  as  it  explained  the  swelling  of  the  muscle 
as  well  as  its  shortening,  in  the  act  of  contraction.  But  it  evi- 
dently will  not  bear  the  test  of  serious  examination.  No  such 
structure  as  is  implied  in  the  hypothesis  has  ever  been  rendered 
visible  to  the  eye,  however  dexterously  the  microscope  may  have 
been  applied  to  the  muscular  fibre  ;  nor  can  we  find  any  power 
sufficient  to  propel  so  large  a  quantity  of  fluid  as  would  be  re- 
quired for  the  distension  of  the  vesicles  ;  an  effect  also  which,  in 
order  that  the  theory  may  correspond  wdth  the  phenomena,  must 
be  produced  almost  instantaneously.  The  resistance  that  would 
be  opposed  to  the  entry  of  a  fluid  so  propelled  would  be  incalcu- 
lable, and  incomparably  greater  than  that  exerted  by  the  muscle 
itself,  which  latter  force,  it  may  be  observed,  it  is  the  professed 
object  of  this  theory  to  explain.  The  hypothesis  itself,  therefore, 
on  which  the  theory  is  built,  involves  a  greater  difficulty  than 
the  simple  fact.  Such,  indeed,  was  a  very  common  mistake  in 
the  speculations  of  the  earlier  philosophers,  who  were  ever  prone 
to  theorize  without  having  any  legitimate  basis  for  the  formation 
of  a  theory  ;  their  foundations  being  often  more  in  need  of  sup- 
port than  the  superstructure  they  attempted  to  raise  upon  it.  It 
I'erainds  us  of  the  Indian  fable  of  the  world  being  carried  on  the 
back  of  an  elephant,  whilst  the  elephant  was  supposed  to  require 
a  tortoise  for  its  own  support. 

220.  The  hypothesis  that  the  fibres  of  muscles  have  a  spiral 
shape,  and  pass  in  a  contorted  line  from  one  end  of  the  muscle 
to  the  other,  like  the  turns  of  a  corkscrew,  a  form  which  readily 
admits  of  elongation  or  contraction,  according  as  it  is  more  or  less 
contorted,  is  quite  as  unsatisfactory  as  the  former;  and  equally 
open  to  the  fundamental  objection,  that  it  leaves  the  original 
source  of  motion  still  unexplained.  Muscular  power,  indeed, 
does  not  appear,  from  what  we  hitherto  know  of  its  laws,  to  bear 
any  close  analogy  to  any  of  the  other  great  principles  in  nature, 
which  we  recognize  as  original  sources  of  mechanic  force ;  and 
until  such  analogy  can  be  traced,  all  our  gndeavours  to  explain 
the  phenom.ena  of  muscular  contraction  must  be  fruitless. 

221.  It  was  a  favourite  notion  with  the  physiologists  of  the 
seventeenth  century,  that  an  eflfervescence  was  excited  in  the 
interior  of  the  muscle,  by  some  chemical  operation  ;  such  as  a 
mixture  of  acid  and  alkali.  Willis  and  others  ascribed  muscular 
contraction  to  a  fermentation  occasioned  by  the  union  of  the 
particles  of  the  muscle,  with  a  supposed  nervous  fluid,  or  ethereal 
spirit  contained  in  the  blood. 


MUSCULAR    CONTRACTILITY-  113 

222.  But  in  fact,  the  only  power  in  nature  to  which  irritability 
can  be  compared  in  the  quickness  and  suddenness  of  its  variations, 
as  well  as  in  its  dependence  on  peculiar  qualities  of  matter,  is 
electricity,  and  more  particularly  that  form  of  electricity  which 
constitutes  galvanism.  Attempts  have  accordingly  been  often 
made,  since  the  phenomena  of  galvanism  have  engaged  so  much 
attention  in  the  philosophic  world,  to  explain  muscular  contrac- 
tion by  means  of  this  principle  ;  and  endless  have  been  the  fanciful 
hypotheses  invented  for  this  purpose.  Each  muscular  fibre  was 
at  one  time  considered  as  performing  the  office  of  a  separate 
Leyden  jar,  charged  with  opposite  electricities  on  its  exterior  and 
interior ;  whilst  the  filament  of  nerve  which  penetrated  into  its 
substance  was  the  conducting  wire,  that  occasioned  the  discharge 
of  the  jar.  After  the  discovery  of  the  voltaic  pile,  it  was  im- 
mediately conceived  that  an  arrangement  corresponding  to  the 
plates  of  the  pile,  existed  among  the  particles  of  nerve  and  muscle, 
thus  composing  a  galvanic  apparatus,  ready  to  discharge  itself 
when  the  proper  communications  were  affected.  The  latest 
hypothesis  of  this  kind,  is  that  of  Prevost  and  Dumas,  who  con- 
ceived that  the  muscular  fibre  was  thrown,  during  its  contraction, 
into  serpentine  flexures,  in  consequence  of  the  attractions  of 
electrical  currents,  passing  in  similar  directions  through  minute 
filaments  of  nerves,*  the  directions  of  which  were  at  right  angles 
to  the  axis  of  the  fibres.  But  in  the  present  state  of  the  science, 
all  these  analogies  are  far  too  vague  and-  remote  to  serve  as  the. 
foundation  of  any  solid  theory .f 

223.  It  has  been  the  fashion  among  some  physiologists  to  con- 
sider muscular  contraction  as  only  a  particular  mode  of  attrac- 
tion, and  as  included  in  the  general  law  of  attraction  which 
subsists  among  all  the  particles  of  matter;  but  this  is  a  generali- 
zation totally  unwarranted  by  the  phenomena.  Others  have 
maintained  that  contractility  is  to  be  ascribed  to  the  attraction 
of  life,  and  to  be  merely  a  modification  of  vitality.     Thus,  Gir- 

*  [Dr.  Rog-et,  himself,  was  at  one  time  disposed  to  think,  that  light  might 
be  thrown  upon  the  subject  of  muscular  contraction  by  investigations  of  this 
nature.  A  slender  harpsichord  wire,  bent  into  a  helix,  being  placed  in  a  vol- 
taic circuit,  instantly  shortened  itself  whenever  the  electric  stream  was  sent 
through  it,  but  recovered  its  former  dimensions  the  moment  the  current  was 
intermitted.  (Electro-Magnetism,  p.  59,  in  Vol.  11.  of  Natural  Philosophy, 
Library  of  Useful  Knowledge,  Lond.  1832.)  From  this  experiment,  the 
author  presumed,  that  possibly  some  analogy  might  hereafter  he  found  to  exist 
between  this  phenomenon  and  the  contraction  of  muscular  fibres.  From  his 
silence,  however,  in  the  text,  Tt  would  appear,  that  farther  reflection  had  not 
confirmed  the  suggestion. 

A  striking  objection  to  all  these  hypotheses  is, — that  the  irritability  of 
the  muscle  is  lost  sight  of,  and  the  nerve  alone  regarded  to  be  active ;  whereas, 
the  nervous  power  appears  to  act  merely  as  an  excitant — like  galvanism — to 
the  irritability,  and — as  experiments  show — exhausts  it  like  any  other  ex- 
citant.] 

10* 


114  MECHANICAL    TUNCTIONS. 

tanner  imagined  that  this  property  resided  even  in  the  living 
fluids,  and  was  co-extensive  with  organized  nature.  This,  how- 
ever, is  equivalent  to  the  assertion,  that  the  phenomena  requires 
no  explanation  at  all ;  for  it  certainly  leaves  the  question  just 
where  it  was  before.  We  already  knew  that  the  effects  of 
muscular  power  indicated  a  peculiarity  in  the  nature  of  that 
power,  for  they  appeared  diflerent  from  any  other.  To  say  that 
it  is  a  peculiar  modification  of  the  power  of  life,  gives  us  there- 
fore no  new  information,  unless  it  be  meant  that  it  is  similar  in 
its  nature  to  the  powers  which  the  living  organs  exhibit;  but  it 
would,  in  that  case,  convey  an  erroneous  idea,  because,  the  phe- 
nomena themselves  being  different,  cannot,  according  to  the  rules 
of  legitimate  induction,  be  ascribed  to  the  same  physical  cause. 
We  have  already  pointed  out  the  fallacy  of  this  mode  of  reason- 
ing, in  which  final  causes  are  confounded  with  physical  causes, 
and  substituted  for  them  as  philosophical  explanations  of  phe- 
nomena. 

224.  There  is,  unquestionably,  a  greater  degree  of  cohesion  in 
the  particles  which  compose  the  fibres  of  muscles  in  their  living, 
than  in  their  dead  state.  This  cohesive  power,  in  consequence 
of  the  connexions  of  the  muscle  in  the  body,  is  equivalent  to  a 
constant  tendency  to  contraction.  Hence,  the  fibres  of  muscles 
are  in  a  constant  state  of  tension,  like  an  elastic  substance  kept 
upon  the  stretch.  This  property,  evidently  derived  from,  con- 
tractility, has  been  denominated  tonicity,  a  term  which  has  also, 
as  we  have  seen,  been  applied  to  the  peculiar  state  of  tension  of 
cellular  and  membranous  structures,  derived  from  a  particular 
condition  of  their  elasticity.  (See  §  175.)  It  produces  the  state 
of  tone  in  a  muscle ;  or  that  in  which  it  is  disposed  to  contract  a 
greater  degree,  than  its  connexions  with  the  neighbouring  parts 
will  allow.  This  explains  why,  on  cutting  a  muscle  across,  the 
cut  edges  retract  to  a  considerable  extent,  leaving  a  wide  gap  at 
the  place  of  section:  when,  by  a  sudden  effort,  the  tendo-achilles 
is  ruptured,  the  muscles  in  the  calf  of  the  leg  to  which  that  tendon 
had  been  attached,  being  released  from  this  stretching  force, 
retract  to  a  great  extent,  and  form  a  large  and  hard  swelling  high 
up  in  the  leg. 

225.  On  minutely  examining  the  phenomena  of  muscular  con- 
traction, it  will  be  found,  even  in  those  instances  in  which  the 
contractile  power  appears  to  be  exerted  with  undiminished 
vigour  for  a  certain  time,  that  each  individual  fibre  undergoes, 
during  the  interval,  a  succession  of  changes  of  condition,  con- 
tracting and  relaxing  alternately.  It  is  only  a  certain  number  of 
the  fibres  that  are  in  action  at  the  same  moment;  their  power  is 
soon  exhausted ;  and  until  recruited  by  repose,  other  sets  of  fibres 
are  thrown  into  contraction,  so  as  to  supply  their  place.  They 
thus  relieve  one  another  in  succession,  until  by  frequent  action 


FUNCTIONS    OP    THE    OSSEOUS    FABRIC.  115 

the  exhaustion  becomes  more  general,  and  the  restoration  less 
complete.  In  this  state,  the  whole  muscle  is  fatigued,  its  con- 
tractions become  irregular  and  unsteady  in  proportion  as  they 
are  more  feeble,  and  the  whole  action  is  tremulous,  and  incom- 
petent to  the  production  of  the  desired  effect.  These  tremulous 
movements  are  very  obvious  when  the  muscles  are  weakened 
from  any  cause,  as  well  as  when  exhausted  by  excessive  action. 
Dr.  Woilaston,*  with  his  usual  acuteness,  detected,  by  a  very 
simple  experiment,  the  minute  oscillations  consequent  upon  these 
continual  and  rapid  alternations  of  contraction  and  relaxation  in 
the  fibre.  When  the  finger  is  inserted  in  the  ear  with  a  moderate 
degree  of  force,  and  the  pressure  is  continued  with  as  much 
steadiness  as  possible,  a  peculiar  vibratory  sound  is  heard,  similar 
to  that  of  a  carriage  rolling  on  the  pavement.  This  must  evi- 
dently proceed  from  a  corresponding  vibratory  action  of  the 
muscular  fibres.  It  appears,  therefore,  as  Dr.  Woilaston  remarks, 
that  the  voluntary  effect  in  this  case,  although  it  may  seem  to  us 
to  be  perfectly  continuous,  consists  in  reality,  of  a  great  number 
of  vibrations  repeated  at  extremely  short  intervals. 

226.  There  is  a  peculiar  kind  of  contractility  possessed  by 
membranous  structures,  v^^hich  has  often  been  supposed  to  bear 
an  analogy  to  muscular  contractility,  or  even  to  be  some  modi- 
fication of  this  property.  It  is  called  into  action  by  the  applica- 
tion of  a  certain  degree  of  heat,  and  also  by  some  powerful 
chemical  agent,  such  as  the  concentrated  mineral  acids;  and  the 
effect  produced  is  a  sudden  corrugation,  or  curling  up  of  the 
membranous  part.  This  phenomenon  was  noticed  by  Haller, 
and  was  termed  by  Bichat  racornissement.  Alcohol,  and  many 
of  the  neutral  salts  produce,  but  more  slowly,  effects  which  are 
similar  in  kind,  though  much  inferior  in  degree;  but  in  this  case 
the  corrugation  continues  to  increase,  if  the  agent  continues  ap- 
plied, which  does  not  happen  when  the  more  powerful  agents,  as 
the  acids  or  boiling  water,  are  employed;  for  the  continued 
operation  of  these  latter  agents  is  to  dissolve  and  disorganize  the 
animal  substance.  Bichat  took  considerable  pains  to  investigate 
these  phenomena,  and  has  pointed  outf  several  circumstances  by 
which  this  property  may  be  distinguished  from  mere  membra- 
nous elasticity.  From  muscular  contractility,  indeed,  it  differs 
much  more  considerably,  and  depends,  therefore,  in  all  proba- 
bility,  on  principles  totally  different  from  that  remarkable  animal 
property. 

Sect.  V. — Functions  of  the  Osseous  Fabric  or  Slieleton. 

227.  The  general  basis  for  the  mechanical  support  of  all  the 
softer  organs  of  the  body,  both  in  their  states  of  quiescence  and 

*  Philosophical  Transactions  for  1810,  p.  3. 
f  Anatomie  Generale. 


116  MECHANICAL,    FUNCTIONS. 

of  motion,  is  the  osseous  fabric,  or  skeleton ;  composing  a  con- 
nected frame-work  of  solid  and  unyielding  structures,  fitted  for 
the  threefold  purposes  of  giving  protection  to  the  more  im- 
portant organs  which  perform  the  vital  functions,  of  sustaining 
the  weight  of  the  several  portions  into  which  the  body  may  be 
conceived  to  be  divided,  and  of  furnishing  fixed  points  of  attach- 
ment to  the  muscles  or  moving  powers,  and  thus  supplying  them 
with  the  mechanical  advantages  of  levers  in  the  execution  of  the 
more  powerful  movements  of  the  frame,  and  especially  in  the 
progressive  motion  of  the  whole  body  from  place  to  place. 

228.  The  organs,  more  especially  defended  from  external 
injury  by  a  bony  covering,  are  the  brain,  the  principal  organs  of 
the  senses,  and  the  organs  of  circulation  and  respiration. 

1.   The  Cranium. 

229.  The  bones  of  the°lskull  are  contrived  with  singular  artifice 
and  skill  to  afford  protection  to  the  brain,  an  organ,  as  we  have 
seen,  of  peculiarly  soft  and  delicate  texture,  and  of  which  the 
functions  are  so  refined  as  to  require  for  their  accomplishment 
the  most  perfect  freedom  from  external  pressure,  and  even  from 
any  harsh  vibration  or  concussion  of  its  parts.  It  is  evidently 
with  this  view,  that  the  bony  covering  of  th^  brain,  or  skull-cap, 
as  it  has  been  called,  is  constructed  in  the  form  of  a  vault  or' 
dome,  as  being  the  best  calculated  to  resist  external  pressure,  on 
the  well-known  mechanical  principle  of  the  arch.  But  pressure 
applied  vertically  to  an  arch  necessarily  gives  rise  to  an  outward 
horizontal  thrust  at  the  two  ends  of  the  arch.  In  architecture, 
various  expedients  are  resorted  to  for  opposing  this  force.  In  a 
bridge  it  is  resisted  by  the  solid  abuttnents  where  the  arch  takes 
its  rise  on  each  side.  In  the  higher  arches  of  ornamental  archi-  ' 
lecture  it  is  counteracted  by  the  weight  of  a  buttress  placed  over 
the  origin  of  the  arch,  and  in  harmony  with  the  design  of  the 
whole.  For  the  support  of  the  roof  of  a  building,  which  has  to 
rest  upon  perpendicular  walls,  either  these  walls  must  be  built 
of  a  strength  equal  to  withstand  this  horizontal  pressure,  or, 
what  is  generally  resorted  to,  a  tie-beam  must  be  attached  to 
the  base  of  the  roof,  which  tie-beam  will  resist  by  its  cohesive 
strength  the  force  which  tends  to  stretch  it,  derived  from  the 
outward  pressure  of  the  roof 

230.  In  the  architecture  of  the  skull  we  find  the  exemplifica- 
tion of  these  methods,  and  their  strict  conformity  with  the  refined 
principles  of  mechanics.  The  two  parietal  bones  on  the  sides, 
the  frontal  bone  before,  and  the  occipital  bone  behind,  may  be 
considered  as  the  four  great  stones  which  compose  the  convex 
part  of  the  dome.  If  we  first  consider  the  parietal  bones,  view- 
ing them  as  constituting  a  single  arch,  we  find  that  their  lower 


'  FUNCTIONS    OP    THE    OSSEOUS    FABRIC.  117 

edges  are  bevelled  off  at  an  acute  angle,  so  as  to  be  overlapped 
on  each  side  by  the  upper  edge  of  the  tennporal  bone,  which  con- 
tinues the  curvature  as  far  as  the  basis  of  the  skull.  Thus,  the 
two  parietal  bones  are  effectually  wedged  in  between  the  two 
temporal  bones,  and  any  pressure  applied  on  the  top  of  the  head, 
which  would  of  course  tend  to  thrust  their  lower  sides  outwards, 
is  resisted  by  the  temporal  bones.  But  these  lemporal  bones  are 
themselves  locked  into  the  irregularly-shaped  sphenoidal  bone, 
which,  as  we  have  seen,  forms  the  central  piece  of  the  basis  of 
the  skull,  being  in  actual  contact  with  every  one  of  the  bones 
which  compose  it,  as  well  as  the  face,  in  which  the  organs  of  all 
the  senses,  except  that  of  touch,  is  contained.  The  os  sphenoides 
thus  performs  the  office  of  a  great  tie-beam  to  the  lower  part  of 
the  arched  roof  of  the  skull :  and  the  same  principles  will  be  found 
to  hold  gpod  when  the  section  of  the  skull  is  taken  in  the  longi- 
tudinal direction ;  the  os  frontis  before,  and  the  os  occipitis  behind, 
which  sustain  their  share  of  any  pressure  made  on  the  upper 
parts  of  the  head,  being  so  locked  in,  by  the  bending  inwards  of 
their  lower  processes,  with  the  sphenoid  bone,  as  effectually  to 
prevent  their  starting  outwardly. 

231.  Another  circumstance  in  the  architecture  of  the  skull  is 
particularly  deserving  of  notice,  as  it  exhibits  the  most  marked 
instance  of  provident  design.  It  relates  to  the  structure  of  the 
bones  themselves,  which  is  the  best  calculated  to  resist  fracture 
on  the  one  hand,  and  on  the  other  to  prevent  the  transmission  of 
vibrating  concussions  to  the  brain.  It  is  manifestly  with  this 
view  that  it  is  composed  of  two  plates  of  bone,  the  external  one 
fibrous,  tough,  and  not  easily  broken ;  the  inner  one  more  dense 
and  rigid,  offering  the  most  powerful  resistance  to  simple  direct 
pressure ;  yet,  on  that  very  account,  more  fragile  in  its  nature, 
and  partaking  therefore  in  the  quality  of  brittleness,  which  belongs 
to  all  the  harder  bodies,  such  as  glass  or  flint.  It  was  on  account 
of  its  possessing  this  property  that  it  was  named  the  tabula 
vitrea  by  anatomists.  But  while  it  is  evident  that  such  an  acci- 
dent would  have  been  of  frequent  occurrence  if  that  part  of  the 
bone  had  been  directly  exposed  to  every  casual  blow,  this  ^vil 
has  been  carefully  guarded  against  by  the  interposition  of  a 
spongy  intertexture  of  bon\^  fibres,  the  canceUaied  stnccture,  as 
it  is  termed,  which  forms  a  thick  layer  between  the  two  laminas 
of  bone,  or  as  they  have  been  called,  the  outer  and  the  inner 
tables  of  the  skull.  This  intervening  layer  operates  as  a  cushion, 
arresting  the  progress  of  the  vibrations  from  the  external  to  the 
internal  plate  of  bone,  and  preventing  fracture. 

232.  Even  when  the  impetus  is  so  great  as  to  penetrate 
through  this  resisting  medium,  still  the  force  with  which  it  im- 
pinges on  the  subjacent  parts  must  be  very  considerably  mode- 
rated, and  the  danger  of  injury  to  the  brain  diminished.     It  is 


118  MECHANICAL    FUNCTIONS. 

witFi  a  similar  design  of  giving  protection  that  a  soldier's  helmet 
is  lined  with  leather  or  covered  with  hair  ;  a  provision  which  we 
even  find  in  the  head-piece  of  the  Roman  soldiers,  in  whose 
equipment  utility  alone  was  consulted,  and  nothing  was  admitted 
that  served  the  purpose  of  mere  ornament.  Wherever  the  bones 
of  the  skull  are  more  particularly  exposed  to  blows,  we  find  a 
greater  thickness  of  bone  provided  for  the  sake  of  additional 
power  of  resistance. 

233,  The  sutures,  or  joinings  of  these  bones,  are  also  admirably 
contrived  to  stop  the  transmission  of  vibrations,  arising  from  per- 
cussion from  extending  to  any  distance  round  the  skull.  These 
sutures,  externally,  where  the  tough  and  fibrous  plates  of  bone 
are  united,  present  a  serrated  line ;  the  fibres  at  the  edges  of 
each  being  mutually  inserted  between  those  of  the  contiguous 
bone.  But  this  dove-tailed  joining  is  not  met  with  in  the  inner 
table ;  there  the  edges  of  the  bone  are  smooth  and  placed  in 
simple  contact.  This  is  evidently  done  in  order  to  prevent  the 
chipping  off  of  the  minute  parts  of  a  brittle  structure,  had  they  been 
interlaced  together  as  the  fibres  of  the  outer  table  are.  But  still 
the  interruptions  afforded  by  the  suture  tend  in  a  great  degree  to 
check  the  progress  of  fracture.* 

2.   The  Face. 

234.  The  organs  of  the  principal  senses,  the  eye,  the  ear,  the 
nostrils,  and  the  mouth,  are  protected  by  the  bones  of  the  face, 
which  likewise  form  part  of  the  skull.  The  eyes  are  exceedingly 
well  defended  by  the  superciliary  ridge  of  the  frontal  bone  above, 
and  also  by  the  orbital  plate  which  supports  the  anterior  lobes  of 
the  brain  ;  anteriorly,  they  are  protected  by  the  projection  of  the 
nasal  bones,  and  outwardly  by  the  arched  process  which  divides 
them  from  the  temples ;  while  the  prominent  cheek  bones  below 
guard  them  from  injury  in  that  quarter.  No  part  of  the  body 
has  so  effectual  a  protection  from  bone  as  the  internal  organ  of 
hearing :  nor  is  there  any  part  of  the  osseous  system  so  hard  as 
the  portion  of  the  temporal  bone  in  which  this  organ  is  lodged. 
The  nasal  cavities,  in  like  manner,  which  are  occupied  by  the 
membranes  receiving  impressions  from  odorous  effluvia,  are 
formed  in  deep  recesses  of  bone.  The  organ  of  taste  is  also  pro- 
tected by  the  jaws,  though  less  completely,  because  the  same 
parts  are  required  to  enjoy  extensive  power  of  motion. 

*  [This  is  questionable.  Observation  has  shown,  that  the  sutures  do  not 
possess  much,  if  any,  effect  in  puttingr  a  limit  to  fractures.  In  all  cases  of 
severe  blows,  the  skull  appears  to  resist,  as  if  it  were  constituted  of  but  one 
piece.] 


FUNCTIONS    OP    THE    OSSEOUS    FABRIC.  119 

3.  The  Thorax. 

235.  The  heart  and  lungs,  -which  are  lodged  in  the  cavity  of 
the  thorax,  are  defended  before  and  behind  by  the  spine  and 
sternum ;  and  laterally  by  the  ribs,  which  form  bony  arches,  the 
shape  best  calculated  for  resisting  pressure  applied  externally. 
They  are  formed  of  separate  pieces,  with  intervals  between,  in 
oi-der  to  admit  of  motion :  for  the  cavity  of  the  chest  requires  to 
be  alternately  enlarged  and  contracted  in  the  performance  of 
respiration,  which  is  a  function  of  primary  importance  in  the 
animal  economy. 

4.  The  Spine. 

236.  The  support  of  the  trunk  and  upper  parts  of  the  body, 
including  the  head,  is  entrusted  to  a  column  of  bones,  the  assem- 
blage of  which  constitutes  the  spine.  The  spine  is  that  part  of 
the  skeleton  of  all  animals  composing  the  four  superior  classes, 
namely,  the  mammalia,  birds,  fishes,  and  reptiles,  which  is  most 
constantly  found,  and  which  exhibits  the  greatest  uniformity  of 
structure.  The  individual  bones  which  compose  the  spine  are  so 
intimately  united  and  so  firmly  secured  by  ligaments  on  every 
side,  that  they  appear  in  the  living  body  as  one  continued  bone, 
and  the  whole  assemblage  is  known,  in  ordinary  language,  by 
the  name  of  the  hack-hone.  The  purposes  answered  by  this 
complex  fabric  are  numerous  and  important.  It  is  the  great 
central  beam  of  the  fabric,  and  furnishes  the  basis  of  support  to 
all  other  bones  of  the  skeleton.  It  serves,  in  particular,  to  unite 
the  bones  of  the  limbs  with  the  trunk,  so  that  they  form  with  the 
latter  one  connected  frame-work.  It  is  the  axis  of  their  princi- 
pal motions,  the  common  fulcrum  round  which  they  all  revolve. 
It  has  an  intimate  mechanical  relation  wdth  all  the  parts  of  the 
body.  It  affords  attachment  to  the  great  muscles  which  move 
the  trunk  and  the  principal  joints  of  the  extremities.  It  contains 
and  gives  protection  to  that  important  organ,  the  spinal  cord, 
from  which,  as  we  have  seen,  almost  all  the  nerves  of  the  body 
take  their  origin,  and  which  is  unquestionably,  next  to  the  brain, 
the  most  essential  organ  in  the  economy.  Whilst  the  spinal 
column  performs  these  offices,  it  is  at  the  same  time  capable  of 
considerable  flexion,  both  laterally  and  longitudinally;  and  admits 
also  of  some  degree  of  twisting  motion,  in  a  plane  perpendicular 
to  its  axis. 

237.  No  where  has  art  been  more  conspicuously  displayed 
than  in  the  construction  of  an  apparatus  adapted  to  fulfil  such 
opposite  and  apparently  incompatible  functions.  To  secure  the 
firmness  and  strength  which  are  required  in  the  basis  of  support 
to  the  whole  body,  in  the  key-stone,  as  it  were,  of  its  various 


120  MECHANICAL    FUNCTIONS. 

arches,  whilst  it  is  at  the  same  time  rendered  capable  of  so  great 
a  variety  of  motions,  objects  "which  seem  utterly  at  variance  with 
its  also  affording  protection  to  a  tender  and  delicate  organ,  in 
which  the  least  pressure  would  be  attended  with  fatal  conse- 
quences, must  be  allowed  to  be  a  most  difficult  problem  of 
mechanism.  And  yet  these  various,  complicated,  and  apparently 
inconsistent  ofhces,  we  find  executed  by  one  and  the  same  instru- 
ment. Flexibility  is  obtained  by  subdividing  it  into  a  great  num- 
ber of  small  portions,  each  of  which  is  separately  allowed  but  a 
small  degree  of  bending  upon  the  next;  and  thus  a  considerable 
motion  is  obtained  in  the  whole  column,  with  but  a  very  incon- 
siderable one  at  each  joint.  Each  bone,  as  was  described  in  the 
account  of  its  anatomy,  is  connected  with  its  neighbour  by  a 
broad  basis  of  attachment;  and  the  slight  relative  motions  of 
which  they  are  susceptible  are  chiefly  entrusted  to  the  lateral 
articulations.  Whilst  these  broad  bones  give  the  whole  chain 
its  requisite  firmness  and  stability,  they  are  so  constructed  as  to 
afford  a  passage,  without  any  diminution  of  their  strength,  to  the 
substance  of  the  spinal  marrow.  For  this  purpose  each  of  the 
bodies  is  hollowed  out  so  as  to  form  a  continued  groove  all  down 
the  back;  and  over  this  groove  a  broad  arch  is  thrown  from 
each  side,  converting  it  into  a  complete  canal.  In  order  to  pre- 
serve the  continuity  of  this  canal,  and  prevent  the  vertebrae  from 
shifting  upon  one  another  so  as  to  spread  upon  the  spinal  cord 
within,  during  the  various  movements  of  the  body,  further  securi- 
ties are  provided.  They  are  severally  connected  together  by 
their  projecting  processes,  which  lock  into  one  another,  and  are 
still  more  firmly  secured  by  the  ligaments  that  bind  them  down 
on  every  side.  Thus,  the  bodies  of  the  vertebrae  are  guarded 
against  the  danger  of  accidental  slipping,  but  they  are  defended 
also  from  displacement  by  any  force  short  of  what  would  break 
the  bone. 

238.  But  besides  all  these  provisions  the  vertebral  column  is 
protected  from  injury  arising  from  violent  jolts  or  jars  by  having 
interposed  between  each  adjoining  vertebrae,  the  peculiar  springy 
substance  known  by  the  name  of  the  intervertebral  cartilage  or 
ligament ;  for  it  in  reality  partakes  of  the  nature  of  both  these 
textures.  It  is  a  substance  quite  peculiar  to  this  part  of  the  frame. 
Its  compressibility  and  the  elastic  force  with  which  it  recovers 
its  shape  when  relievedfrom  the  compressing  power,  must  greatly 
lessen  the  quantity  of  motion  required  of  each  bone  during  the 
flexion  of  the  column,  as  well  as  soften  all  the  concussions  inci- 
dent to  violent  motion.  No  chasm  is  left  by  their  separation 
when  the  spine  is  bent ;  and  the  unity  of  the  whole  column,  and 
of  the  channel  in  its  centre,  is  preserved  unbroken.  A  passage  is 
at  the  same  time  allowed  between  each  contiguous  vertebra  for 


FUNCTIONS    OP    THE    OSSEOUS    FABRIC.  121 

the  nerves  which  issue  in  pairs  from  the  spinal  cord,  to  distribute 
their  branches  and  filaments  to  every  part  of  the  body. 

239.  The  natural  curvatures  in  the  line  of  the  vertebral  column 
also  contribute  materially  to  the  elasticity  of  the  whole  frame- 
work. On  receiving  any  shock  in  the  direction  of  its  length,  the 
impulse,  instead  of  being  propagated  the  whole  length  of  its  line, 
is  diverted  from  its  course  and  taken  off  by  the  flexures  of  the 
column;  and  the  maintenance  of  its  natural  position  is  effected 
more  by  the  power  of  the  muscles  attached  to  the  spine,  than  by 
its  inherent  elasticity. 

'  5.   The  Pelvis. 

240.  The  broad  expansion  of  bone  which  extends  on  each  side 
of  the  pelvis,  and  the  extremities  of  which  form  the  hips,  are 
evidently  designed  as  a  basis  of  support  for  the  viscera  of  the 
abdomen.  The  lower  portion  of  the  bones  of  the  pelvis  is  at  the 
same  time  rendered  light  by  being  formed  into  several  arches  ; 
strengthened  at  the  points  where  it  is  exposed  to  the  greatest  pres- 
sure, and  at  the  same  time  affording  room  for  the  articulations  of 
the  thigh  bones. 

8.   The  Limbs  in  General. 

241.  The  third  office  of  the  skeleton  is  to  furnish  levers  for 
accomplishing  the  progression  and  other  movements  of  the  body, 
which  require  great  force,  great  extent,  and  great  precision  of 
motion.  These  objects  are  attained  by  the  limbs,  which,  as  is 
well, known,  are  divided  into  separate  portions,  obviously  for  the 
purpose  of  increasing  the  facility  of  adaptation  to  a  great  variety 
of  movements  and  of  actions  which  the  individual  may  be  called 
upon  to  perform. 

242.  The  principal  bones  of  the  extremities  have  the  shape  of 
lengthened  cylinders,  and  compose  a  system  of  levers  adapted  to 
the  regular  and  accurate  appUcation  of  the  moving  force,  and  for 
the  execution  of  rapid,  extensive,  and  powerful  movements.  The 
circumstance  of  their  hollow  and  cancellated  structure  is  a  pal- 
pable instance  of  provident  adaptation  to  the  office  for  which 
they  are  framed.  It  may  be  mathematically  demonstrated,  that 
if  the  quantity  of  materials  assigned  for  the  construction  of  the 
bone  be  given,  there  is  no  mode  in  which  those  materials  could 
have  been  more  advantageously  disposed  for  resisting  a  trans- 
verse force  ;  that  is,  a  force  tending  to  break  it  across,  than  the 
form  of  a  tube,  or  hollow  cylinder,  which  is  that  actually  given 
to  them  by  nature.  If,  for  instance,  the  same  quantity  of  matter 
had  been  collected  into  a  solid  cylinder  of  the  same  length,  it 
would  have  been  subject  to  fracture  by  a  much  smaller  force  than 

11 


122  kECHANICAL    FUNCTIONS. 

that  which  it  bears  without  injury  in  its  actual  tubular  form. 
This  remark  was  long  ago  made  by  the  elder  Dr.  Monro,*  who 
observes  that  the  resistance  opposed  by  a  body  of  cylindrical 
shape  to  a  force  applied  transversely  is  in  the  direct  ratio  of  its 
diameter ;  hence  the  same  number  of  fibres  disposed  round  the 
circumference  of  a  circle  in  such  a  way  as  that  their  sections 
would  present  the  appearance  of  a  ring,  will  resist  with  greater 
force  than  if  they  had  been  united  at  the  centre,  so  that  their  section 
would  present  a  circle  of  much  smaller  diameter  than  the  ring. 
The  hollow  cylindrical  bones  are  accordingly  found  in  those 
situations  where  the  power  of  resisting  external  force  is  princi- 
pally wanted,  while  it  is  at  the  same  time  an  object  of  importance 
not  to  add  unnecessarily  to  the  weight.  A  simple  experiment 
will  illustrate  in  a  very  striking  manner  this  proposition.  Let  a 
cylindrical  glass  rod  and  a  glass  tube  be  taken  of  the  same  length 
and  also  of  the  same  weight,  so  that  they  may  both  contain  the 
same  quantity  of  materials.  If  each  be  then  supported  at  their 
two  ends,  on  a  frame  adapted  to  the  purpose,  it  will  be  found  that 
the  same  weight  which,  when  hung  from  the  rod,  will  break  it 
asunder,  will,  when  transferred  to  the  tube,  be  sustained  without 
even  bending  it  in  any  sensible  degree.  Dr.  Porterfield  has  given 
an  elaborate  mathematical  demonstration  of  the  general  proposi- 
tion.! 

243.  There  are  few  subjects'  in  physiology  v^'hich  present  so 
many  interestirrg  points  of  inquiry,  or  afford  more  abundant  proofs 
of  intelligence  and  design  than  the  mechanical  properties  of  the 
osseous  fabric.  From  the  account  we  formerly  gave  of  the 
composition  of  bone,  it  appears  that  it  is  constructed  of  two 
principal  materials,  an  earthy  basis,  which  is  the  phosphate  of 
lime,  and  an  animal  or  membranous  substance,  which  possesses 
considerable  tenacity.  To  the  first  of  these  ingredients  the  bones 
owe  their  solidity  and  hardness.  No  inorganic  matter,  not  even 
the  metals,  has  so  great  a  cohesive  power,  with  a  given  weight 
of  materials,  as  the  earthy  bodies ;  and  this  is  probably  the  reason 
why  the  phosphate  of  lime  has  been  selected  as  the  substance 
employed  to  give  the  necessary  solidity  and  hardness  to  bones. 
But  these  qualities,  if  carried  to  excess,  would  be  accompanied 
with  brittleness.  To  guard  against  this  evil,  the  cohesion  of  the 
inorganic  earth  is  tempered  by  the  interposition  of  an  elastic 
organic  material ;  this  is  the  cellular  tissue,  within  the  cells  of 
which  the  bony  matter  is  deposited,  and  which  acts  the  part  of 
a  cement,  binding  them  more  strongly  together,  and  at  the  same 
time  obviating  the  excessive  brittleness  which  a  substance  of  more 
uniform  hardness  would  have  possessed.     Thus,  by  the  admirable 

*  Anatomy  of  the  Bones  and  Muscles,  p.  21. 
f  Edinburgh  Medical  Essays,  vol.  i.  p.  95. 


FUNCTIONS    OF    THE    OSSEOUS    FABRIC.  123 

blending  of  these  two  elements,  two  qualities— which,  in  masses 
of  homogenous  and  unorganized  matter  are  scarcely  compatible 
with  one  another — are  happily  united. 

244.  The  manner  in'  which'the  cylindrical  bones  are  connected 
together  is  also  highly  deserving  of  attention.  There  are,  indeed, 
few  parts  of  the  mechanism  of  ajiimals  more  peculiarly  fitted  to 
excite  our  admiration  than  the  structure  of  the  joints.  Every 
provision  seems  to  have  been  made  for  facilitating  their  motion, 
and  every  precaution  taken  to  enable  them  to  act  with  safety. 
Their  ends  are  enlarged  for  the  purpose  of  affording  a  broader 
surface  of  junction,  and  for  procuring  greater  firmness  and 
security  of  connexion.  The  rough  and  hard  substance  of  bones 
would  have  been  particularly  exposed  to  injury  if  they  had  been 
allowed  to  grate  upon  one  another  without  some  intervening 
smooth  surface.  In  all  the  joints,  at  the  places  where  the  ends 
of  the  bone  would  have  suffered  from  this  cause,  we  find  them 
tipped  with  a  white,  smooth,  and  elastic  cartilage.  Dr.  Paley* 
has  very  aptly  compared  this  expedient  to  the  plating  of  a  naetal- 
lic  instrument  with  a  different  metal.  Detached  portions  of  car- 
tilage, are,  as  we  have  seen,  frequently  placed  between  the  bones, 
which  thus,  instead  of  working  upon  each  other,  work  upon  the 
intermediate  cartilages.  This  is  analogous  to  the  contrivance 
practised  by  mechanics,  who  interpose  a  loose  ring  where  the 
friction  of  the  joints  of  any  of  their  machines  is  great,  and  who 
particularly  resort  to  it  where  some  strong  and  heavy  work  is  to 
be  done.  It  is  precisely  under  similar  circumstances  that  the 
same  contrivance  is  employed  in  the  human  body;  and  the  ana- 
logy is  a  striking  evidence  of  that  art  and  foresight  which  are 
manifested  in  the  plan  of  its  conformation.  The  lubricating 
quality  of  the  synovia  is  also  an /exquisite  provision  designed  to 
diminish  friction.  i 

245.  The  ligaments  which  bind  the  ends  of  the  bones  together, 
and  restrain  the  direction  of  their  motions,  are  admirably  cal- 
culated to  perform  the  offices  assigned  to  them.  Like  the  bones, 
they  unite  qualities  which  are  rarely  met  with  in  conjunction. 
They  have  all  the  properties  we  can  desire  in  a  rope ;  namely, 
perfect  flexibihty,  with  great  power  of  resisting  extension.  It  is 
hardly  imaginable  how  great  a  force  is  required  to  stretch,  or 
rather  to  break  asunder  a  ligament,  for  it  will  not  yield  in  any 
sensible  degree  until  the  force  is  increased  so  as  at  on,ce  to  tear 
it  to  pieces.  Yet  with  all  this  toughness,  it  is  so  flexible  as  to 
oppose  no  impediment  to  the  suppleness  of  the  joint.  "  Every 
joint,"  says  Dr.  Paley,  "  is  strictly  a  mechanical  instrument,  and 
as  manifestly  contrived,  and  as  accurately  defined  as  any  that 
can  be  produced  out  of  a  cabinet  maker's  shop.    Their  durability 

*  Natural  Theology. 


124  MECHANICAL    FUNCTIONS. 

is  no  less  astonishing.  A  limb  shall  swing  upon  its  hinge,  or  play 
in  its  socket,  many  hundred  times  in  an  hour,  for  sixty  years  to- 
gether, without  diminution  of  its  agility."* 

7.   The  Lower  Extremities. 

246.  The  three  portions  into  which  the  lower  extremities  are 
divided,  namely  the  thigh,  leg,  and  foot,  being  united  by  joints, 
and  moveable  upon  one  another,  are  calculated  to  serve  the  double 
purpose  of  firm  columns  of  support  to  the  body  while  standing, 
and  of  facilitating  and  regulating  its  movements  while  advancing. 
It  might,  on  a  superficial  view  of  the  subject,  be  supposed  that, 
in  standing  in  the  erect  posture,  the  weight  of  the  body  would 
be  more  firmly  and  effectually  supported  had  the  whole  Jimb 
consisted  of  a  single  straight  column.  But,  independently  of  the 
greater  strain  to  which  such  a  structure  would  be  exposed,  in 
consequence  of  the  great  length  of  bone  required,  it  would,  in 
fact,  have  had  less  stabiHty  than  it  now  possesses.  A  marble 
statue  of  a  man  resting  merely  on  the  feet  in  a  natural  attitude, 
would  be  overthrown  by  a  small  impulse;  and  even  in  the  living 
body,  it  is  an  infalHble  consequence  of  the  laws  of  mechanics,  that 
if  ever  the  perpendicular  line  drawn  from  the  centre  of  gravity 
happen  to  pass  beyond  the  base  of  support,  the  body  must  in- 
evitably fall  in  spite  of  every  muscular  exertion  that  can  be  made. 
The  only  way  to  prevent  such  an  accident  is  to  bring  back  the 
centre  of  gravity  nearer  to  a  point  above  the  centre  of  the  base 
before  it  has  actually  passed  it ;  and  this  we  instinctively  do  when 
we  feel  ourselves  in  danger  of  falling  to  one  side,  by  extending 
the  arm  horizontally  on  the  opposite  side. 

247.  But  the  limb  being  divided  into  joints,  these  joints  would 
give  way  under  the  weight  of  the  body,  were  they  not  prevented 
from  bending  by  the  constant  action  of  the ,  muscles.  Th6  con-/ 
tinual  muscular  effort  required  in  standing  is  nearly  as  great  an 
expenditure  of  muscular  power  as  the  act  of  walking.  Soldiers 
on  parade,  remaining  in  the  same  attitude,  experience  even  more 
fatigue  than  they  would  suffer  by  a  march  during  an  equal  time, 
because  the  same  muscles  are  constantly  in  action.  The  posture 
of  a  soldier  under  arms,  with  his  thighs  and  legs  in  the  same 
straight  line,  is  one  which  requires  a  painful  effort  to  preserve. 
The  moment  the  word  of  command  is  given  him  to  "  stand  at 
ease,"  the  muscles  on  one  side  immediately  relax,  the  right  knee 
is  slightly  bent,  the  tension  of  the  ankle-joint  is  relieved,  and  the 
body,  sinking  upon  the  left  hip,  has  its  height  diminished  by  above 
an  inch  and  a-half.  The  weight  of  the  trunk  is  sustained  more 
directly  by  the  column  of  bones  of  the  left  limb,  which  support 

f  Natural  Theology. 


FUNCTIONS    OP    THE    OSSEOUS    FABRIC.  125 

that  weight  at  a  greater  mechanical  advantage  than  before  ;  for 
the  oblique  direction  of  the  neck  of  the  thigh  bone,  with  regard 
to  the  bones  of  the  pelvis,  which  is  very  great  in  the  perfectly 
erect  position,  is  now  diminished.  Bui  the  great  source  of  relief 
is  that  a  diflerent  set  of  muscles  is  called  into  play  on  every 
change  of  posture ;  those  which  were  before  fatigued  have  time 
to  recruit  their  energies,  and  become  prepared  afterwards  to 
afford  in  their  turn  the  same  relief  to  others  by  resuming  their 
exertions. 

248.  Strictly  speaking,  it  is  quite  impossible  for  even  the 
strongest  man^  remain  for  even  a  very  short  interval  of  time 
in  precisely  the  same  position.  The  fatigue  of  the  muscles  which 
are  in  action  soon  become  sensible,  and  relief  is  instantly  given 
to  them  by  varying  the  points  of  support.  Thus  we  may  observe, 
that  in  standing,  the  weight  of  the  body  is  naturally  thrown  al- 
ternately from  one  foot  to  the  other.  The  action  of  standing  must 
be  considered  as  a  series  of  perpetual,  but  obscure  movements, 
by  which  the  centre  of  gravity  is  continually  shifted  from  one 
part  of  the  base  to  the  other  ;  the  tendency  to  fall  in  any  one  , 
direction  being  perpetually  counteracted  by  small  and  insensible 
movements  in  the  contrary  direction.  Long  habit  has  rendered 
us  unconscious  of  these  exertions,  and  inattentive  to  the  sensations 
which  prompt  them.  But  a  child,  when  acquiring  the  art  of 
walking,  is  sensible  of  all  these  difficulties,  and  does  not  learn  to 
walk  but  by  reiterated  lessons,  and  by  the  experience  of  many 
falls.  It  is  by  a  practice  of  the  same  kind,  and  continued  during 
a  longer  period,  that  the  rope-dancer  learns  to  support  himself 
on  a  narrower  or  more  unstable  base  than  that  which  nature  has 
provided.  This  he  effects,  not  by  keeping  his  centre  of  gravity 
precisely  in  the  mathematical  perpendicular  to  the  rope,  but  by 
continually  shifting  it  from  side  to  side  ;  never  allowing  it  to  fall 
above  a  certain  very  minute  distance,  and  immediately  correcting 
the  vacillation  by  a  movement,  which  gives  it  an  impulse  in  the 
contrary  direction. 

249.  The  flexures  of  the  joints  of  the  lower  extremities,  it  may 
be  observed,  take  place  alternately  in  opposite  directions.  Thus 
the  thigh  is  bent  forwards  upon  the  pelvis;  the  leg  is  bent  back- 
wards upon  the  thigh;  and  the  foot,  again,  is  bent  forwards  upon 
the  leg.  This  arrangement  is  obviously  the  one  best  adapted  to 
convenience,  both  as  regards  the  folding  of  the  parts  when  bent, 
and  the  commodious  disposition  of  the  muscles,  which  perform 
the  opposite  motions  of  flexion  and  extension.  As  the  weight 
of  the  body  occasions  the  flexion  of  the  joints,  so  it  is  that  flexion, 
which  the  muscles  are  chiefly  required  to  counteract;  and  this  is 
the  duty  of  the  extensor  muscles.  We  accordingly  find,  that 
in  each  joint  the  latter  are  much  larger,  and  more  powerful  than 
the  flexors.     They  are  enabled  also  to  act  with  greater  mechan- 


126  MECHANICAL    FUNCTIONS. 

ical  advantage,  in  consequence  of  their  being  inserted  into  pro- 
jecting processes  of  the  bones,  evidently  provided  with  this  express 
intention.  This  is  the  purpose  of  the  trochanter  of  the  thigh 
bone,  and  the  projecting  bone  of  the  heel.  The  same  object  is 
accomplished,  in  a  still  more  artificial  manner,  in  the  knee-joint, 
by  an  additional  bone,  the  jpatella,  or  knee-pan,  into  which  the 
great  extensor  muscles  situate  in  the  fore  part  of  the  thigh  are 
inserted,  and  which  renders  their  action  much  more  efficient,  both 
by  diminishing  its  obliquity,  and  by  removing  it  farther  from  the 
centre  of  rotation.  It  acts,  therefore,  as  a  pulley,  which  is  a 
species  of  lever;  and  it  is  so  contrived,  that  while  the  knee  is 
bent,  and  the  muscles  at  rest,  as  when  we  are  sitting,  this  bone 
sinks  down,  concealed  in  a  hollow  of  the  knee.  When  the 
extensor  muscles  begin  to  act,  they  draw  out  the  patella  from  this 
hollow;  and  in  proportion  as  they  contract,  and  their  strength 
diminishes,  the  patella  gradually  rising,  gives  greater  mechanical 
advantage  to  their  action,  which  is  greatest  of  all  when,  by  their 
complete  contraction,  their  power  is  most  expended. 

250.  The  structure  of  the  feet  is  also  admirably  contrived,  as 
a  secure  basis  for  their  support  of  the  whole  superincumbent 
weight  of  the  body,  and  of  all  the  additional  burdens  which  the 
body  may  be  made  to  sustain.  The  arrangement  of  the  bones  is 
in  as  strict  conformity  to  the  principles  of  the  arch  as  those  of  the 
skull.  The  bones  of  the  tarsus  constitute  what  may  be  called  a 
double  arch ;  that  is,  an  arch  in  two  different  places  at  right 
angles  to  one  another.  There  is,  in  the  first  place,  one  great 
longitudinal  arch,  springing  from  the  point  of  the  heel  to  the  ball 
of  the  great  toe ;  and  there  is,  in  the  second  place,  a  transverse 
arch  formed  among  the  tarsal  bones  themselves,  one  within 
another.  Near  the  heel  this  arch  is  composed  of  the  astragalus, 
OS  calcis,  and  naviculare;  and  farther  on,  by  the  cuneiform  or 
wedge-like  bones,  the  name  of  which  expresses  their  office,'  ana- 
logous to  that  of  the  stones  at  the  crown  of  an  arch  of  masonry. 
The  elasticity,  as  well  as  security,  resulting  from  all  these  arches, 
imparts  that  ease  and  spring  so  remarkable  in  the  step,  and 
obviates  the  injurious  jar  that  would  be  otherwise  inevitably  com- 
municated to  the  body  by  leaps,  by  falls,  or  other  accidents. 

251.  In  walking,  the  first  action  consists  in  fixing  one  foot 
firmly  on  the  ground,  by  transferring  to  it  the  whole  weight  of 
the  body  ;  the  other  foot  being  then  at  liberty  to  move,  is  with 
t^e  leg  carried  forwards.  This  projection  of  the  limb  is  neces- 
sarily attended  with  a  corresponding  advance  of  the  centre  of 
gravity,  which  proceeds  to  move  forwards  till  it  arrives  beyond 
the  basis  of  the  foot  on  which  the  body  is  resting.  Whenever 
this  happens,  the  body,  being  unsupported,  begins  to  fall,  and 
would  continue  to  fall,  wei'e  not  the  other  foot  in  advance,  and 
ready  to  receive  it,  and  stop  its  further  descent.     This  is  the 


FUNCTIONS    OF   THE    OSSEOUS    FABRIC.  127 

reason  why  we  experience  so  disagreeable  a  jar,  if  in  walking 
inattentively,  the  foot  we  had  advanced  Ijappens  to  arrive  at  a 
lower  level  on  the  ground  than  had  been  expected ;  as  when,  for 
instance,  we  meet  with  a  descending  step  for  which  we  were 
not  prepared.  The  body  on  these  occasions,  falHng  through 
greater  space  than  usual,  acquires  a  certain  velocity  of  descent, 
and  this  unusual  velocity  being  suddenly  checked,  communicates 
a  shock  to  the  whole  system. 

252.  While  the  weight  of  the  body  is  thus  transferred  alter- 
nately from  one  foot  to  the  other,  the  centre  of  gravity  of  the 
body,  while  it  is  continually  carried  forwards,  is  at  the  same  time 
alternately  raised  and  lowered,  so  as  to  describe  at  each  step  a 
small  arch;  and  its  whole  motion  may  be  represented  by  a 
waving  line,  having  lateral  as  well  as  longitudinal  inflexions,  and 
composed  of  a  succession  of  short  curves.  In  taking  long  steps, 
we  are  obliged  to  raise  the  centre  of  gravity  through  a  longer 
arch,  and  therefore  to  a  greater  height.  This  is  consequently 
more  fatiguing  than  a  shorter  step.  If,  however,  we  go  into  the 
contrary  extreme,  and  take  too  short  steps,  the  advantage  ob- 
tained in  lessoning  the  height  of  the  arches  described  by  the 
centre  of  gravity,  is  more  than  compensated  by  the  greater 
quickness  required  in  the  motions  necessary  for  keeping  up  the 
same  rate  of  walking. 

253.  The  lateral  undulation  of  the  body  during  walking  is 
iiever  performed  with  precise  equality  on  both  sides ;  and  the 
amount  of  the  accumulated  deviations  would  be  considerable, 
did  we  not  avail  ourselves  of  the  assistance  of  the  sense  of  sight 
in  counteracting  it.  This  will  appear  from  the  well-known  fact, 
that  it  is  impossible  for  a  person  who  is  blindfolded  to  continue 
to  walk  in  a  straight  line  for  any  considerable  distance.  Even 
on  a  perfectly  level  plain,  we  unavoidably  inchne  to  the  right  or 
to  the  left ;  and  the  want  of  consciousness  that  we  are  doing  so, 
prevents  us  from  rectifying  the  error;  so  that  while  we  imagine 
we  have  undeviatingly  pursued  a  straight  course,  we  may  per- 
haps, when  the  bandage  is  removed  from  our  eyes,  find  ourselves 
near  the  very  spot  from  whence  we  had  commenced  our  circum- 
ambulatory  excursion. 

8.   The  Upper  Extremities. 

254.  The  upper  extremity,  though  exempt  from  the  ofiice  of 
supporting  any  part  of  the  weight  of  the  trunk,  and  intended  for 
a  variety  of  very  different  uses,  presents  us  with  exactly  the  same 
number  of  divisions  as  the  lower  extremities ;  excepting  that  in 
the  skeleton,  if  we  compare  the  scapula  to  the  bones  of  the  pelvis, 
there  is  an  additional  bone  provided  in  the  clavicle,  or  collar 
bone,  by  means  of  which  the  bones  of  the  arm  are  articulated 


128  MECHANICAL    FUNCTIONS. 

with  those  of  the  trunk.  The  extremity  of  the  clavicle,  indeed, 
by  which  it  joins  the  sternum,  is  the  pivot  on  which  all  the  great 
motions  of  the  arm  are  performed.  The  interposition  of  the 
scapula  is  evidently  for  the  purpose  of  giving  a  more  extended 
surface  for  the  attachment  of  the  strong  muscles  destined  to  act 
upon  the  arm  and  upper  part  of  the  trunk,  and  which  also  lend 
their  aid  in  performing  the  movements  necessary  for  respiration. 
It  also  contributes  its  share  in  the  defence  of  the  back  part  of  the 
chest. 

255.  The  joint  of  the  shoulder  is  of  the  ball  and  socket  kind, 
and  admits,  therefore,  of  the  greatest  latitude  of  motion.  That 
of  the  elbow  is  a  simple  hinge-joint,  and  restricted  consequently 
to  mere  flexion  and  extension.  A  rotatory  motion  was  here  unne- 
cessary ;  for  the  free  rolling  of  the  arm  at  the  shoulder  answ^ers 
every  purpose  that  can  be  desired,  and  the  elbow -joint  is  rendered 
more  secure  by  this  limitation  of  its  motion ;  for  it  will  always 
be  'found,  that  whenever  a  hinge-joint  is  sufficient  for  the  pur- 
poses required,  it  is  employed  in  prefei^ence  to  that  of  the  ball  and 
socket,  which,  from  its  very  extensive  range  of  motion,  must 
necessarily  be  looser  in  its  structure,  and  more  liable  to  disloca- 
tion. 

256.  In  the  wrist,  which  is  the  great  centre  of  all  the  motions 
of  the  hand,  a  construction  was  called  for  which  might  allow  of 
the  utmost  latitude  of  motion.  The  following  were  the  three 
kinds  of  movement  required  ;  first,  simple  flexion  and  extension; 
secondly,  lateral  flexions ;  and,  thirdly,  twisting,  or  rotation  of 
the  hand,  as  when  it  is  employed  in  turning  a  screw.  If  all 
these  different  motions  had  been  entrusted  to  a  simple  ball  and 
socket  joint,  they  could  not  have  been  well  performed  without 
great  strains  and  hazard  of  dislocation.  This  danger  is  admira- 
bly obviated  by  distributing  the  motions  among  several  articula- 
tions. No  part  of  the  bony  system  is  more  complex  than  the 
wrist,  which  consists  of  eight  small  bones  crowded  into  a  very 
narrow  space,  and  lashed  together  by  many  strong  ligaments, 
that  form  bands  crossing  one  another  in  every  possible  direction. 
While  they  are  together  fitted  to  the  bones  of  the  fore-arm  in  the 
manner  of  a  hinge-joint,  their  mutual  connexions  allow  at  the 
same  time  of  considerable  lateral  flexion. 

257.  But  still  the  rotatory  or  twisting  motion  of  the  hand, 
which  is  perhaps  the  most  useful  of  all,  is  not  provided  for  by  this 
mechanism.  For  the  accomplishment  of  this  object  there  is 
employed  a  contrivance  to  -v^hich  the  rest  of  the  system  presents 
nothing  similar.  The  wrist  is  connected  not  so  much  with  the 
principal  bone  of  the  fore-arm,  as  with  a  subsidiary  bone  of  equal 
length  with  it,  and  placed  in  a  parallel  position,  termed  the  i^adius ; 
and  its  peculiar  mode  of  junction  is  such  as  to  enable  it  to 
describe  round  the  former  a    complete  semicircle.      In  these 


FUNCTIONS    OP    THE    OSSEOUS    FABRIC.  129 

rolling  motions  the  radius  carries  along  with  it  the  hand,  which 
thus  turns  in  perlect  security;  for  it  is  difficult  to  conceive  how 
a  force  could  well  be  applied,  so  as  to  separate  bones  having  so 
long  a  lever  of  resistance.  Thus,  while  the  wrist  is  exempt  from 
the  weakness  incident  to  circular  joints,  it  possesses  all  the  pro- 
perties which  we  find  in  the  most  moveable. 

258.  The  manner  in  which  the  fingers  are  disposed  in  the 
hand,  like  radii  from  a  common  centre,  is  such  as  to  allow  them 
very  free  play,  and  to  extend  their  sphere  of  action.  But  the 
chief  perfection  of  the  hand,  as  a  mechanical  instrument  of 
prehension,  consists  in  the  structure  of  the  thumb,  which  is  fur- 
nished with  muscles  of  so  great  a  strength,  compared  with  those 
of  the  fingers,  as  to  enable  it  to  oppose  and  balance  their  united 
power.  Hence  the  hand  is  capable  of  grasping  a  spherical  body, 
and  of  keeping  firm  hold  of  a  variety  of  objects,  which  it  would 
otherwise  have  required  the  concurrence  of  both  hands  to  retain. 

259.  The  passage  of  the  tendons,  by  which  the  fingers  are 
bent,  is  particularly  deserving  of  notice,  and  has  often  been 
appealed  to  as  a  signal  instance  of  express  contrivance.  As  the 
uses  of  the  hand  require  the  beading  of  each  joint  of  the  fingers 
independently  of  the  others,  it  was  necessary  that  separate  muscles 
and  separate  tendons  should  be  provided  for  each.  The  muscles 
are  most  advantageously  placed  high  up  in  the  arm,  and 
convenience  requires  that  those  muscles  which  bend  the  last 
joints  should  He  beneath  those  that  bend  the  middle  joints. 
Had  the  tendons  proceeding  from  the  latter  been  directly  inserted 
into  the  middle  of  the  second  bone  of  the  finger,  they  would  have 
been  exactly  in  the  way  of  the  tendons  which  are  underneath, 
and  which  are  proceeding  to  a  more  distant  insertion.  They 
are  therefore  split  into  two  branches,  each  being  inserted  into  the 
side,of  the  bone;  and  the  lower  tendon  is  thus  allowed  to  pass  on 
securely  between  them.  This  structure  has  also  this  further  advan- 
tage, that  it  procures  a  morereadyflexionof  the  last  joint  than  of  the 
other  joints  ;  a  provision,  the  pui'pose  of  which  is  manifest,  since 
it  tends  effectually  to  prevent  the  escape  of  the  object  we  wish 
to  lay  hold  of  "  There  is  nothing,"  says  Dr.  Paley,  "  in  a  silk 
or  cotton  mill,  in  the  belts,  straps,  or  ropes,  by  which  motion  is  com- 
municated from  one  part  of  the  machine  to  the  other,  that  is  more 
artificial,  or  more  evidently  so  than  this  perforation."  "  Let  a 
person  observe  his  own  hand  while  he  is  writing,  the  number  of 
muscles  that  are  brought  to  bear  upon  the  pen,  how  the  joint  and 
adjusted  operation  of  several  tendons  is  concerned  in  every  stroke, 
yet  that  five  hundred  such  strokes  are  drawn  in  a  minute.  Not 
a  letter  can  be  turned  without  two  or  three  tendinous  contractions, 
definite  both  as  to  the  choice  of  the  tendon,  and  as  to  the  space 
through  which  it  moves.  Yet  how  correctly  does  the  work  pro- 
ceed ;  how  faithful  have  the  muscles  been  to  their  duty;  how 
true  to  the  order  which  endeavour  or  habit  has  inculcated.     Let 


130  NUTRITIVE    FUNCTIONS. 

US  watch  the  hand  while  playing  upon  a  musical  instrument. 
All  the  changes  produced,  though  extremely  rapid,  are  exactly 
measured,  even  when  most  minute  ;  and  display  on  the  part  of 
the  muscles  an  obedience  of  action  alike  wonderful  for  its  quick- 
ness and  its  correctness." 

260.  To  specify  all  the  instances  of  express  contrivance  in  the 
mechanical  conformation  of  the  hand  would  fill  a  volume.  As 
an  organ  of  touch  it  is  admirably  formed.  No  instrument  is  bet- 
ter adapted  to  the  practice  of  the  mechanical  arts ;  none  could  be 
better  fitted  for  examining  the  properties  of  bodies,  and  the  laws 
of  the  material  world,  of  which  none  of  the  other  senses,  unassisted 
by  that  of  touch,  could  impart  to  us  any  accurate  knowledge. 
So  great  are  the  advantages  which  the  possession  of  this  organ 
has  conferred  upon  the  human  race,  that  many  philosophers,  prone 
to  paradox,  have  ascribed  to  this  circumstance  alone  the  whole 
of  the  intellectual  superiority  which  he  enjoys  over  the  brute 
creation. 


CHAPJ^ER  VI. 

ASSIMILATION. 

Sect.  I. — Chemical  Constitution  of  Organized  Matter. 

1.  JVecessity  of  Aliment. 

261.  A  coivsTANT  supply  of  nutritive  matter  is  necessary  for  the 
continuance  of  life,  a  necessity  arising  from  a  variety  of  causes. 
In  the  first  place,  the  substance  of  which  the  body  is  formed  is 
exposed  to  various  sources  of  waste  and  dissipation,  and  is  con- 
tinually verging  to  a  state  in  which  the  organs  become  unfit  for 
the  performance  of  their  functions.  The  chemical  affinities,  by 
which  the  elements  of  organized  substances  are  retained  in  that 
peculiar  mode  of  combination  which  constitutes  their  living  state, 
are,  as  we  shall  presently  see,  very  nicely  balanced,  and  would 
be  unable  to  preserve  them  in  that  condition  were  not  some 
means  provided  for  counteracting  their  natural  tendency  to 
decomposition.  By  the  active  exercise  of  their  respective  func- 
tions all  the  organs,  but  more  especially  the  muscular  and  nervous 
systems,  experience  a  deterioration  of  their  component  parts,  and 
suffer  decay  and  waste.  Fresh  materials  are  required  for  sup- 
plying this  continual  expenditure.  A  certain  degree  of  tempera- 
ture must  also  be  kept  up,  otherwise  the  muscles  would  lose  their 


CHEMICAL    CONDITIONS    OF    ORGANIZED    MATTER.  131 

faculty  of  contracting,  and  the  nerves  their  power  of  conveying 
impressions  to  and  from  the  sensorium.  Materials  are  therefore 
necessary  to  be  employed  as  fuel  for  keeping  up  the  vital  warmth. 
The  daily  consumption  of  combustible  materials,  apparently  used 
for  this  purpose  in  the  animal  economy,  is,  we  shall  afterwards 
find,  very  large,  and  forms  a  considerable  proportion  of  the  food 
received  into  the  body. 

262.  All  that  we  have  now  said  refers  to  the  body  in  its  adult 
or  mature  state,  when  it  has  attained  its  full  dimensions,  and  when 
all  that  is  required  is  its  preservation  in  that  state.  But  during 
all  that  period  of  life  when  the  body  is  increasing  in  its  size,  it  is 
evident  that  its  growth  can  only  take  place  in  consequence  of  the 
addition  of  new  particles  to  those  already  composing  the  sub- 
stance of  the  body ;  and  some  parts,  such  as  the  hair  and  nails, 
continue  to  grow  even  to  the  latest  period  of  life.  At  every  age 
some  part  is  liable  to  be  injured  or  destroyed,  and  a  provision  is 
in  most  cases  made  for  the  reparation  of  that  which  has  been 
injured,  or  even  for  the  replacement  of  that  which  has  been  de- 
stroyed. These  objects  can  be  effected  only  by  the  supply  of 
new  materials  derived  from  external  sources. 

The  changes  effected  by  the  long  series  of  assimilatory  pro- 
cesses being  essentially  chemical,  it  becomes  necessary  to  insti- 
tute a  particular  inquiry  into  the  chemical  constitution  of  organized 
substances  in  their  successive  stages  of  mutation,  from  the  most 
simple  to  the  more  complex  conditions  in  which  they  are  found 
to  exist  in  the  composition  of  an  animal  body. 

2.  Chemical  conditions  of  organized  matter. 

263.  The  parts,  which  by  their  assemblage  constitute  an 
organized  body,  when  compared  with  unorganized  matter,  ex- 
hibit in  ther  chemical,  as  well  as  in  their  mechanical  characters, 
the  most  well  marked  and  striking  contrast.  Complexity,  variety, 
and  difficulty  of  analysis,  are  the  leading  features  as  much  in  the 
former  as  in  the  latter  of  these  subjects  of  consideration.  Com- 
binations equally  artificial,  equally  the  result  of  design,  and  of 
refined  elaboration,  are  exhibited  both  in  the  mechanism  of  orga- 
nic structures,  and  also  in  the  chemical  constitution  of  organic 
substances.  Compared  with  the  latter,  all  the  bodies  which  are 
presented  to  us  in  the  mineral  kingdom,  are  extremely  simple ; 
and  their  study  presents  no  difficulties  of  an  insurmountable  na- 
ture. The  number  of  primary  or  elementary  substances,  or  of 
those  at  least  which  we  regard  as  simple,  is,  indeed,  greater  in 
the  mineral  kingdom,  than  that  of  those  which  enter  into  the 
composition  of  animal  or  vegetable  bodies ;  but  they  are  for  the 
most  part  found  united  in  binary  combinations,  or  arc,  at  least, 
easily  resolvable  into  a  small  number  of  such  binary  compounds. 


132  NUTRITIVE    FUNCTIONS. 

In  the  products  of  animal  or  vegetable  systems,  we  find  a  less 
variety  of  ultimate  principles  ;  but  this  is  more  than  compensated 
by  the  infinitely  greater  diversity  of  modes  in  which  they  are 
combined.  The  same  elements,  instead  of  forming  with  each 
other  mere  binary  combinations,  generally  exist  in  more  compli- 
cated states  of  union;  three,  four,  five,  or  even  a  greater  number 
of  constituent  substances,  having  their  affinities  nicely  balanced, 
and  harmonized  into  one  individual  combination. 

264.  From  this  diversity  in  the  mode  of  union,  there  arise 
remarkable  diflTerences  in  the  properties  of  different  organized 
products,  formed  from  the  same  ultimate  principles :  nor  can  we, 
as  in  bodies  belonging  to  the  mineral  kingdom,  with  an  exact 
knowledge  of  the  nature  and  proportions  of  the  component  sub- 
stances, proceed,  by  any  artificial  arrangement,  to  the  actual 
formation  of  the  compounds  themselves.  No  approach  has  yet 
been  made  by  human  ingenuity,  to  the  imitation  of  nature  in 
these  refined  operations  of  vitality. 

265.  Another  consequence  resulting  from  this  difference  in 
constitution  between  organized  products  and  the  inorganic  bodies 
of  the  mineral  kingdom,  is  that  the  affinities  by  which  the  ele- 
ments of  the  former  class  of  bodies  are  held  in  union,  being  nicely 
balanced,  are  more  subject  to  change.  The  equipoise  is  easily 
disturbed  and  subverted.  The  principles  have  a  constant  ten- 
dency to  react  on  each  other,  so  as  to  give  rise  to  a  new  order 
of  combinations;  which  readily  take  place  by  slight  alterations 
of  circumstances. 

266.  All  organic  products  are  susceptible  of  decomposition  by 
heat  alone ;  they  are  readily  acted  upon  by  various  agents,  as 
water  or  atmospheric  air ;  and  they  are  generally  liable  to  spon- 
taneous changes,  to  fermentation,  and  putrefaction. 

267.  Such,  then,  are  the  distinguishing  features  of  the  chemical 
properties  belonging  to  the  products  of  organization;  simplicity 
as  to  the  number  of  ultimate  elements  ;  complication  in  the  mode 
and  order  of  combination ;  unsteadiness  in  the  balance  of  affinities 
retaining  them  in  union,  and  consequent  proneness  to  decomposi- 
tion, and  impracticability  of  their  artificial  formation  by  a  reunion 
of  their  principles. 

268.  Whilst  the  products  of  the  animal  kingdom  participate 
with  vegetable  bodies  in  these  common  characters,  which  dis- 
tinguish them  from  inorganic  materials,  they  differ  from  the 
former  in  several  subordinate  circumstances  of  chemical  relation. 
The  constituent  principles  of  animal  substances  are  somewhat 
more  numerous,  and  their  affinities  more  nicely  adjusted,  and 
more  easily  disturbed.  Their  chemical  constitution  is  the  result 
of  still  more  delicate  processes,  and  of  a  more  elaborate  organi- 
zation. The  three  great  component  elements  of  all  vegetable 
bodies,  are  oxygen,  hydrogen,  and  carbon ;  but  animal  substances 


CHEMICAL    CONDITIONS    OF    ORGANIZED    MATTER.  133 

generally  contain,  besides  these,  a  considerable  proportion  of  a 
fourth  element,  namely  nitrogen,  the  presence  of  which  has  a 
considerable  influence  on  the  changes  they  undergo  when  sub- 
jected to  the  operation  of  foreign  agents,  or  left  to  the  spontaneous 
operation  of  internal  causes  of  decomposition.  P/iosphorus  and 
sulphur  must  also  be  enumerated  among  the  com,ponent  parts  of 
the  greater  number  of  animal  substances;  and  the  affinities  ex- 
erted by  these  elements  also  tend  to  modify  the  results  produced 
by  these  various  causes.  The  greater  the  number  of  elementary 
ingredients  present  in  any  assemblage,  the  greater  will  be  the 
tendency  to  form  binary  or  ternary  combinations  ;  and  the  more 
will  the  affinities  be  divided  between  difierent  elements,  and  pass 
easily  from  one  mode  of  arrangement  into  another.  Hence  the 
greater  susceptibility  to  decomposition  whichcharacterises  animal 
products  when  compared  with  vegetable. 

269.  In  addition  to  the  substances  already  mentioned,  we  must 
also  reckon  among  the  constituents  of  animal  substances, /m^, 
potash,  sdda,  and  iron  ;  but  these  exist  only  in  small  quantities. 

270.  Some  of  the  most  important  qualities  distinguishing  animal 
substances  are  owing,  in  particular,  to  the  predominance  of 
nitrogen  in  their  composition.  This  substance  is  disengaged  from 
them  in  large  quantities  by  the  action  of  the  nitric  acid.  This 
acid,  indeed,  itself  contains  nitrogen;  but  it  has  been  ascertained, 
that  in  producing  this  effect,  the  acid  does  not  undergo  any 
decomposition  ;  so  that  the  nitrogen  is  furnished  not  by  the  acid, 
but  entirely  by  the  substance  subjected  to  its  action.  Ammonia 
is  evolved  both  during  the  putrefaction  of  animal  substances,  and 
also  by  the  application  of  a  heat  sufficient  for  their  decomposi- 
tion ;  and  this  ammonia  results  from  the  combination  of  the  nitro- 
gen W'ith  hydrogen  during  these  processes.  Cyanogen,  or  prussic 
acid,  is  also  a  frequent  product  of  these  operations  ;  and  is  known 
to  consist  chiefly  of  nitrogen.  Under  these  circumstances,  also, 
the  phosphorus  enters  into  new  combinations,  particularly  with 
the  hydrogen  and  azote,  and  forms  compound  gases,  w^hich  are 
extricated  both  during  the  putrefaction  and  destructive  distillation 
of  animal  substances.  By  becoming  acidified  by  its  union  with 
oxygen,  it  enters  into  combination  with  earths,  alkalies,  and  oxide 
of  iron,  and  forms  a  variety  of  neutral  salts.  The  same  obser- 
vations also  apply  to  the  sulphur  which  is  found  in  certain  quan- 
tities in  several  animal  substances. 

271.  Another  general  difference  in  the  chemical  composition  of 
animal  and  of  vegetable  substances,  is  that  the  former  contain  a 
smaller  proportion  of  carbon,  and  a  greater  proportion  of  hydro- 
gen than  the  latter.  Carbon  may  be  regarded  as  the  base  of 
vegetable  matter,  to  which  oxygen  and  hydrogen  are  attached; 
while  hydrogen  appears  to  be  the  principal  component  part  of 
animal  matter,  and  is  there  combined  with  nitrogen,  oxygen, 

12 


134  KUTRITIVE    FUNCTIONS. 

carbon,  and  phosphorus.  Hence  during  the  decomposition  of 
animal  substances  by  heat,  the  chief  products  are  ammonia  and 
empyreumatic  oil,  in  both  of  which  hydrogen  is  a  principal  con- 
stituent. In  general  animal  matters  contain  less  oxygen  than 
vegetable,  and  hence  afford  less  acid  by  their  decomposition ; 
and  the  coal  which  remains  differs  from  vegetable  charcoal  in 
being  much  less  combustible. 


'& 


3.  Proximate  Animal  Principles. 

272.  In  the  numerous  and  diversified  products  of  the  animal 
kingdom,  we  may  trace  different  degrees  of  complication  in  the 
composition  of  their  elements.  Several  substances  present  the 
appearance  of  greater  simplicity,  and  appear  to  result  from  the 
more  direct  union  of  a  few  elements,  and  to  preserve  among 
various  shades  of  modification  the  same  general  properties,  and 
the  same  distinctive  characters.  The  more  compound  products 
often  admit  of  an  intermediate  analysis  into  these  comparatively 
simpler  constituents,  which  are  distinguishable  from  each  other 
by  a  certain  uniformity  of  character,  and  which  we  may  pre- 
sume are  obtained  in  the  same  state  as  that  in  which  they  existed 
in  the  compound  subjected  to  the  analysis.  These  form  what  are 
termed  the  intermediate  or  proximate  principles  of  animal  bodies, 
in  contradistinction  to  the  elementary  principles,  which  are  the 
result  of  the  ultimate  analysis  of  the  substance.  These  proximate 
principles  may  be  considered  as  forming  by  their  mixture,  or 
combination,  all  the  varieties  of  animal  matter;  and  they  are 
therefore  the  more  immediate  object  of  attention  to  the  chemist 
in  his  analysis  of  animal  substances. 

273.  The  only  method  resorted  to  by  the  earlier  chemists,  in 
the  infancy  of  science,  for  ascertaining  the  composition  of  ani- 
mal substances,  was  that  of  subjecting  them  to  the  process  of 
distillation  at  a  high  temperature,  by  which  their  proximate  prin- 
ciples were  entirely  destroyed,  and  either  converted  into  new 
compounds,  or  resolved  into  their  ultimate  elements.  Many  of 
these,  being  gaseous,  were  sufl^ered  to  escape,  and  were  totally 
disregarded.  Scarcely  any  light  could  be  thrown  upon  the  com- 
position of  animal  bodies  by  such  an  imperfect  mode  of  exami- 
nation. Successive  improvements  were  afterwards  introduced 
into  this  branch  of  chemical  research,  consisting  chiefly  in  the 
application  of  various  re-agents,  from  which  instructive  results 
were  derived. 

274.  The  modern  art  of  animal  analysis  may  be  considered 
as  comprising  three  different  kinds  of  operations,  which  however 
admit  of  being  variously  combined.  The  first  consists  in  observ- 
ing the  spontaneous  changes  resulting  from  various  natural 
circumstances  in  which  the  substances  may  be  placed  ;  the  second 


PROXIMATE    ANIiMAL    PRINCIPLES.  135 

depends  on  the  application  of  chemical  agents,  employed  either 
as  tests  to  indicate  the  existence  of  particular  elements  or  proxi- 
mate principles,  or  as  menstrua,  which  by  their  specific  affinities 
may  separate  the  elements  or  primary  compounds  from  each 
other ;  while  the  third  set  of  operations,  reverting  to  the  original 
plan  of  destructive  analysis,  effects  the  complete  decomposition 
of  the  substance,  but  carefully  collects  all  the  volatile  and  gaseous 
matter,  and  deduces  an  accurate  estimate  of  the  nature  and  pro- 
portions of  the  ultimate  elements.  We  obtain,  for  example,  a  cer-  " 
tain  quantity  of  water,  carbonic  acid,  and  ammonia ;  and  knowing 
the  proportions  of  oxygen,  hydrogen,  and  carbon,  which  they  re- 
spectively contain,  we  are  able  to  ascertain  the  precise  amount 
and  relative  proportion  qf  the  elements  which  entered  into  the 
constitution  of  the  substance  analysed. 

275.  The  general  result  of  the  investio-ations  which  have  been 
conducted  by  the  last  of  these  methods  is,  that  the  simple  bodies 
of  which  animal  substances  consist  are  comprised  in  the  following 
Hst: 

1.  Oxygen.  2.  Nitrogen.  3.  Carbon.  4.  Hydrogen.  5.  Lime. 
6.  Phosphorus.  7.  Sulphur.  8.  Soda.  9.  Potass.  10.  Chlorine. 
11.  Magnesia.     12.  Iron.     13.  Silica.     14.  Manganese. 

276.  Of  these,  the  first  six  may  be  considered  as  the  principal 
elementary  ingredients  of  animal  substances.  Magnesia  and 
Silica  are  found  only  in  very  minute  quantities,  and  may  there- 
fore be  in  a  great  measure  considered  as  foreign  bodies.  The 
soft  parts  of  the  body  are  composed  almost  entirely  of  oxygen, 
nitrogen,  carbon,  and  hydrogen  ;  while  lime  and  phosphorus  form 
the  basis  of  the  hard  parts. 

277.  The  proximate  principles  most  generally  met  with  in 
animal  substances  are.  1.  Gelatin.  2.  Albumen.  3.  Fibrin. 
4.  Mucus. 

278.  To  these  have  been  added  some  others,  such  as  urea, 
picromel,  stearin,  elain,  osmazone,  and  several  saccharine  and 
acid  principles,  which  being  more  limited  in  their  extent,  will 
fall  more  properly  under  consideration  in  the  review  we  shall 
give  of  the  substances  which  chiefly  contain  them.  We  shall 
first  then  present  an  account  of  the  properties  of  the  four  essen- 
tial principles  above  enumerated. 

4.   Gelatin. 

279.  Gelatin  may  be  extracted  by  long  continued  boiling  in 
water  from  almost  all  the  hard  and  solid  parts  of  the  body,  such 
as  the  skin,  membranes,  ligaments,  cartilages,  and  even  the  bones 
themselves.  By  the  slow  evaporation  of  the  water  which  thus 
holds  it  in  solution,  the  gelatin  may  be  obtained  in  a  state  of 
purity,  when  it  appears  as  a  hard,  brittle,  and  semi-transparent 
substance,  which  breaks  with  a  glassy  fracture.     It  varies  some- 


136  NUTRITIVE    FUNCTIONS. 

what  in  its  appearance,  according  to  the  source  from  which  it 
has  been  obtained.  Glue  may  be  taken  as  an  example  of  dried 
gelatin,  in  which,  however,  a  few  impurities  are  contained. 
Isinglass  may  be  considered,  on  the  whole,  as  the  purest  form 
under  which  gelatin  is  met  with,  and  it  exhibits  most  con)pletely 
the  characteristic  properties  of  that  proximate  animal  constituent. 

280.  One  of  the  most  striking  characteristics  of  gelatin  is  the 
property  it  exclusively  possesses,  when  united  to  a  quantity  of 
water,  of  dissolving  slowly,  but  completely,  forming  a  solution 
of  an  opaline  colour,  which  is  perfectly  fluid  when  warm,  but 
becomes  concrete  on  cooling,  assuming  the  tremulous  appear- 
ance so  well  known  as  belonging  to  jelly.  In  this  state  it  readily 
again  becomes  liquid,  by  the  application  of  a  gentle  heat,  and 
mav,  by  the  continuance  of  that  heat,  be  brought  back  to  the 
state  of  dryness.  These  alternate  solutions  and  d'esicca'tions  may 
be  repeated  for  any  number  of  times,  without  any  change  being 
produced  in  the  chemical  constitution  of  the  gelatin.  The  pro- 
portion in  which  gelatin  forms  a  solution  capable  of  concreting 
by  cooling,  has  been  ascertained  by  Dr.  Bostock  in  the  follow- 
ing manner.  One  part  of  dry  gelatin  to  100  parts  of  water  gave 
a  solution  which  completely  stiifened  by  cooling.  But  when  the 
proportion  of  water  was  150  parts  to  one  of  gelatin,  a  compound 
was  produced,  which,  though  evidently  gelatinous,  did  not  as- 
sume the  concrete  form. 

281.  Solid  gelatin  undergoes  no  change  if  it  be  kept  perfectly 
dry;  but  when  united  with  water,  either  in  the  form  of  solution 
or  of  jelly,  it  very  soon  becomes  putrid;  an  acid  first  makes  its 
appearance,  a  fetid  odour  arises,  and  ammonia  is  afterwards 
formed. 

282.  The  most  ready  and  convenient  test  of  the  presence  of 
gelatin  in  any  fluid  is  a  solution  of  tannin;  the  addition  of  which 
immediately  occasions,  by  the  combination  of  these  two  princi- 
ples, a  copious  precipitate,  which  assumes  a  solid  form.  This 
precipitate  collects  into  an  elastic  adhesive  mass,  which  soon 
dries  in  the  open  air,  and  forms  a  brittle  resinous-like  substance, 
very  similar  in  appearance  to  over-tanned  leather.  It  is  per- 
fectly insoluble  in  water,  and  is  not  susceptible  of  putrefaction. 
It  is  this  combination  of  tannin  with  gelatin  that  constitutes  the 
preservative  part  of  tanned  leather,  and  which  enables  it  to  re- 
sist the  transmission  of  moisture.  The  solutions  of  tannin  most 
conveniently  appKcable  as  tests  of  gelatin,  may  be  prepared  by 
an  infusion  of  an  ounce  of  gall-nuts  in  a  pint  of  water ;  or,  as 
Dr.  Bostock  has  proposed,  the  extract  of  rhatania,  digested  in 
hot  Vv^ater,  and  filtered  after  it  becomes  cold.  A  considerable 
precipitate  is  produced  by  these  infusions,  when  the  proportion 
of  gelatin  to  the  water  is  so  small  as  to  compose  only  the  five 
thousandth  part  of  the  solution.  The  precipitate  afforded  by 
tannin  is  not,  however,  to  be  considered  as  a  decisive  test  of  the 


PROXIMATE    ANIMAL    PRINCIPLES.  137 

presence  of  gelatin  ;  for,  as  we  shall  presently  find,  it  also  occurs 
in  consequence  of  the  presence  of  albumen.  In  order  to  pre- 
vent any  confusion  from  this  cause,  it  will  be  necessary  to  have 
recourse  also  to  another  test,  that  of  corrosive  sublimate,  which 
is  found  to  precipitate  albumen,  but  not  gelatin.  If,  therefore,  by 
adding  corrosive  sublimate,  we  obtain  no  precipitate,  we  may  be 
certain  of  the  presence  of  albumen. 

283.  Gelatin  is  insoluble  i»  alcohol,  but  when  already  in  solu- 
tion in  water,  it  is  not  precipitated  by  that  fluid.  Acids  dissolve 
it  with  great  facility,  even  when  much  diluted,  especially  when 
aided  by  heat.  The  nitric  acid  eftects  its  decomposition,  during 
which  nitrogen,  and  then  nitrous  gas,  are  disengaged  in  consider- 
able quantities ;  and  oxalic  and  malic  acids  are  evolved,  and 
may  be  obtained  from  the  residuum.  Sulphuric  acid,  with  the 
assistance  of  heat,  partly  converts  it  into  a  substance  resembling 
sugar.  Chlorine  combines  with  gelatin,  forming  a  white  sub- 
stance, which  assumes  the  form  of  filaments. 

The  pure  liquid  alkalies  dissolve  gelatin  very  readily.  The 
solution  is  a  brown  viscid  substance,  which  possesses  none  of  the 
properties  of  soap,  and  is  not  precipitated  by  acids.  This  pro- 
perty of  remaining  dissolved  after  acids  are  added  to  the  alkaline 
solution,  distinguishes  gelatin  from  albumen,  fibrin,  and  other 
animal  products,  and  is  therefore  a  valuable  mode  of  discrimi- 
nating its  presence,  and  of  separating  it  from  them  in  analysis. 

284.  Gelatin  is  precipitated  by  several  of  the  metallic  salts 
and  oxides,  but  not  so  unequivocally  as  to  aflx)rd  satisfactory 
tests  of  its  presence.  Like  all  the  other  constituents  of  animal 
bodies,  gelatin,  while  it  preserves  its  essential  properties,  is  sus- 
ceptible of  many  shades  of  variation,  and  appears  therefore 
under  a  diversity  of  forms,  such  as  glue,  size,  isinglass,  &c. ;  but 
although  many  valuable  remarks  on  this  subject  are  contained  in 
Mr.  Hatchett's  Observations  on  the  Component  Parts  of  Animal 
Membrane,  published  in  the  Philosophical  Transactions  for  1800, 
we  are  still  very  much  in  the  dark  as  to  the  circumstances  w^hich 
occasion  the  differences  in  the  several  kinds  of  animal  gelatin. 

5.  Albumen, 

285.  The  proximate  principle,  which,  from  its  composing  the 
greater  part  of  the  white  of  eg^,  has  been  termed  albumen,  is 
most  abundantly  met  with  in  almost  all  the  parts  of  animals, 
whether  solid  or  fluid.  It  is  the  chief  basis  of  several  of  the 
more  solid  textures  of  the  body,  such  as  the  membranous  and 
fibrous  structures,  and  the  parenchymatous  substance  of  the 
glands  and  viscera;  and  it  also  forms  a  large  proportion  of  the 
blood  and  of  the  secreted  fluids. 

In  the  white  of  egg,  albumen  exists  in  a  state  of  solution  in 

12* 


138  NUTRITIVE    FUNCTIONS. 

water,  and  combined  with  a  small  quantity  of  soda.  By  agita- 
tion with  a  still  larger  quantity  of  water,  the  two  fluids  unite,  and 
form  a  viscid  liquid,  the  component  parts  of  which  do  not  sepa- 
rate by  standing. 

286.  The  characteristic  property  of  albumen  is  its  capability 
of  coagulating,  or  passing  from  a  liquid  to  asohd  form,  by  the 
action  of  heat,  of  acids,  and  of  alcohol,  and  several  metallic 
salts  and  oxides.  This  change  tak^  place  in  undiluted  albumen, 
at  a  temperature  of  160°  Fahrenheit.  After  it  has  been  once 
coagulated,  albumen  is  no  longer  soluble  in  water,  unless  by  long 
boiling,  aided  by  pressure.  By  a  long  cojitinued  gentle  heat, 
CQagulated  albumen  gradually  has  its  moisture  dissipated,  and 
the  solid  matter,  amounting  to  about  one-fifth  of  the  original 
weight  is  left  behind,  in  the  form  of  a  hard  brittle  transparent 
substance. 

287.  If  the  albumen  be  much  diluted,  it  appears  to  be  incapa- 
ble of  coagulation  by  the  usual  means;  but  still  it  was  found  by 
Dr.  Bostock,  that  a  solution  containing  only  one  tjiousandth 
of  its  weight  of  albumen,  ahhough  not  properly  coagulated,  was 
rendered  perceptibly  opaque  by  a  boiling  temperature ;  so  that 
heat  may  be  considered,  for  all  practical  purposes,  as  a  suf- 
ficiently accurate  test  of  its  presence  in  any  fluid.  During  coagu- 
lation there  is  no  absorption  of  oxygen;  nor  is  any  gas  extricated: 
and  hence  there  appears  to  be  no  reaction  of  the  principles  of  the 
albumen  upon  each  other.  The  nature  of  the  change,  which 
takes  place  during  this  transition  from  the  fluid  to  the  solid  form, 
is  by  no  means  well  ascertained.  Dr.  Thomson  supposed  the 
fluidity  of  albumen  to  depend  on  the  presence  of  alkaline  matter; 
and  its  coagulation  to  the  removal  or  neutralization  of  this  alkali; 
and  some  experiments  which  were  devised  by  Mr.  Brande  tend 
strongly  to  support  this  theory.  He  found  that  a  rapid  and  abun- 
dant coagulation  took  place  in  the  white  of  an  egg  subjected  to 
the  action  of  a  galvanic  battery,  around  the  negative  pole,  where 
the  alkah  must  have  been  separated  ;  while  a  thin  film  only  col- 
lected round  the  positive  pole.  He  discovered  also,  by  these 
experiments,  that  galvanic  electricity  may  be  applied  succes- 
sively to  the  detection  of  very  minute  quantities  of  albumen, 
which  would  not  be  rendered  sensible  by  any  other  test. 

288.  Another  agent  which  immediately  effects  the  coagulation 
of  albumen,  unless  it  be  previously  much  diluted,  is  alcohol. 
Ether  also  produces  the  same  effect. 

289.  Acids  in  general  occasion  the  coagulation  of  albumen; 
but  several  of  them  afterwards  redissolve  the  coagulum  if  assisted 
by  heat.  This  is  at  lea»t  the  case  with  the  three  mineral  acids. 
The  coagulum  formed  by  acids  always  retains  in  combination  a 
portion  of  the  acid  which  has  been  employed.  That  produced 
by  nitric  acid  is  the  least  soluble;  and  hence  nitric  acid  occa- 


PROXIMATE    ANIMAL    PRINCIPLES.  139 

sions  a  precipitate  from  solutions  of  albumen,  which  are  so  dilute 
as  not  to  bo  affected  by  other  acids.  Thenard  remarks  that  the 
coagulum  produced  by  acids,  is  re-dissolved  by  pure  alkalies, 
and  even  by  ammonia,  which  does  not  dissolve  albumen  that  has 
been  coagulated  by  heat.  ]\itric  acid,  when  concentrated,  de- 
composes albumen,  extricating  from  it  azotic  gas,  and  during  its 
solution,  nitrous  gas.  Oxalic  and  malic  acids  are  formed,  and  a 
thick  oily  matter,  soluble  in  alcohol,  appears  on  the  surface.  On 
the  other  hand,  when  coagulated  albumen  is  subjected  to  the 
action  of  dilute  nitric  acid,  it  is  after  some  time  converted  into  a 
substance  having  the  properties  of  gelatin.  For  this  highly  curious 
fact  we  are  indebted  to  Mr.  Hatchett.*  Alum,  probably  in  con- 
sequence of  its  excess  of  acid,  coagulates  albumen,  provided  the 
solution  be  not  very  dilute.  One  part  of  albumen  in  five  hundred 
of  water  is  rendered  slightly  turbid  by  a  solution  of  alum,  but 
without  any  formation  of  a  precipitate. 

290.  The  triple  prussiate  or  ferrocyanate  of  potass  is,  accord- 
ing to  Dr.  Henry,  an  extreinel}^  delicate  test  of  the  presence  of 
albumen,  and  may  be  used  to  discover  it  in  fluids  to  which  other 
tests  are  inapphcable.  To  enable  it,  however,  to  produce  a  pre- 
cipitate, a  very  shght  excess  of  acetic  acid  should  be  previously 
added,  either  to  the  test,  or  to  the  hquid  suspected  to  contain 
albumen. 

291.  Another  dehcate  test  of  the  presence  of  albumen  is  a 
solution  of  corrosive  sublimate ;  and  it  is  the  more  valuable, 
inasmuch  as  it  has  no  effect  on  solutions  either  of  gelatin  or  of 
mucus.  Dr.  Bostock  found  that  a  single  drop  of  a  solution  of 
corrosive  subhmate,  added  to  a  hquor  containing  one-thousandth 
of  its  weight  of  albumen,  renders  it  visibly  mdky,  and  at  the  end 
of  some  hours  a  flocculent  precipitate  falls  to  the  bottom  of  the 
vessel.  The  same  re-agent  produces  a  sensible  effect  on  a  liquid, 
containing  only  half  that  quantity,  or  one  two-hundredth  of  albu- 
m.en. 

292.  Many  other  metallic  sahs,  throw  down  a  precipitate  from 
solutions  of  albumen, — as  the  acetate  of  lead,  the  nitro-muriate 
of  tin,  the  nitrate  of  silver,  and  the  nitro-muriate  of  gold  ;  but  as 
they  produce  a  similar  effect  on  other  species  of  animal  matter, 
they  are  scarcely  deserving  of  confidence  as  tests  of  any  one  in 
particular.     A  solution  of  tannin,  which,  when  added  to  albumen, 

»  occasions,  after  some  time,  a  precipitate,  may  sometimes  afibrd 
useful  indications  in  analytical  inquiries,  for  it  may  be  distinguished 
from  that  produced  from  gelatin  by  its  want  of  density,  and 
cohesion. 

293.  Albumen  is  readily  dissolved  by  the  pure  liquid  alkalies, 
which  disengage  ammonia  from  it,  and  form  with  the  residue  a 

*  See  his  paper  already  quoted  from  the  F hilosophical  Transactions  fox 
1800. 


140  NUTRITIVE    FUNCTIONS. 

saponaceous  compound.  *  This  soap,  when  dissolved  in  water,  is 
precipitated  by  acetic  or  muriatic  acids. 

6.  Fibrin. 

294.  The  proximate  animal  principle,  known  by  the  name  of 
fibrin,  or  animal  gelatin,  eid'&is  in  large  quantity  in  the  blood,  and 
forms  the  basis  of  the  muscular  flesh  of  animals.  When  properly 
prepared,  and  freed  from  the  admixture  of  extraneous  matter,  it 
presents  a  substance  of  a  white  colour,  destitute  of  taste  or  smell, 
of  a  fibrous  texture,  and  of  a  soft  and  elastic  consistence.  When 
dried  it-  is  brittle,  and  has  a  certain  degree  of  transparency ;  it 
undergoes  no  change  from  the  action  of  either  air  or  water. 

295.  When  exposed  to  heat,  it  contracts  very  considerably, 
and  exhibits  movements  like  horn,  exhaling  at  the  same  time  the 
smell  of  burned  feathers.  When  subjected  to  great  heat,  it  yields 
the  usual  animal  products  of  water,  oil,  ammonia,  carbonic  acid, 
and  carburetted  hydrogen,  with  a  large  carbonaceous  residuum. 
This  charcoal  is  very  difHcult  to  incinerate,  owning  to  the  presence 
of  phosphoric  salts,  which  are  fused  by  the  heat  employed  for 
that  purpose,  and  form  a  glassy  coat  on  the  surface.  A  consider- 
able quantity  of  carbonate  of  Ume  is  found  in  the  residual  ashes. 

296.  The  acids  exert  a  considerable  action  upon  fibrin.  Con- 
centrated acetic  acid  renders  it  soft  and  transparent ;  and  the 
whole  mass  is  converted  by  heat  into  a  tremulous  jelly.  By  the 
addition  of  water,  and  the  continued  application  of  heat,  a  complete 
solution  is  effected,  attended  with  the  evolution  of  nitrogen.  Fibrin 
combines  with  muriatic  acid  in  two  proportions;  the  one  gives  a 
neutral  compound  soluble  in  water;  the  other,  containing  an  excess 
of  acid,  is  insoluble,  but  becomes  soluble  by  the  action  of  pure 
water.  Concentrated  sulphurjc  acid  decomposes  and  carbonizes 
fibrin.  Diluted  with  six  times  its  weight  of  water,  this  acid  ac- 
quires a  red  colour  by  being  digested  with  fibrin,  but  scarcely 
dissolves  any  sensible  portion  ;  but  part  of  the  acid  is  absorbed 
by  the  remaining  mass,.which  becomes  a  compound  of  fibrin  and 
an  excess  of  sulphuric  acid.  Water  deprives  it  of  this  excess, 
and  a  neutral  combination  is  obtained,  which  is  soluble  in  water, 
and  has  the  same  characters  as  neutral  muriate  of  fibrin.  The 
action  of  nitric  acid  upon  fibrin  is  much  diversified,  according  to 
its  dilution  or  state  of  concentration.  When  the  acid  is  diluted  ' 
with  a  large  quantity  of  water,  a  great  abundance  of  nitrogen 
gas  is  disengaged.  This  gas  is  entirely  derived  from  the  fibrin, 
and  not  from  the  acid,  which,  as  Berthollet  ascertained,  has  suf- 
fered no  decomposition  during  the  process.  The  residuum,  in 
this,  case,  is  principally  oxalic  acid,  with  a  small  quantity  of 
malic  and  acetic  acids,  and  a  portion  of  fatty  matter.  When 
the  nitric  acid  is  undiluted,  on  the  other  hand,  it  undergoes  de- 


PROXIMATE    ANIMAL    PRINCIPLES.  141 

composition,  and  nitrous  gas,  mixed  witli  nitrogen  gas,  is  dis- 
engaged. When  fibrin  is  digested  for  twenty-four  hours  in  nitric 
acid  of  the  specific  gravity  1.25,  it  is  converted  into  a  pulverulent 
mass,  of  a  pale  citron  colour,  which  is  deposited  at  the  bottom 
of  the  liquid.  By  washi-ng  it  in  water,  the  excess  of  acid  is 
carried  otf',  and  the  colour  gradually  becomes  of  a  deep  orange. 
Fourcro}'-  and  Vau(iuelin  considered  this  yellow  matter  to  be  a 
peculiar  acid,  which  they  distinguished  by  the  name  of  the  yellow 
acid.  But  Berzelius  has  shown  that  it  is  merely  fibrin  combined 
with  nitric  and  malic  acids.  When  the  action  of  nitric  acid  on 
fibrin  is  very  slow,  it  is  gradually  converted  into  a  state  somewhat 
analogous  to  gelatin. 

297.  Fibrin,  when  subjected  to  the  action  of  caustic  alkali,  in- 
creases in  bulk,  becomes  transparent  and  gelatinous,  and  at  length 
is  entirely  dissolved,  forming  a  yellowish  green  solution.  From 
this  solution  it  is  precipitated  both  by  acids  and  alcohol,  but  seems 
to  have  undergone  some  change  ;  for  it  is  not,  as  before,  soluble 
in  acetic  acid.  Fourcroy  had  asserted,  that  the  compound  of 
fibrin  and  alkali  resembles  soap ;  but  it  does  not,  in  fact,  appear 
to  have  any  analogy  with  saponaceous  bodies. 

298.  Alcohol  of  the  specific  gravity  of  0.81,  converts  fibrin  into 
a  kind  of  adipocirous  matter,  which  is  soluble  in  alcohol,  and 
precipitated  by  the  addition  of  water.  It  has  a  strong  and  un- 
pleasant odour.  The  alcoholic  solution  leaves,  on  evaporation, 
a  fatty  residue,  which  did  not  pre-exist  in  the  fibrin,  but  which, 
like  the  origio^al  substance,  is  soluble  in  acetic  acid.  By  the 
action  of  ether,  fibrin  is  converted  into  the  same  kind  of  adipocire, 
but  which  has  a  more  ofl^ensive  odour,  and  is  in  larger  quantity. 

299.  After  the  account  we  have  given  of  the  three  proximate 
principles  which  enter  so  largely  into  the  composition  of  animal 
matter,  namely,  gelatin,  albumen,  and  fibrin,  it  will  be  useful  to 
take  a  comparative  view  of  the  analogies  they  present,  and  of 
the  differences  by  which  they  are  distinguished,  both  in  their 
properties  and  composition.  ,They  are  apparently  composed  of 
the  same  ultimate  elements,  combined  in  proportions  which  are 
not  widely  different.  They  admit  accordingly  of  mutual  con- 
version into  one  another,  by  processes  which  produce  a  slight 
alteration  in  the  proportion  of  their  constituents.  By  the  action 
of  the  nitric  acid,  fibrin  is  converted  into  a  kind  of  gelatin,  and  a 
similar  change  has  been  effected  on  albumen  by  the  same  re- 
agent. All  these  substances  are  presented  both  in  the  liquid  and 
sfJid  forms,  and  pass  readil}'-  from  the  former  to  the  latter  of 
these  states,  without  any  apparent  change  in  their  chemical 
constitution.  They  are  all  of  them  indestructible  when  perfectly 
dry,  but  readily  undergo  putrefaction  when  united  with  water. 
Yet  the  modes  in  which  they  are  respectively  acted  upon  by 
water  are  different,  and  this  affords  an  easy  character  of  distinc- 


142  NUTRITIVE    FUNCTIONS. 

tion  bjetween  them.  Gelatin  is  soluble  in  cold  water  ;  the  solu- 
tion when  evaporated  becomes  gelatinous ;  and  if  this  jelly  be 
dried,  it  is  still  again  soluble.  Albumen  is  likewise  soluble  in 
water;  but  whenever  the  temperature  is  raised  to  170°,  it  sepa- 
rates by  coagulation,  and  this  coagulum  is  not  again  soluble. 
Fibrin  is  clearly  distinguished  by  its  total  insolubility  in  water  at 
any  temperature,  at  least  under  the  common  atmospheric  pres- 
sure. 

300.  Then  these  principles  likewise  differ  in  their  composition ; 
for  though  they  seem  to  consist  of  the  same  ultimate  princi- 
ples,—  nitrogen,  hydrogen,  oxygen,  carbon,  phosphorus,  and 
sulphur,  yet  these  differ  somewhat  in  their  proportions.  The 
most  accurate  analysis  of  these  substances  into  their  ultimate 
elements,  are  those  of  MM.  Gay  ]jussac  and  Thenard,  the  results 
of  which  are  exhibited  in  the  following  table  : 

Gelatin.  Albumen.  Fibrin. 

Carbon,     -     -     -     47-881  -  52-883  -  53-360 

Oxygen,    -     -     -     27-207  -  23-872  -  19-685 

Nitrogen,-     -     -     16-988  -  15-705  -  19-934 

Hydrogen,     -     -       7-914  -  7-540  -  7-021 


100.  100.  100. 

It  appears  from  the  above  analysis,  that  the  principal  difference 
of  composition  occurs  in  the  proportion  of  nitrogen.  Gelatin 
contains  the  least  of  this  element ;  albumen  more  ;  and  fibrin  a 
quantity  considerably  larger  than  either  of  the  others.  The  last 
substance  appears  therefore  to  be  the  most  animalized  product. 
It  also  contains  the  largest  quantity  of  carbon,  as  appears  indeed 
from  the  greater  residuum  of  charcoal,  which  it  leaves  after 
destructive  distillation.  Sulphur  is  perhaps  peculiar  to  the  com- 
position of  albumen.  On  the  other  hand,  the  proportion  of  oxygen 
is  considerably  greater  in  gelatin  than  in  either  of  the  other  two 
substances.  This  predominance  of  oxygen,  together  with  the 
less  compactness  of  its  mechanical  composition,  are  probably  the 
causes  of  the  greater  tendency  which  gelatin  shows  to  pass  into 
the  acid  fermentation.  In  this  respect,  also,  gelatin  shows  itself 
to  be  less  completely  animalized  than  the  other  proximate  prin- 
ciples, and  to  partake  more  of  the  chemical  character  of  vegeta- 
ble substances,  which  are  well  known  to  evolve  an  acid  in  the 
progress  of  spontaneous  decomposition.  There  are  indeed  some 
vegetables,  as  the  tribe  of  fungi,  that  become  alkaline  by  their 
putrescence ;  and  these  are  found  to  contain  nitrogen ;  so  that 
gelatin  on  the  one  hand,  and  the  fungi  on  the  other,  may  be 
regarded  as  forming,  on  each  side,  the  connecting  links  between 
these  two  great  kingdoms  of  nature. 

301.  It  is  a  curious  subject  of  speculation  to  reduce  the  pro- 


PROXIMATE    ANIMAL    PRINCIPLES.  143 

portions  resulting  from  tlie  analysis  of  the  French  chemists,  to 
those  which  are  most  reconcileable  to  the  atomic  theory.  They 
will  then  stand  as  follows ; 


Number  of  atoms  of 

In  Gelatin. 

In  Albumen. 

In  Fibrin. 

Carbon, 

- 

15 

- 

17       - 

-        18 

Oxygen,     - 

-       - 

6 

,.     - 

6       - 

5 

Nitrogen,  - 

- 

2 

- 

2       - 

3 

Hydrogen,'; 

-       - 

14 

-     - 

13       - 

-      14 

The  weights,  both  absolute 

1  an 

d  relative,  of  the  atomic  elements, 

are  shown  in  the  foll( 

awing  table : 

Gelatin. 

Albi 

imen. 

Fibrin. 

Absolute. 

Relative. 

Absolute. 

Relative.  , 

Absolute. 

Relative. 

Carbon,    -    -    90    - 

50-00 

- 

102    - 

53-40  .- 

108    - 

52-94 

Oxygen,  -    -    48    - 

26-67 

. 

48    - 

25-13    - 

40    - 

19-61 

Nitrogen,-    -    28    - 

15-55 

- 

28    - 

14-67     - 

42    - 

20-59 

Hydrogen    -    14    - 

7-78 

- 

13    - 

6-80     - 

14    - 

6-86 

180       100-  191       100-  204       100- 

In  the  conversion  of  albumen  into  jelly,  by  the  slowly  continued 
action  of  nitric  acid,  we  may  conclude  that  the  acid  imparts  a 
portion  of  its  oxygen  to  the  albumen,  and  perhaps  adds  also  a 
small  quantity  of  nitrogen ;  thus  constituting  the  proportions 
assigned  to  gelatin  by  Gay  Lussac  and  Thenard. 

7.  Mucus. 

302.  The  term  mucus  has  been  employed  in  very  different 
senses  by  different  writers.  Some  have  applied  it  vaguely  to  al- 
most every  animal  substance  which  was  not  referable  to  any  other 
class.  Fourcroy  and  Vauquelin,  while  they  include  under  this 
term  the  viscid  secretions  which  lubricate  the  alimentary  and 
other  passages  that  open  at  the  surface  of  the  body,  have  admit- 
ted its  claim  to  be  considered  as  a  peculiar  proximate  principle, 
but  regard  it  as  analogous  to  vegetable  gum,  from  which  they 
suppose  it  to  differ  only  by  containing  a  portion  of  nitrogen.  Their 
descriptive  account  of  its  properties,  however,  is  deficient  in  the 
precision  which  the  subject  seems  to  require,  and  which  has  been 
aimed  at  by  subsequent  chemists.  Berzelius,  it  is  true,  refuses 
to  allow,  that  there  is  any  such  common  principle  as  mucus, 
and  founds  his  opinion  on  the  ground  that  the  chemical  characters 
of  the  fluids,  which  bear  that  name,  are  very  various  in  different 
parts  of  the  body,  and  are  modified  in  different  situations,  ac- 
cording to  the  particular  purposes  they  are  intended  to  fulfil. 
Mr.  Hatchett,  in  his  interesting  paper  on  the  Component  Parts  of 
Animal  Memhrane,  has  attempted  to  fix  the  meaning  of  the  term 
more  definitely.     Viewing  mucus  as  extremely  analogous  in  its 


144  NUTRITIVE    FUNCTIONS.  ' 

properties  to  gelatin,  he  considers  these  two  substances  as  mere- 
ly naodifications  of  each  other;  the  former  characterized  by  its 
incapability  of  being  gelatinized ;  the  latter  by  possessing  that 
property ;  while  both  are  soluble  in  water. 

Dr.  Bostock.  in  his  excellent  papers  on  the  Analysis  of  Animal 
Fluids,  has  endeavoured  to  establish  definite  characters  as  belong- 
ing to  this  fluid,  when  existing  in  a  state  of  purity.  He  states, 
that  if  the  solid  matter,  obtained  from  the  evaporation  of  saliva 
to  dryness,  be  re-dissolved  in  water,  and  filtered,  the  solution  will 
consist  of  mucus  alone,  or  with  scarcely  any  extraneous  sub- 
stance. ^Y  a  careful  evaporation  he  found  that  the  solution 
contained  one  two-hundredth  part  of  its  weight  of  mucus.  He 
also  obtained  a  similar  principle  by  macerating  an  oyster  in 
water,  and  evaporating  the  liquid.  It  thus  appeared  that  the  water 
had  dissolved  about  one-fiftieth  of  its  weight  of  animal  matter. 
Mucus  thus  obtained  resembles  gum-arabic,  excepting  that  it  is 
somewhat  more  opaque.  Like  it,  it  has  scarcely  any  taste,  dis- 
solves readily  in  water,  and  forms  an  adhesive  solution.  Alcohol 
added  to  this  solution  has  no  tendency  to  coagulate  it.  No  ap- 
pearance of  coagulation  is  produced  by  exposing  the  fluid  for 
some  time  to  the  heat  of  boiling  water  ;  nor  is  there  any  tendency 
to  gelatinize,  by  evaporating  and  afterwards  cooling  the  fluid. 
No  distinct  effect  is  produced  on  the  solution  of  mucus,  either  by 
the  nitro-muriate  of  tin,  corrosive  sublimate,  or  the  infusion  of 
galls.  The  subacetate  of  lead,  or  Goulard's  extract,  occasions ' 
an  immediate  opacity,  and,  after  some  time,  a  flaky  precipitate. 
'  303.  Dr.  Bostock  concludes  that  a  decided  and  essential  dif- 
ference is  thus  established  between  mucus  and  jelly,  by  the 
different  effects  produced  by  tannin,  and  by  subacetate  of  lead. 
Tannin  is  a  most  delicate  test  of  jelly,  but  does  not  in  any  degree 
affect  mucus.  Goulard's  extract,  on  the  other  hand,  is  a  dehcate 
test  of  mucus,  but  does  not  in  any  degree  aflTect  jelly.  The  bi- 
chloride of  mercury  (corrosive  sublimate),  on  the  contrary,  which 
is  one  of  the  most  accurate  tests  of  albumen,  does  not  appear  to 
affect  either  jelly  or  mucus. 

Notwithstanding  the  attempts,  which  Dr.  Bostock  made  to  de- 
vise a  method  of  directly  determining  the  proportion  of  mucus 
in  a  compound  fluid,  he  was  not  able  to  succeed,  in  consequence 
of  the  facility  with  which  Goulard's  solution  decomposes  the  dif- 
ferent extraneous  ingredients,  both  animal  and  saline,  which  are 
almost  always  present  in  substances  that  contain  mucus,  even  in 
a  state  the  nearest  approaching  to  purity.  The  salts  are  particu- 
larly liable  to  act  upon  the  metallic  solutions  employed  as  tests; 
so  that  it  is  impossible  to  say  how  much  of  the  effect  is  owing  to 
each  of  these  separate  causes.  The  precipitates  thrown  down 
from  mucus  by  subacetate  of  lead,  and  nitrate  of  silver,  were 
found  by  Mr.  Brande  to  consist  both  of  the  muriates  and  phos- 


FUNCTIONS    OF    ASSIMILATION.  145 

phates  of  those  metals.  Mr.  Brande  also  attempted  to  obtain 
mucus  free  from  neutral  salts,  by  subjecting  it  to  the  action  of 
galvanic  electricity.  He  thus  detected  a  small  quantity  of  al- 
bumen in  saliva,  which  was  not  discoverable  by  the  ordinary 
tests. 

304.  A  great  resemblance  has  frequently  been  noticed  between 
the  mechanical  properties  of  animal  mucus  and  vegetable  gum  ; 
and  Dr.  Bostock  found  that  they  strongly  resemble  each  other 
also  in  their  chemical  qualities.  A  solution  of  gum-arabic,  con- 
taining one  grain  of  gum  or  two  hundred  grains  of  water,  was 
not  affected  either  by  the  bichloride  of  mercury,  or  by  tannin. 
With  the  nitro-muriate  of  tin,  and  with  the  nitrate  of  silver,  there 
was  only  a  slight  degree  of  opacity ;  but  with  the  subacetate  of 
lead  there  was  a  dense  precipitate  instantly  formed. 

305.  On  the  whole,  however,  animal  mucus  in  its  chemical 
relations  appears  to  be  most  nearly  allied  to  albumen ;  and  the 
constituent  upon  which  its  characteristic  properties  principally 
depend,  would  seem,  as  Dr.  Bostock  remarks,  be  a  mere  modifi- 
cation of  this  substance. 

306.  We  shall  conclude  our  account  of  this  substance  by  the 
following  direction  as  to  the  order  in  which  it  will  be  most  con- 
venient to  conduct  our  analytical  inquiries  of  a  fluid,  which  may 
be  supposed  to  contain  either  albumen,  jelly,  or  mucus.  The 
first  step  is  to  observe  the  effect  of  the  bichloride  of  mercury ;  if 
this  produce  no  precipitate,  we  may  be  certain  that  the  fluid  in 
question  contains  no  albumen.  We  should  next  employ  the  in- 
fusion of  galls,  and  if  this  also  occasion  no  precipitate,  we  may 
conclude  that  the  animal  matter  held  in  solution  consists  of  mucus 
alone.  Such  being  the  chemical  properties  of  the  chief  proximate 
principles  of  animal  organization,  we  have  next  to  examine  the 
mode  in  which  these  substances  are  produced  in  the  economy. 

Sect.  II. — Arrangement  of  the  Functions  of  Assimilation. 

307.  The  means  provided  by  nature  for  meeting  the  various 
demands  of  the  system,  by  converting  materials  derived  from 
without  into  the  proximate  principles  of  animal  organization,  the 
properties  of  which  we  have  now  examined,  constitute  a  separate 
class  of  functions  distinct  from  all  the  others.  They  might  not 
unaptly  be  termed  the  reparatory  functions ;  but  as  the  changes 
which  are  effected  in  the  materials  receiv^ed  into  the  body  ibr  its 
conversion  into  nutriment  are  wdiolly  of  a  chemical  nature,  we 
thought  they  might,  with  still  greater  p^ropriety,  be  termed  the 
chemical  functions,  in  contradistinction  to  those  the  objects  of 
which  are  entirely  of  a  mechanical  nature,  and  which  have  already 
passed  under  our  review. 

308.  The  reparatory,  or  chemical  functions,  may  be  divided 

13 


l46  KtTRITlVE    PtlNCTIONS. 

into  two  great  orders  ;  the  first  consisting  of  those  -which  effect 
all  the  changes  that  the  food  undergoes  during  its  conversion  into 
blood  ;  the  second,  of  those  which  apply  the  blood,  or  nutriment 
thus  properly  prepared,  to  the  various  purposes  for  which  it  is 
wanted,  and  which  effect  in  it  those  chemical  changes  that  are 
required  for  those  objects. 

309.  The  first  order  may  again  be  subdivided  into  several 
subordinate  processes,  including,  1st,  the  preparation  which  the 
food  undergoes  in  the  mouth  by  mastication,  or  mechanical  divi- 
sion. 2d,  Its  admixture  with  saliva  and  other  secretions,  which 
is  generally  termed  in  salivation.  3d,  Its  deglutition,  or  convey- 
ance into  the  stomach.  4th,  Its  digestion  in  that  cavity,  and 
conversion  into  chyme,  which  may  properly  be  termed  c/iymifi- 
cation.  .5th,  The  subsequent  changes  it  undergoes  in  the  intes- 
tines, by  the  influence  of  various  agents,  such  as  the  bile,  the 
pancreatic  and  intestinal  secretions ;  and  its  ultimate  conversion 
into  chyle,  and  separation  from  the  excrementitious  portion, 
comprising  the  process  of  chylijication.  6th,  Its  absorption  by  the 
lacteals,  its  transmission  to  the  heart,  and  its  sanguification,  or 
conversion  into  blood.  To  the  above  functions  the  title  of 
natural  functions  was  given  by  the  older  physiologists,  and  the 
name  is  retained  in  many  modern  works  in  medicine. 

310.  The  second  order  comprehends,  in  like  manner,  a  number 
of  most  importatit  functions,  which,  from  their  immediate  influ- 
ence on  the  continuance  of  life,  have  been  emphatically  denomi- 
nated the  tj/te/ /Mwci!w??s.  They  consist,  1st,  of  the  Circulation 
of  the  blood,  by  means  of  the  heart,  arteries,  veins,  and  capillary 
vessels.  2d,  Bespiration,  by  which  every  portion  of  the  blood  is 
subjected  in  its  turn  to  the  chemical  action  of  the  air  respired ;  is 
freed  from  its  excess  of  carbon,  an-d  becomes  oxygenated,  or 
arterialized,  and  fit  to  be  applied  to  the  purposes  of  the  system. 
3d,  Secretion,  a  term  which  expresses  a  variety  of  changes  effected 
in  the  blood,  by  passing  through  glands  and  other  secreting  or- 
gans, adapting  it  to  different  purposes  in  different  cases.  Closely 
allied  in  its  object  to  secretion  is  the  function  of  (4th)  Nutrition, 
whereby  the  several  parts  of  the  body  receive  accessions  to  their 
growth,  and  are  maintained  in  the  condition  requisite  for  the 
perfect  performance  of  their  requisite  offices.  5th,  Absorption 
by  the  lymphatics,  for  the  removal  of  all  superfluous  or  decayed 
particles  in  the  body.  6th,  The  last  function  in  this  order,  which 
completes  the  series  of  chemical  changes  going  on  in  the  living 
laboratory  of  the  body,  is  Excretion,  or  the  separation  of  useless 
or  noxious  materials  from  the  blood,  and  their  rejection  from  the 
system.  We  shall  proceed  to  the  consideration  of  these  func- 
tions in  the  order  in  which  they  have  been  enumerated.  But  for 
the  proper  understanding  of  the  subjects  they  involve,  it  will  be 


PROPERTIES    OF    FOOD.  147 

necessary  to  premise  an  inquiry  into  the  chemical  nature  of  the 
substances  which  are  received  into  the  body  as'-food. 


Sect.  III. — Properties  of  Food. 

311.  The  food  of  man  is  more  various  in  its  kind  than  that  of 
any  other  animal;  for  it  comprehends  a  great  multitude  of  arti- 
cles both  of  animal  and  vegetable  nature.  Hence  man  has  been 
regarded  as  entitled  to  the  appellation  oi"  an  omnivorous  animal. 
His  powers  of  digestion,  however,  though  capable  of  being  exer- 
cised upon  a  great  variety  of  materials,  are  yet  inadequate  to  the 
assimilation  of  many  substances,  wh^ch  form  the  exclusive  food 
of  several  of  the  larger  quadrupeds  whose  structure  and  economy 
are  not  very  remote  from  those  of  man.  The  human  stomach 
and  intestines  are  incapable  of  extracting  nourishment  from  the 
fibrous  or  membranous  parts  of  vegetables,  like  the  ox,  the  sheep, 
and  other  herbivorous  animals;  nor  have  they  the  power  of 
digesting  hard  and  solid  bones,  like  the  hyasna,  the  dog,  and 
other  highly  carnivorous  quadrupeds.  Neither  the  leaves  of 
trees  nor  the  grasses,  have  ever,  in  any  age  or  country,  been 
used  as  the  food  of  man.  Many  savage  races  of  the  American 
continent,  though  possessing  vast  tracts  of  country  abounding  in 
trees  and  grass,  have  frequently  been  visited  by  the  extremes  of 
famine,  by  which  whole  districts  have  been  depopulated.  When 
Australia  was  first  visited  by  Europeans,  the  native  inhabitants 
were  found  only  occupying  the  sea-coast,  gathering  up  a  scanty 
and  precarious  subsistence  from  the  shell-fish  casually  thrown 
upon  the  shore ;  but  the  settlements  which  have  since  been  made 
have  occasioned  their  retirement  into  the  interior,  and  their 
numbers  have  rapidly  diminished.  It  is  obvious  that,  had  the 
leaves  of  the  vegetables  which  grow  wild  in  those  regions  been 
capable  of  affording  the  sniallest  sustenance,  they  would  have 
necessarily  been  resorted  to  in  these  extremities  of  hunger.  But 
no  authenticated  instance  of  the  kind  occurs  in  the  history  of  the 
human  race. 

312.  Man,  however,  seems  to  enjoy  the  exclusive  privilege  of 
having  organs  of  digestion  equally  adapted  to  the  assimilation  of 
both  animal  and  vegetable  aliment  of  certain  kinds;  and  the  range 
which  is  allowed  him  in  this  respect  is  most  extensive.  Hence 
we  find,  that  in  most  countries  where  there  prevails  a  high  degree 
of  civilization,  and  where  religious  scruples  do  not  interfere,  both 
animal  and  vegetable  food  is  indiscriminately  employed  by  all 
who  can  procure  them.  In  many  parts  of  the  globe,  indeed, 
necessity  compels  a  restriction  to  certain  kinds  of  diet;  and  in 
some  the  same  restriction  is  imposed  as  a  religious  duty.  Thus 
the  Gentoos  live  entirely  on  the  vegetable  produce  of  the  earth, 


148  NUTRITIVE    FUNCTIONS. 

to  which,  however,  they  add  the i highly  nutritious  article  of  milk. 
The  Birmans,  who  are  a  remarkably  active  and  robust  race,  are 
said  to  Hve  exclusively  upon  vegetable  food.  On  the  other  hand, 
the  inhabitants  of  the  mouths  of  many  of  the  African  rivers,  live 
wholly  upon  the  produce  of  the  ocean.  The  flesh  of  the  rein-deer 
constitutes  the  principal  food  of  the  Laplander.  In  general  it 
would  appear  that  the  inhabitants  of  cold  climates  consume  a 
larger  proportion  of  animal  food  than  those  of  the  torrid  zone- 
Whence  it  has  been,  with  much  probability,  inferred,  that  less 
combustible  matter  is  required  by  the  system  in  situations  where 
the  external  temperature  is  habitually  high  ;  a  remark  which,  if 
well  founded,  is  conformable  to  the  principle  already  laid  down 
in  our  statement  of  the  purposes  to  which  a  portion  of  the  food  is 
applied,  namely,  that  of  keeping  up  the  animal  temperature.  In 
the  ruder  periods  of  society,  when  the  arts  of  civilization  had  not 
yet  diffused  their  beneticial  inflqence  over  mankind,  it  is  probable 
that  men  were  more  carnivorous  than  in  the  present  state  of  the 
world.  The  introduction  of  the  use  of  corn,  and  other  grains 
of  the  same  class,  has  effected  in  this  respect  an  important  change 
in  the  condition  of  the  species ;  but  it  would  appear  that  the 
introduction  of  this  great  benefit  was  very  gradual,  and  must 
have  required  a  long  succession  of  ages  before  the  cultivation  of 
the  gramina  had  attained  any  degree  of  perfection. 

1.  Animal  Food: 

313.  The  parts  of  animals  which  is  chiefly  consumed  as  food 
is  the  muscular  flesh;  but  milk,  and  the  different  products  ob- 
tained from  milk,  together  with  eggs,  also  compose  articles  of 
diet.  The  animals  from  which  these  aliments  are  derived,  are 
principally  the  herbivorous  mammalia,  different  tribes  of  birds 
and  fish,  a  small  number  of  the  class  of  reptiles,  and  several 
species  of  raollusca  and  Crustacea.  The  flesh  of  the  mammalia 
and  of  birds  consists  principally  of  fibrin  and  gelatin,  intermixed 
also  with  fat.  Milk  may  be  considered  as  an  emulsion  of  albu- 
men, oil,  and  sugar,  suspended  in  a  large  quantity  of  water. 
The  two  former  ingredients,  when  obtained  separately,  constitute 
respectively  cheese  and  butter.  The  eggs  of  birds  chiefly  contain 
albumen,  together  with  a  smaU  quantity  of  oil.  Fish  contains 
less  fibrin,  but  a  larger  portion  of  albumen  and  gelatin  than  the 
flesh- of  either  quadrupeds  or  birds;  and  in  some  fish  there  is 
joined  to  these  constituents  a  large;  quantity  of  oil.  This  also  is 
the  case  with  those  Crustacea  and  moUusca  which  are  used  as 
articles  of  diet.  When  we  come,  therefore,  to  analyze  the 
proximate  principles  from  which  animal  nutriment  is  derived, 
we  find  them  reducible  to  the  following:  namely,  fibrin,  albumen. 


PROPERTIES    OF    FOOD.  149 

oil,  gelatin,  and  sugar;  together  with  a  few  others,  such  as 
ozmazome,  M'hich  are  of  minor  importance. 

2.   Vegetable  Food. 

314.  The  parts  of  vegetables  most  frequently  consumed  as 
food,  are  the  seeds,  seed-vessels,  fruits,  stalks,  .roots,  and  tubera, 
and  more  commonly  the  leaves.  The  most  nutritious  amongst 
the  proximate  principles  resulting  from  the  analysis  of  these 
vegetable  materials,  are  gluten,  farina,  mucilage,  oil,  and  sugar. 
The  seeds  of  cerealia  or  of  rice  constitute  the  chief  bulk  of  the 
food  in  those  countries  where  civilization  has  made  any  consider- 
able progress.  Of  all  these  kinds  of  grain,  wheat  appears  to 
contain,  in  proportion  to  its  bulk,  the  greatest  quantity  of  nutri- 
ment ;  and  this  arises  from  its  abounding  in  gluten,  which  of  all 
the  vegetable  principles  appears  to  be  best  adapted  to  the  human 
organs  of  digestion.  In  its  properties  it  bears  a  strong  resem- 
blance to  animal  substances ;  and  it  appears,  indeed,  by  chemical 
analysis,  to  contain  a  large  proportion  of  nitrogen.  Hence  it  may 
be  considered  as  the  most  animalized  of  the  vegetable  products. 
Gluten  is  contained  in  most  vegetables  which  afford  farina,  and 
is  also  found  in  the  leaves  of  many  esculent  vegetables,  such  as 
the  cabbage. 

315.  Farina  is  found  in  great  abundance  in  wheat  and  other 
grains,  and  also  forms  a  large  proportion  of  the  nutritive  por- 
tion of  rice,  and  of  certain  tubers,  among  which  the  principal  is 
the  potatoe.  The  leaves,  stalks,  and  seed-vessels  of  plants  are 
rendered  nutritious  by  the  mucilage  which  they  contain,  which  is 
generally  united  with  a  portion  of  sugar. 

316.  The  saccharine  principles  contained  in  vegetables,  and 
blended  with  other  elements,  contributes  greatly  to  render  them 
nutritious ;  though  in  its  pure  state,  as  extracted  from  the  sugar- 
cane, or  the  beet,  it  is  rather  used  as  a  grateful  addition  to  other  • 
articles  of  diet  than  as  a  separate  source  of  nutriment.  Sugar 
may  be  extracted  from  a  great  variety  of  plants  besides  those 
above  mentioned.  The  maple,  the  birch,  the  parsnip,  the  cocao- 
nut,  walnut,  maize,  and  carrot,  contain  it  in  great  abundance,  as 
is  the  case,  indeed,  with  every  species  of  grain  used  as  food. 
Almost  all  fruits  are  more  or  less  saccharine.  Figs,  grapes,  and 
dates,  which  contain  it  in  large  quantity,  form  a  very  consider- 
able proportion  of  the  food  of  the  inhabitants  of  the  south  of 
Europe,  and  the  African  nations  on  the  borders  of  the  Mediter- 
ranean. All  fruits  contain  a  basis  of  mucilage,  and  in  many  this 
mucilage  is  combined  with  oil  as  well  as  with  sugar.  , 

317.  Attempts  have  frequently  been  made  to  reduce  all  nutri- 
tious substances  to  a  single  principle  common  to  all  of  them,  and 
to  establish  accordinglv  a  scale  of  nutriment,  the  place  which 

13* 


150  NUTRITIVE    FUNCTIONS. 

any  substance  should  occupy  on  that  scale  being  regulated  by 
the  proportion  in  which  this  essential  principle  existed  in  it.  Hal- 
ler  conceived  that  jelly  might  be  considered  as  fulfilling  this  con- 
dition, and  as  being  the  essentially  nutritive  substance  in  nature.* 
Cullen  thought  that  this  property  appertains  to  two  substances, 
the  nutritous  matter  being  either  of  an  oily  or  saccharine  nature, 
or  consisting  of  these  two  qualities  combined.f  Richerand  con- 
siders alimentary  matter  as  either  gummy,  mucilaginous,  or  sac- 
charine.J  Dr.  Fordyce  referred  all  nutriment  to  the  presence  of 
mucilage.§  All  these,  and  many  other  attempts  at  generaliza- 
tion, made  by  different  physiologists  at  different  times,  are 
premature  and  unphilosophical,  since  they  associate  in  the  same 
class  substances  having  properties  totally  dissimilar,  although 
they  concur  only  in  that  of  affording  materials  for  the  support  of 
the  animal  system.  Perhaps  the  most  exact  classification  of  the 
kind  is  that  of  Magendie,  who  refers  all  alimentary  substances, 
whether  animal  or  vegetable,  to  the  following  heads,  namely, 
farinaceous,  mucilaginous,  saccharine,  acidulous,  oily,  caseous, 
gelatinous,  albuminous,  and  fibrinous. 

318.  Prout,  in  a  paper  published  in  the  Philosophical  Transac- 
tions,\\  thinks  that  all  the  articles  of  food  used  by  man  may, 
according  to  their  chemical  relations,  be  arranged  under  three 
heads,  namely,  tlie  saccharine,  the  albuminous,  and  the  oily.  Su- 
gar, the  basis  of  the  first  class  of  alimentary  substances,  he  finds 
to  consist  of  carbon  in  different  proportions,  from  thirty  to  fifty 
per  cent.  chemicaUy  combined  with  water.  The  basis  of  albu- 
men and  oil  are  more  compound,  but  are  also  united  with  water, 
the  proportion  of  carbon  existing  in  some  of  the  oils  being  nearly 
eighteen  per  cent.  He  is  of  opinion  that  two  at  least  of  these 
elements  must  be  blended  together  in  our  food  in  order  to  render 
it  either  nutritious  or  digestible.  Milk,  the  food  provided  by  na- 
ture for  the  young  animal,  exhibits  the  most  perfect  union  of  these 
three  elements. 

319.  It  must  be  evident,  however,  upon  a  shght  consideration, 
that  notwithstanding  all  the  attempts  that  have  been  made  to  es- 
tablish an  accurate  scale  of  nutriment,  more  must  depend- upon 
the  powers  possessed  by  the  digestive  organs  to  convert  the  par- 
ticular kind  of  food  into  nutritious  matter,  than  upon  its  being  able 
to  supply  the  elements  requisite  for  composing  nutriment.  Thus, 
there  are  many  substances,  such  as  oil  for  example,  which  con- 
tain a  very  large  proportion  of  the  elements  which  compose  the 
blood,  but  which  are  extremely  difficult  of  digestion,  and  conse- 
quently cannot  of  themselves  be  considered  as  nutritious,  although . 
when  blended  with  other  substances  which  contain  fewer  of  these 

*Elementa  Physiologioe,  xix.  3,  2.  f  Physiology,  §  211. 

"^Elemens  de  Physiologie,  §  3,  p.  82.        §  Treatise  on  Digestion,  p.  84. 
For  the  year  1827,  p.  355. 


PROPERTIES    OF    FOOD.  151 

elements,  but  which  enable  the  stomach  to  exert  a  .proper  action 
upon  the  compound,  they  become  highly  nutritive.  This  remark 
applies  also  to  sugar,  which,  although  adding  considerably  to 
the  nutritive  qualities  of  those  vegetable  products  which  contain 
it,  would  not,  if  used  alone,  be  capable  of  supporting  life.  Ma- 
gendie  found,  that  dogs  fed  upon  sugar  alone  soon  became 
unhealthy,  and  if  that  diet  was  persisted  in,  perished  from  inani- 
tion.* Dr.  Stark  made  numerous  experiments  upon  himself,  to 
which,  indeed,  he  ultimately  fell  a  victim ;  from  these  it  appears, 
that  substances  which  afford  most  nutriment,  if  their  use  be 
persevered  in  for  any  length  of  time,  to  the  exclusion  of  other 
diet,  soon  produce  derangement  of  the  stomach,  and  failure  of 
its  digestive  power.  Peculiarities  are  often  met  with  in  the 
stomachs  of  different  individuals  with  respect  to  the  power  of 
digesting  particular  kinds  of  food.  In  this  respect  much  depends 
upon  previous  habits  ;  so  that  it  is  scarcely  possible  to  establish 
any  general  rules  with  regard  to  the  nutritious  qualities  of  dif- 
ferent species  of  aliment,  that  are  not  invalidated  by  innumerable 
exceptions.  The  quantity  of  liquid  that  is  taken  in  along  with 
the  solid  food  is  also  exceedingly  various  in  different  individuals; 
that'which  is  suited  to  the  digestion  of  the  one  being  found  to 
disagree  with  another.  If  we  except  soups,  which  of  course 
consist  of  the  soluble  parts  of  materials  out  of  which  they  are 
prepared,  and  also  milk,  the  liquids  received  into  the  stomach 
rarely  contain  any  notable  proportion  of  nutritious  matter,  but 
seem  rather  to  aid  the  digestion  of  more  solid  food,  either  by 
supplying  the  place  of  a  solvent,  or  by  acting  as  a  stimulus  to 
the  stomach.  They  are  also  in  many  cases  necessary  for 
supplying  the  loss  occasioned  by  perspiration,  which  in  hot  cli- 
mates, by  regulating  the  temperature  of  the  body,  is  essen- 
tial to  the  peservation  of  health.  These  purposes  are  answered 
by  many  vegetable  infusions,  such  as  tea  and  coffee,  and  also  by 
fermented  liquors,  although  the  latter  contain  to  a  certain  extent 
many  of  the  materials  of  nutrition,  such  as  sugar  and  mucilage, 
besides  the  stimulant  principle  of  alcohol. 

3.  Condiments. 

320.  With  a  view  to  the  same  stimulant  effect,  various  sub- 
stances are  added  in  small  quantities  to  our  food,  which  act  as 
condiments.  Of  these  the  principal  is  common  salt,  a  taste  for 
which  seems  to  be  natural  to  a  great  number  of  animals,  and 
which,  used  in  small  quantity,  has  the  effect  of  promoting  diges- 
tion. Other  condiments,  such  as  pepper,  mustard,  garlic,  and 
various  other  spices  and  aromatics,  are  employed  chieffy  from 
the  agreeable  impression  they  make  upon  the  palate ;  but  they 

*  Physiologic,  torn.  ii.  p.  390. 


152  NUTRITIVE    FUNCTIONS. 

in  many  cases  check  the  tendency  of  fermentation  which  many 
kinds  of  food  are  Hable  to  undergo  in  the  stomach.  As  a  general 
rule,  to  which,  of  course,  there  are  many  exceptions,  whatever 
is  agreeable  to  the  palate  is  adapted  also  to  the  digestive  powers 
of  the  stomach.  A  certain  degree  of  variety  in  the  articles  of 
diet  is  more  conducive  to  the  nourishment  of  the  body  than 
confinement  to  any  single  article.* 


Sect.  IV. — Appetites. 
1.  Hunger. 

321.  Hunger  is  a  peculiar  sensation  excited  in  the  stomach  by 
the  want  of  food,  and  by  the  presence  of  the  gastric  juice  in  that 
organ  conjointly.  It  is  evidently  an  affection  of  the  nerves  of 
the  stomach,  for  it  is  a  good  deal  dependent  on  the  state  of  the 
nervous  system.  Its  periodical  recurrence  at  stated  times  §hows 
that  it  is  a  crood  deal  under  the  dominion  of  habit.  Huncrer  often 
suddenly  ceases  upon  the  occurrence  of  sudden  emotions  of 
grief  or  anger,  and  is  much  influenced  by  other  causes  of  mental 
excitation.  Literary  men  deeply  absorbed  in  meditation  often 
forget  that  they  have  occasion  for  nutriment,  and  are  unconscious 
of  the  calls  of  hunger.  Hence  such  persons  are  often  great 
sufferers  from  disordered  digestion. 

322.  The  presence  of  the  gastric  juice  appears  however  to  be 
a  natural  stimulus  to  appetite,  its  primary  action  being  probably 
in  the  nerves  of  the  stomach.  A  similar  efTect  may  be  produced, 
when  the  stomach  is  full,  by  taking  spirituous  liquors,  or  high- 
seasoned  dishes.  Those  physiologists  who  were  inclined  to  refer 
the  phenomena  of  the  living  body  to  mechanical  causes,  ascribed 
the  sensation  of  hunger  to  the  friction  of  the  surfaces  of  the  sto- 
mach against  one  another,  which  they  supposed  took  place  when 
it  was  empty ;  but  the  anatomy  of  that  organ,  which,  from  its 
rounded  form,  and  from  the  softness  of  its  texture,  would  seem 
totally  incapable  of  producing  friction  by  any  of  its  movements, 
is  totally  at  variance  with  this  hypothesis.  Others  have  conceived 
that  the  collapse  of  the  stomach  in  its  empty  state,  by  deranging 

*  [So  much  is  this  the  case,  that  if,  after  an  individual  has  been  accustomed 
to  live  on  both  animal  and  ve^-etable  food,  he  be  restricted  to  one  only,  his 
nutrition,  in  course  of  time,  becomes  impaired,  and  scurvy  is  induced.  There 
is  at  this  time,  (June,  1839,)  in  the  wards  of  the  Philadelphia  Hospital, 
Blockley,  a  female,  who  has  refused  all  animal  food  for  many  months,  and 
who  is  effectpd  with  purpura  on  the  extremities,  spontry  gums,  and  every  sign 
of  anaemia.  It  is  this  restriction  to  a  single  article  of  diet,  with  the  confine- 
ment to  a  small  space,  and  the  privation  of  wonted  air  and  exercise,  that 
explains  the  phenomena  observed  in  the  dog  fed  exclusively  on  sugar,  (§  319) 
better  than  the  want  of  azote  in  the  aliment  to  which  it  was  at  one  time 
ascribed  by  Magendie.] 


APPETITES.  153 

the  position  of  tiie  liver  and  spleen,  drags  down  the  diaphragm, 
and  thus  excites  irritation  in  the  nerves  of  those  regions  ;  and 
they  endeavour  to  support  this  doctrine  by  the  alleged  fact,  that 
hunger  is  prevented  and  appeased  by  wearing  a  tight  girdle, 
which  occasions  pressure  on  the  stomach  and  gives  support  to 
the  neighbouring  organs.  But  the  instances  already  given  of  the 
dependence  of  hunger  on  the  states  of  the  nervous  system,  are 
sufficient  to  prove  that  it  is  not  owing  to  any  mechanical  cause. 

323.  The  chemical  physiologists  attempted  to  explain  the  phe- 
nomena solely  by  the  action  of  the  gastric  juice  on  the  coats  of 
the  stomach,  which  they  imagined  it  tended  to  corrode,  and 
hence  gave  rise  to  an  uneasy  sensation.  It  is  much  more  pro- 
bable, however,  that  the  impression  made  by  -this  secretion  is 
exclusively  on  the  nerves  of  the  stomach;  and  there  is  no  doubt 
but  that  this  action  is  one  of  the  principal  causes  of  hunger;  for  it 
has  been  found,  that,  if  after  long  fasting,  when  there  is  a  con- 
siderable accumulation  of  gastric  juice,  and  when  the  sensation 
of  hunger  is  extremely  intense,  it  at  once  ceases  if  the  gastric 
juice  be  removed  by  an  emetic;  or  even  if  it  be  much  diluted  by 
taking  large  quantities  of  hot  water.* 

324.  The  effects  of  long  abstinence  from  food  are,  great  loss 
of  strength,  emaciation,  discoloration  of  the  blood  and  of  the 
secretions,  an  increase  of  nervous  susceptibility,  fever,  loss  of 
sleep,  painful  sensations  in  the  region  of  the  stomach,  followed 
by  total  loss  of  appetite,  delirium,  and  death.  It  has  been  said, 
that  the  exterior  of  the  bodies  of  those  who  die  of  famine  has 
exhibited  a  shining  appearance  in  the  dark,  as  if  they  had  been 
impregnated  with  uncombined  phosphorus. 

2.  Thirst. 

325.  Thirst  is  a  sensation  somewhat  analo!2;ous  tohunsrer  with 
respect  to  its  cause  and  effect,  and  with  respect  of  its  depending 
on  particular  states  of  the  nervous  system.  It  is  considerably 
more  distressing  and  intolerable  than  hunger.  The  seat  of  the 
sensation  appears  to  be  in  the  mouth  and  fauces,  although  its 
origin  is  generally  in  the  state  of  the  stomach,  or  general  condi- 
tion of  the  system.     In  the  healthy  condition  of  the  organs  it  is 

*  [These  reasons  are  not  satisfactory.  The  circunnstariees  referred  to,  tend 
merely  to  show,  what  we  observe  constantly  as  the  effect  of  mental  emotions — 
that  the  sensation  of  hunger  can  be  postponed  for  a  time.  An  unanswerable 
objection  to  them,  l^wever,  is  the  fact,  repeatedly  proved  by  Dr.  Beaumont,  and 
verified,  in  the  same  case,  by  Dr.  Dunglison,  that  in  the  fasting  state  there  is 
little  if  any  gastric  juice  in  the  stomach.  Hunger  is  an  internal  sensation 
connected  with  the  wants  of  the  economy;  instinctive,  therefore,  and  as  inex- 
plicable— in  the  existing  state  of  knowledge — as  any  other  internal  sensation. 
— Beaumonfs  Experiments  and  Observations  on  the  Gastric  Juice,  &c.  p.  57, 
Plattsburg,  1833,  and  Dunglison''s  Human  Physiulugy,  3d  edit.  i.  493.] 


154  NUTRITIVE    FUNCTIONS. 

a  natural  impulse  prompting  us  to  supply  the  system  with  the 
fluids  requisite  for  carrying  on  its  functions ;  but  in  the  case  of 
fevers,  and  other  morbid  states,  thirst  is  sometimes  excessive, 
and,  if  indulged  without  restriction,  would  prove  highly  injurious. 
In  cases  where  a  preternatural  opening  has  been  made  into  the 
oesophagus  through  the  neck,  the  sensation  of  thirst  is  found  not 
to  be  in  any  degree  assuaged  by  fluids  appHed  to  the  mouth,  or 
even  swallowed,  if  they  escape  through  the  wound,  and  do  not 
descend  into  the  stomach ;  whereas,  it  is  immediately  relieved 
when  the  same  fluids  are  introduced  into  the  stomach. 


Sect.  V. — Pre'paration  of  the  Food  for  Digestion. 

320.  The  preparatory  processes  to  which  the  food  is  subjected 
previous  to  its  introduction  into  the  stomach,  are  partly  of  a 
mechanical  and  partly  of  a  chemical  nature.  It  is  .masticated 
by  the  teeth  and  jaws,  and  at  the  same  time  mixed  with  the  saliva 
and  mu&ous  secretions  of  the  membrane  hning  the  mouth,  fauces, 
and  oesophagus.  The  effect  produced  by  these  operations  is  to 
reduce  the  food  to  a  soft  and  uniform  pulp,  which  is  more  easil}'- 
acted  upon  by  the  solvent  powers  of  the  gastric  juice  than  if  it 
had  been  swallowed  entire. 


1.  Mastication. 

327.  During  mastication,  a  great  number  of  muscles  are  called 
into  action.  The  principal  of  these  are  the  powerful  muscles  that 
elevate  the  lower  jaw, — namely,  the  temporal,  the  masseter,  and 
the  pterygoid,  the  latter  of  which  .are  capable  of  giving  at  the 
same  time  some  degree  of  lateral  motion  to  the  jaw,  adapting  it 
thereby  to  effect  a  grinding  action  by  the  medium  of  the  teeth. 
The  lower  jaw  forms  a  lever  of  the  third  kind  with  a  double 
angle,  the  fulcrum  being  at  the  condyles,  which  are  curiously 
articulated  with  the  skull,  by  means  of  an  interposed  cartilage. 
Its  motions  are  almost  entirely  confined  to  those  of  elevation 
and  depression ;  but  it  has  also  a  more  limited  extent  of  lateral 
motion. 

328.  The  teeth,  are  the  great  agents  in  mastication.  The 
respective  purposes  served  by  each  class  are  sufficiently  evident 
from  their  shape  and  position  in  the  jaw.  The  incisors  or  front 
teeth,  are  employed  for  cutting  or  dividing  the  food  like  a  pair 
of  shears  or  scissors ;  the  cuspidati,  or  eye-teeth,  placed  a  little 
farther  back  in  the  jaw,  are  particularly  adapted  to  lay  hold  of, 
and  tear  asunder,  fibrous  textures  that  afford  considerable  re- 
sistance; their  action  may  be  compared  to  that  of  pincers.  Mr. 
Hunter,  after  reviewing  their  different  forms  in  the  different  tribes 


PREPARATION    OF    THE    POOD    FOR    DIGESTION.  155 

of  qua'drupeds,  is  enabled  to  trace  a  similarity  in  shape,  situation, 
and  use  of  tiie  cuspidati,  from  the  most  imperfect  carnivorous 
animal,  which  he  believes  to  be  the  human  species,  to  the  most 
perfect  carnivorous  animal,  the  lion.  The  bicuspidati  and  molares 
compose  what  are  called  the  grinding  teeth,  and  their  chief  office 
is  the  trituration  of  substances  already  torn  ofi"  by  the  cuspidati, 
or  cut  by  the  meeting  of  the  incisors.  The  molares  especially, 
being  placed  nearer  to  the  articulation  of  the  jaw,  or  centre  of 
motion,  act  with  greater  power  in  exerting  pressure  on  whatever 
is  between  them.  If  we  wish  to  break  a  very  hard  body,  the 
shell  of  a  nut  for  example,  we  instinctively  place  it  between  the 
•backmost  molares,  where  the  resistance  it  opposes  to  fracture 
acts  by  the  shortest  lever. 

The  bony  substance  of  the  teeth  is  preserved  from  the  injury 
to  which  it  would  be  exposed  by  the  friction  of  hard  substances, 
and  by  the  contact,  of  corroding  fluids,  and  the  influence  of  the 
air,  by  being  cased  in  enamel,  which,  as  we  have  seen,  is  con- 
siderably harder  than  bone.  In  consequence  of  the  peculiar  mode 
of  its  formation,  the  enamel  is  incapable  of  being  renewed  by  a 
fresh  growth  when  it  has  been  worn  away  by  friction.  When, 
however,  the  teeth  are  lost  by  age,  accident,  or  disease,  their 
alveoli  close  and  are  obliterated  by  absorption ; 'the  gums  then 
acquire  a  degree  of  hardness,  that  renders  them  an  imperfect 
substitute  for  the  teeth  in  mastication. 

329.  The  chief  agent  in  distributing  the  food  so  as  to  place 
it  in  proper  situations  between  the  teeth  for  the  purpose  of  mas- 
tication, and  for  transferring  it  to  the  fauces,  is  the  tongue.  This 
organ  consists  almost  entirely  of  muscular  fibres,  which  are 
variously  arranged,  and  interwoven  together  in  a  very  intricate 
manner,  so  as  to  render  it  capable  of  motion  in  every  possible 
direction.  Its  root  is  affixed  to  a  bone  which  is  peculiar 'to  it, 
called  the  os  hyoides,  from  its  resemblance  to  the  Greek  letter  ", 
which  furnishes  a  basis  of  attachment  to  the  greater  number  of 
the  muscles  of  the  tongue,  and  the  extremities  of  which,  being 
extended  considerably  backwards,  serve  to  keep  the  palate  ex- 
panded and  always  prepared  to  receive  the  food.  But  the  tongue 
also  contains  a  set  of  muscular  fibres,  which  proceed  longitudi- 
nally through  the  centre  of  that  organ,  unattached  to  any  bone, 
and  serving  to  contract  its  length.  The  tongue,  is  thrust  out  of 
the  mouth,  not  by  any  power  of  elongation  in  the  muscles,  as 
might  at  first  sight  appear  to  be  the  case,  but  by  the  contraction 
of  that  portion  of  the  radiating  fibres  proceeding  backwards  from 
the  inside  of  the  jaw  and  the  os  hyoides',  and  drawing  forwards 
the  root  of  the  tongue  when  they  act  alone.  This  complex  struc- 
ture is  admirably  adapted  to  the  great  variety  of  uses  to  which 
the  tongue  is  applied,  not  only  in  mastication  and  deglutition, 
but  also  in  speaking. 


156  NUTRITIVE    FUNCTIONS. 

330.  The  muscular  actions  of  the  lips  and  cheeks  are  also 
mintimately^concernedin  mastication  ;  and  ample  provisionis  made 
for  their  varied  movements  by  being  furnished  with  so  great  a 
number  of  muscles  as  those  which  cover  the  face,  and  are  attached 
more  or  less  to  the  lips  and  corners  of  the  mouth. 

2.  Insalivat'wn. 

331.  While  the  food  is  under  the  action  of  the  organs  of  mas- 
tication which  effect  its  mechanical  division,  it  is  at  the  same 
time  mixed  up  with  the  saliva.  This  fluid  is  found,  when  chem- 
ically examined,  to  consist  principally  of  mucus  and  albuminous 
matter  held  in  solution  in  water,  together  with  a  small  proportion 
of  saline  ingredients. 

332.  Dr.  Bostock  considered  that  he  had  detected  two  kinds 
of  animal  matter  in  the  saliva,  one  composing  the  soft  masses, 
and  giving  it  its  consistence  and  physical  characters,  nearly 
similar  to  coagulated  albumen,  the  other  dissolved  in  the  water 
of  the  fluid  along  with  the  salts,  and  resembling  the  serosity  of 
the  blood.*  Berzelius  regards  the  former  of  these  substances  as 
corresponding  in  its  properties  to  mucus,  and  states  the  saline 
ingredients  to  be  chiefly  alkaline  muriates,  with  a  small  quantity 
of  lactate  of  soda  and  of  pure  soda.f  Tiedemann  and  Gmehn 
state  the  solid  contents  of  the  saliva  to  vary  from  one  to  twenty- 
five  per  cent,  and  to  consist  of  salts,  mucus,  and  ozmazome,  to 
which  are  added,  in  some  cases,  a  little  albumen  and  a  little 
fatty  matter,  containing  phosphorus.  The  soluble-salts  consist 
of  alkaline  carbonate,  w^hich  gives  an  alkaline  character  to  the 
fluid,  acetate,  phosphate,  sulphate,  muriate,  and  sulpho-cyanate. 
The  alkali  in  man  is  almost  solely  potass  ;  while,  in  the  dog  and 
sheep,  it  consists  of  soda,  with  very  little  potass.  The  presence 
of  sulpho-cyanic  acid,  on  the  other  hand,  is  almost  peculiar  to 
the  human  saliva,  being  scarcely  perceptible  in  that  of  the  dog. 
Some  insoluble  salts,  namely,  phosphate  of  lime,  carbonate  of 
lime,  and  carbonate  of  magnesia,  are  also  detected  in  the  saliva, 
but  in  very  minute  quantity.  J  Leuret  and  Lassaigne,  whose  inves- 
tigations were  nearly  contemporaneous  with  those  of  Tiedemann 
and  Gmelin,  represent  the  chemical  properties  of  the  saliva  as  be- 
ing essentially  the  same  in  all  animals,  and  consider  the  animal 
matter  it  contains  as  a  species  of  mucus.§ 

333.  When  viewed  by  a  good  microscope,  the  saliva  is  gene- 
rally found  to  contain  globules  of  very  minute  size. 

*  Edin.  Med.  Journal,  ii.  44. 
f  Medico-Chirurgical  Transactions,  iii.  242. 
X  Recherches  sur  la  Digestion,  par  Jourdan,  p.  23. 

§  Recherches  Physiologiqnes  et  Chinniques  sur  la  Digestion,  p.  33.  See 
Bostock's  Elementary  System  of  Physiology,  p.  487,  note. 


PREPARATION    OF    THE    POOD    FOR    DIGESTION.  157 

334.  The  saliva  is  secreted  by  the  parotid  and  other  glands  in 
the  vicinity  of  the  mouth>  and  is  poured  out  in  considerable  quan- 
tities during  mastication.  It  lias  been  estimated  that  about  six  or 
eight  ounces  of  saliva  are  at  each  principal  daily  meal  mixed  up 
and  incorporated  with  the  food.  It  flows  much  more  abundantly 
during  a  meal,  and  particularly  if  the  food  that  is  eaten  possesses 
stimulating  qualities,  and  has  a  sapid  flavour.  The  quantity  is 
augmented  by  the  appearance,  or  even  the  idea  of  food,  when 
the  appetite  is  keen.  The  influence  of  the  nerves  which  supply 
the  salivary  glands  is  very  marked  in  regulating  their  secretions, 
as  we  shall  have  occasion  to  observe  more  at  length,  when  we 
come  to  consider  the  function  of  secretion.  The  pressure  of  the 
muscles  of  the  cheek  on  the  parotid  gland  assists  no  doubt  in  the 
quick  discharge  of  the  secretion  of  that  gland  by  its  excretory 
ducts;  and  the  same  remark  applies  also  to  the  submaxillary  and 
sublingual  glands,  which  also  prepare  saliva,  and  whose  ducts 
open  into  the  mouth :  for  we  find,  that  during  mastication  all  the 
muscles  about  the  mouth  are  in  continual  action.  The  tongue 
presses  the  food  on  all  sides,  and  thrusts  it  between  the  grinding 
teeth,  while  the  muscles  of  the  cheek,  but  more  particularly  the 
buccinator,  against  which  the  food  is  pressed  by  the  tongue, 
forces  it  back  again  under  the  teeth,  until  it  has  been  sufficiently 
subjected  to  their  action ;  and  during  the  whole  of  this  time  it 
is  gradually  receiving  additions  of  saliva,  which  thus  become 
intimately  and  uniformly  mixed  up  with  every  portion  of  the 
divided  food.  When  completely  chewed,  it  is  collected  together 
on  the  surface  of  the  tongue,  which  sweeps  round  the  different 
parts  of  the  mouth  for  this  purpose,  and  moulds  it  into  the  form  of 
a  bolus  ;  and  the  point  of  the  tongue  being  then  raised,  and  its 
basis  depressed,  an  inclined  plane  is  formed,  along  which  the 
bolus  is  propelled  backwards,  and  delivered  to  the  pharynx, 
which  is  expanded  to  receive  it. 

3.  Deglutition. 

335.  The  action  of  swallowing,  simple  as  it  may  appear  to  be, 
is  in  reality  extremely  complex,  consisting  of  a  succession  of 
muscular  contractions,  nicely  adjusted  and  balanced,  so  as  to 
co-operate  harmoniously  in  the  production  of  one  general  effect, 
the  descent  of  the  food  along  the  cesophagus.  The  whole  exhibits 
one  of  the  most  beautiful  examples  of  mechanical  contrivance 
that  is  to  be  met  with  in  the  body. 

336.  The  pharynx,  as  we  have  seen,  is  a  large  muscular  bag, 
shaped  hke  a  funnel,  capable  of  being  contracted  in  diameter, 
and  of  compressing  its  soft  contents  by  means  of  the  muscles 
which  are  expanded  round  it,  and  are  called  the  constrictors  of 
the  pharynx.     Other  muscles  are  provided  for  elevating  it,  that 

,     14 


158  NUTRITIVE    FUNCTIONS. 

is,  for  bringing  it  nearer  to  the  base  of  the  tongue.  While  the 
food  is  passing  downwards,  the  velum  pendulum  is  expanded, 
thrown  backwards,  and  raised  by  the  muscles  adapted  to  perform 
these  motions,  so  that  it  closes  the  posterior  nostrils,  and  acting 
as  a  valve,  prevents  any  portion  of  what  is  swallowed  from  pass- 
ing either  into  those  cavities  or  into  the  eustachian  tubes.  The 
bolus  is  thus  directed  towards  the  oesophagus,  being  carried 
thither  by  the  contraction  of  the  pharynx,  while  the  root  of  the 
tongue  being  at  the  same  time  depressed,  the  epiglottis  is  turned 
backwards,  and  being  applied  to  the  glottis,  accurately  closes  its 
■aperture,  so  that  no  part  of  the  alimentary  matter  can  pass  into 
the  larynx.  The  mass  of  food,  having  now  arrived  at  the  upper 
part  of  the  oesophagus,  is  propelled  towards  the  stomach  by  the 
successive  contractions  of  its  circular  fibres.  The  mucus,  which 
is  secreted  in  abundance  by  all  the  surfaces  along  which  it  passes, 
and  continually  lubricates  them,  very  much  facilitates  its  descent. 
The  longitudinal  fibres  of  the  muscular  coat  of  the  cesophagus 
contribute  their  share  in  this  action,  by  shortening  and  dilating 
those  portions  of  the  canal  into  which  the  food  is  about  to  enter, 
Dumas  distinguishes  four  stages  in  this  process ;  first,  that  by 
which  the  aliment  is  propelled  towards  the  pharynx ;  the  second, 
consisting  in  the  dilation  of  that  cavity,  by  which  it  receives  the 
bolus  transmitted  to  it ;  the  third,  by  which  the  pharynx  closes 
upon  its  contents,  and  propels  it  downwards  to  the  oesophagus ; 
and  the  fourth,  in  which,  by  the  action  of  the  cesophagus,  the 
food  is  propelled  into  the  stomach.* 

337.  When  any  impediment  exists  to  the  due  performance  of 
these  actions,  fluids  are  swallowed  with  greater  difficulty  than 
solids,  because  the  particles  of  the  former  having  a  continual 
tendency  to  spread  themselves,  it  requires  a  closer  and  more 
exact  application  of  the  organs  to  prevent  their  escape,  while 
they  are  compressed  in  giving  to  the  fluid  its  proper  direction. 
The  action  of  suction  performed  by  the  tongue,  with  the  assist- 
ance of  the  muscles  of  the  cheeks  and  lips,  which  remove  the 
pressure  of  the  atmosphere  from  the  surface  of  the  fluid  to  which 
the  mouth  is  applied,  is  also  very  complex.  The  tongue  acts  here 
as  a  piston ;  and  sometimes  the  action  is  effected  by  the  muscles 
of  inspiration. 


Sect.  VI. — Digestion  or  Chymification. 

338.  The  food  has  now  passed  from  the  oesophagus  into  the 
stomach,  through  its  cardiac  orifice,  which  has  so  been  named 
from  its  supposed  sympathy  with  the  heart,  near  which  it  is 

'  Physiologie,  torn.  i.  p.  341. 


DIGESTION    OR    CHYMIFICATION.  159 

situate.  The  office  of  the  stomach  is  to  convert  the  food  which 
it  receives  into  the  soft  pultaceous  mass  of  a  gray  colour,  wliich 
has  been  denominated  chyme.*  These  secretions  do  not  proceed 
from  any  glands  that  admit  of  being  readily  distinguished,  their 
existence  being  rather  inferred  from  the  presence  of  the  secre- 
tion. The  membranes  composing  the  coats  of  the  stomach  are 
capable  of  great  distension,  so  as  to  contain  a  large  quantity  of 
food,  while  at  other  times  that  organ  is  contracted  to  a  very 
small  size,  partly  by  the  elasticity  of  its  texture,  but  principally 
by  the  action  of  the  circular  and  longitudinal  fibres  which  encom- 
pass its  cavity,  and  which  constitute  its  muscular  coat.  These 
fibres  are  so  disposed  as  to  enable  different  portions  of  the  sto- 
mach to  act  separately  and  successively  on  its  contents,  producing 
what  has  been  termed  the  -peristaltic,  or  vermicular  motion.  Two 
purposes  are  answered  by  these  actions;  in  the  first  place,  the  food 
contained  in  the  stomach  is  asiitated  and  thorouarhlv  mixed  to- 
gether,  while  it  is  at  the  same  time  exposed  to  the  chemical  action 
of  the  gastric  juice ;  and  secondly,  the  ultimate  effect  of  this 
motion  is  to  carry  the  mass  very  gradually  towards  the  pylorus, 
through  which  it  is  transmitted  into  the  beginning  of  the  intesti- 
nal canal. 

339.  While  the  food  is  thus  rolled  and  agitated  by  the  peris- 
taltic action  of  the  muscles,  it  is  at  the  same  time  subjected  to  a 
degree  of  pressure,  the  purpose  of  which  seems  to  be,  to  bring 
into  closer  approximation  the  solvent  f]uids  with  the  materials  on 
which  they  are  to  act,  and  thereby  increase  the  chemical  power 
of  the  former,  and  also  to  repress  the  evolution  of  gas,  which  has 
a  tendency  to  be  generated  during  the  species  of  fermentation 
which  the  aliment  undergoes  in  the  process  of  digestion. 

340.  The  principal  agents  in  effecting  those  changes  which 
constitute  digestion,  that  is,  which  convert  the  aliment  into 
chyme,  is  the  gastric  juice.  The  important  office  which  this 
secretion  performs  has  induced  chemists  to  bestow  great  pains 
in  obtaining  its  correct  analysis,  and  in  examining  all  its  physical 
properties.  When  carefully  collected,  it  appears  to  be  a  trans- 
parent and  colourless  fluid,  having  a  saline  and  somewhat  bitter 
taste,  occasionally  possessing  acid  properties,  but  probably  in  its 
natural  and  healthy  condition  being  neither  acid  nor  alkaline.f 
It  contains  a  small  proportion  of  albumen,  together  with  a  matter 
which  is  either  gelatin  or  mucus.  But  while  it  thus  differs  to  all 
appearance  in  so  trifling  a  degree  from  many  of  the  other  sccre- 


*  The  older  authors  made  no  distinction  between  chyme  and  chyle:  the  lat- 
ter substance  is  the  product  of  the  formation  of  the  small  intestines. 

f  [This  is  more  than  questionable.  Whenever  the  secretions  of  the  stomach 
have  been  obtained  unmixed  w^ith  alimentary  matters,  as  in  the  case,  referred 
to  hereafter,  of  the  man  with  the  fistulous  aperture  into  the  organ,  they  were 
found  of  a  distinctly  acid  taste.] 


160  NUTRITIVE    FUNCTIONS. 

tions,  it  yet  possesses  very  extraordinary  solvent  powers  over  the 
substances  usually  employed  as  food.  Even  when  made  to  act 
upon  these  substances  in  vessels  out  of  the  body,  provided  they 
are  kept  in  a  temperature  equal  to  that  of  the  human  body,  it 
will  reduce  them  in  a  few  hours  to  the  state  of  a  soft  pulp,  pro- 
ducing apparently  the  very  same  change  which  is  induced  upon 
the  same  species  of  aliment  by  the  digestive  process  within  the 
stomach.  It  is  evident  that  the  chemical  analysis  of  the  gastric 
juice  affords  as  yet  no  clue  to  the  explanation  of  this  singular 
property.  The  power  which  the  gastric  juice  possesses  of 
coagulating  milk,  and  other  albuminous  fluids,  and  of  retarding 
the  putrefaction  of  animal  and  vegetable  substances  subjected  to 
its  action,  and  even  of  counteracting  this  process  when  it  has 
already  commenced,  are  equally  involved  in  mystery,  and  baffle 
all  our  endeavours  to  explain  them  on  any  of  the  hitherto  known 
chemical  principles.* 

341.  There  are  three  ways  in  which  the  gastric  juice  has  been 
observed  to  act  on  alimentary  matter ;  the  -firsi  is  that  of  coagu- 
lation, which  is  exerted  on  all  the  fluid  forms  of  albumen,  whether 
existing  in  the  serum  of  the  blood,  or  the  white  of  the  egg,  or  in. 
different  secretions,  more  especially  milk.  It  is  by  means  of  this 
property,  indeed,  that  cheese  is  obtained  from  the  coagulation  of 
its  albuminous  portion  by  the  addition  of  rennet,  which  is  an 
infusion  of  the  digestive  stomach  of  a  calf.  The  object  of  this 
coagulation  appears  to  be  to  detain  the  substance  for  a  longer 
time  in  the  stomach,  and  subject  it  more  completely  to  the  solvent 
power  of  the  same  fluid,  by  previously  acquiring  a  solid  form, 
which  prevents  its  escape  by  the  pylorus. 

342.  The  second  kind  of  action  exerted  on  the  food  by  the 
gastric  juice  is  that  of  counteracting  the  tendency  to  putrefaction, 
and  even  to  the  ascescent  fermentation.  This  efl^ect  takes  place 
in  a  remarkable  degree  in  many  carnivorous  animals,  who  fre- 
quently take  their  food  in  a  half  putrid  state ;  and  in  whom  the 
first  operation  of  the  gastric  juice  is  to  remove  from  it  all  putres- 
cence; showing  that  this  secretion  possesses  the  property  not  only 
of  preventing  putrefaction  from  taking  place,  but  also  of  suspend- 
ing its  further  progress  when  it  has  actually  commenced. 

343.  The  third  species  of  chemical  action  exhibited  by  the 
gastric  juice  is  that  of  solution.  That  this  effect  takes  place  inde- 
pendently of  any  concurrent  mechanical  operation  of  the  muscular 
powers  of  the  stomach  has  been  very  decisively  proved  by  the 

*[  Some  interesting  experiments  have  been  made  on  the  powers  of  acidified 
mucus  in  effecting  artificial  digestion,  by  Eberle  of  Germany,  Professor 
Miiller  and  D.  Schwann,  and  by  Dr.  T  J.  Tood.  By  steeping  the  mucous 
membrane  of  an  animal's  stomach  in  an  acid  liquor  a  solution  is  obtained,  to 
which  Eberle  gave  the  name  Pepsine.  This  solution  has  the  property  of 
dissolving  coagulated  albumen,  muscular  fibre,  and  animal  matters  in  general.] 


DIGESTION    OR    CHYMIFICATION.  161 

experiments  of  Reaumur,  of  Stevens,  and  of  Spallanzani.  Those 
of  Stevens,  in  particular,  are  highly  valuable,  from  being  made 
on  the  human  subject.  He  was  fortunate  enough  to  meet  with  a 
man  who  had  been  in  the  habit  of  swallowing  stones,  which  he 
could  afterwards,  by  a  voluntary  effort,  reject  by  vomiting  from 
his  stomach.  Taking  advantage  of  this  power,  Stevens  induced 
him  to  swallow  hollow  metallic  spheres  perforated  with  holes, 
and  filled  with  diflerent  kinds  of  alimentary  substances,  which, 
after  being  allowed  to  remain  a  sufficient  time  in  the  stomach, 
were  returned,  and  their  contents  examined.  It  was  invariably 
found  that  the  food  under  these  circumstances  of  exposure  to  the 
gastric  i^uid  alone,  and  protection  from  external  pressure  of  a 
mechanical  nature,  was  more  or  less  completely  dissolved,  and 
reduced  to  the  state  of  a  pulp.  He  afterwards  pursued  a  similar 
train  of  experiments  on  dogs,  causing  them  to  swallow  the  per- 
forated spheres,  and  after  a  certain  time  destroying  the  animals, 
and  examining  the  changes  effected  in  their  contents. 

344.  Spallanzani  has  also  varied  and  multiplied  experiments  of 
this  kind  in  a  manner  that  leaves  no  room  to  doubt  the  truth  of 
the  conclusion  deduced  from  them  as  to  the  solvent  power  of  the 
gastric  secretion.  Dense  membranes  and  even  bones  are  reduced 
into  a  pulpy  mass  by  this  fluid  in  many  animals,  while  at  the 
same  time  many  bodies  of  comparatively  delicate  textures,  such 
as  the  skin  of  fruits,  and  the  fibres  of  flax  or  cotton,  are  not  in 
the  slightest  degree  affected  by  it.  This  difference  of  action  on 
different  subjects  is  analogous  to  the  operation  of  chemical  affinity, 
and  corroborates  the  theory  that  digestion  is  effected  principally  by 
chemjcal  agency.  The  results  of  these  experiments  have  been 
fully  confirmed  by  experiments  made  on  the  stomachs  of  persons, 
who,  in  consequence  of  a  wound,  had  a  permanent  opening  into 
that  organ  through  the  parietes  of  the  abdomen. 

345.  Portions  of  the  stomach  are  sometimes  found  dissolved 
after  death.  This  takes  place  more  especially  when  death  has 
occurred  suddenly  during  the  act  of  digestion.  This  effect  can 
never  take  place  during  life,  because  the  living  structures  resist 
the  solvent  power  of  the  gastric  juice,  which  affects  only  dead 
animal  matter.  Thus  it  happens  that  worms,  and  the  larvas  of 
insects  live  for  a  considerable  time  in  the  stomach,  without  being 
acted  upon  by  its  secretions. 

346.  Gas  is  frequently  evolved  in  the  stomach  during  the  pro- 
cess of  digestion ;  but  this  W'ould  appear  to  take  place  onl}'  in  a 
disturbed  or  morbid  condition  of  that  process,  and  by  no  means 
to  be  a  necessary  attendant  upon  healthy  digestion. 

347.  Acid  is  also  frequently  developed  during  imperfect  diges- 
tion ;  but  it  appears  from  the  experiments  of  Dr.  Prout,  which 
have  been  fully  confifmed  by  other  experimentalists,  that  this 
effect  is  also  attendant  upon  healthy  digestion,  and  that  it  is  prin- 

14* 


162  NUTRITIVE    FUNCTIONS. 

cipally  the  muriatic  acid  whicii  is  thus  disengaged  from  its  com- 
binations, and  makes  its  appearance  in  a  free  state.  The  lactic 
acid,  an  acid  which  appears  to  be  a  modification  of  the  acetic, 
also  is  present  in  considerable  quantity. 

Professor  Tiedemann  and  Gmelin,  in  an  elaborate  treatise  on 
Digestion  lately  published,  found  the  acetic  acid  always  present 
in  the  gastric  juice.*  They  observe  that  water  alone,  at  the 
temperature  of  the  human  body,  is  capable  of  dissolving  many 
of  the  substances  employed  as  food  ;  and  of  these  many  that  are 
not  soluble  in  water  are  so  in  the  diluted  muriatic  and  ^acetic 
acids  at  a  high  temperature,  and  they  are  inclined  to  ascribe  to 
a  chemical  solution  of  this  kind  the  principal  change  effected  by 
digestion. 

348.  Among  the  agents  concerned  in  the  digestion  of  the  ali- 
ment, the  high  temperature  at  which  the  contents  of  the  stomach 
and  intestines  is  retained,  must  be  considered  as  one  of  the  most 
important.  The  heat  of  the  body  unquestionably  tends  to  pro- 
mote the  chemical  action  of  the  secretions  which  effect  these 
changes.  Whilst  digestion  is  taking  place,  both  orifices  of  the 
stomach  are  closed,  and  there  often  comes  on  a  feeling  of  chilli- 
ness, especially  in  a  weakly  constitution,  in  consequence  of  the 
demand  which  the  stomach  makes  upon  it  for  an  additional  sup- 
ply of  heat  to  assist  in  the  process  that  is  going  on.  There  is 
also  a  disinclination  to  exertion,  and  frequently  a  tendency  to 
sleep  while  digestion  is  performing.  Yet  the  indulgence  in  this 
disposition,  as  well  as  violent  exercise  immediately  after  a  meal, 
lend  equally  to  retard  the  formation  of  chyme.  The  circum- 
stances most  favorable  to  perfect  digestion,  are  gentle  exercise, 
with  cheerfulness,  and  moderate  mental  exertion. 

349.  It  appears  from  Dr.  W.  Philip's  experiments,  which  were 
conducted  chiefly  on  rabbits,  that  food  recently  taken  is  always 
kept  distinct  and  unmixed  with  that  which  has  remained  for  some 
time  in  the  stomach,  the  former  being  introduced  into  the  centre 
of  the  mass  previously  present.  The  food  is  more  digested  the 
nearer  it  is  to  the  surface  of  the  stomach,  and  is  least  digested  in 
the  small  curvature,  more  so  at  the  larger  end,  and  still  more 
perfectly  at  the  middle  of  the  great  curvature.  The  state  of  the 
food  found  in  the  cardiac  portion  is  different  from  that  found  in 

=•  [In  the  case  referred  lo  in  a  subsequent  paragraph  (349)  Dr.  Beaumont 
had  innumerable  opportunities  for  obtaining  the  gastric  secretions  unmixed 
with  alimentary  matter.  These  were  examined  by  Drs.  Dunglison  and  Em- 
met, and  found  lo  contain  free  muriatic  and  acetic  acids,  phosphates  and  mu- 
riates, with  bases  of  potassa,  soda,  magnesia,  and  lime,  and  an  animal  matter 
soluble  in  cold  water,  but  insoluble  in  hot.  The  quantity  of  free  muriatic  acid, 
contained  in  them  was  surprising.  On  repeated  examination,  the  acid  charac- 
ter was  distinct,  and  the  odour  of  muriatic  acid  not  lobe  doubted. — See  a  letter 
from  Dr.  Dunglison  to  Dr.  Beaumont,  in  Beaumont's  Experiments,  &c.,  on 
the  Gastric  Juice,  p.  78.] 


DIGESTION    OR    CHYMIFICATION.  163 

the  pyloric  portion  of  thO  stomach ;  for  in  the  latter  it  is  nnore 
uniform  in  its  consistence,  more  dry  and  compact,  and  apparent- 
ly more  thoroughly  digested.  Thus  it  would  appear  that  it  is  at 
the  large  end  of  the  stomach  where  the  gastric  juice  is  secreted 
in  greatest  abundance,  that  the  first  and  principal  operations  of 
digestion  take  place,  and  that  from  this  part  the  food  is  gradual- 
ly propelled  towards  the  small  end,  becoming  more  completely 
changed  during  its  progress. 

It  appears  from  the  experiments  of  Dr.  Beaumont  on  an  indi- 
vidual, who  lived  many  years  with  a  fistulous  opening  into  the 
stomach,  which  allowed  the  contents  of  that  organ  to  be  at  all 
times  examined,  that  the  different  kinds  of  aliment  all  require  to 
undergo  the  chemical  action  of  the  gastric  juice  in  order  to  be 
reduced  to  the  state  of  chyle  ;  but  that  the  rapidity  of  this  pro- 
cess differs  considerably,  according  to  the  deUcacy  of  the  natural 
texture  of  the  food,  and  the  extent  of  its  previous  mechanical 
division.  Animal  substances  are  found  to  be  more  rapidly  con- 
verted into  chyme  than  vegetable  ;  and  oily  substances,  although 
containing  a  large  proportion  of  nutritious  elements,  are  compara- 
tively difficult  of  digestion.* 

Some  curious  evidence  was  afforded  by  Dr.  Roget  and  Dr.  P. 
M.  Latham,  on  the  occasion  of  an  epidemic  scurvy  which  pre- 
vailed in  the  years  1823  and  1824,  among  the  prisoners  in  the 
Milbank  Penitentiary,  that  too  liquid  a  diet,  consisting  of  too 
large  a  proportion  of  soups,  although  abundantly  supplied,  did 
not  furnish  sufficient  nourishment  for  the  preservation  of  health; 
probably  from  their  not  being  retained  in  contact  with  the  coats 
of  the  stomach  during  the  time  requisite  for  their  underg'oing  the 
process  of  digestion.f 

350.  A  great  number  of  hypotheses  were  devised  by  the  older 
physiologists  in  order  to  explain  the  process  of  digestion.  These 
we  shall  only  briefly  enumerate,  without  engaging  in  any  laboured 
refutation  of  what,  in  the  present  advanced  state  of  science,,  does 
not  recjuire  much  examination  to  prove  the  fallacy.  The  ancients 
had  generally  adopted  the  opinion  of  Hippocrates,  which  was 

*  [From  his  experiments  on  this  individual,  Dr.  Beaumont  inferred,  that 
pig's  feetsoused,  rice,  and  tripe  soused,  were  soonest  senton  into  the  duodenum? 
but  it  need  scarcely  be  said,  that  all  such  tabular  results  apply,  in  strictness,  to 
the  individual  concerned  only;  yet  they  afford  useful  comparative  views,  which,, 
with  exceptions  depending;  upon  individual  peculiarities,  may  be  regarded  as 
approximations  applicable  to  mankind  in  general'. — Beaumont,  Op.  di. 

Dr.  Beaumont's  table  has  been  copied^ — and  a  column  indicating  the  ratio  of 
the  digestibility  of  the  various  articles  added — in  l)iingliso7i^s  Elements  of  Hy- 
giene, p.  233,  Philad.,  1835,  and  in  his  Medical  Dictionary,  2d  edit.  Philad. 
1839,  art.  Digestible.  See  also.  Combe's  Physiology  of  Digestion,  Amer. 
ed.  New  York,  1836.] 

■j-  See  an  account  of  the  disease  lately  prevalent  in  the  General  Penitentia- 
ry.    By  P.  M.  Latham.  M.  D.     Loudon,  1825. 


164  NUTRITIVE    FUNCTIONS. 

enforced  by  Galen,  that  the  food  was  digested  by  what  was 
called  a  process  of  concoction.  This,  however,  seems_to  be  only 
another  term  for  digestion,  instead  of  affording  any  explanation 
of  its  nature.  Some  physiologists  considered  digestion  as  result- 
ing from  a  degree  of  putrefaction ;  a  process  which  is  in  reahty 
of  a  totally  opposite  nature,  although  agreeing  in  some  minor 
points,  such  as  the  breaking  down  of  the  cohesion  of  the  particles, 
and  the  occasional  disengagement  of  gas..  Others,  reasoning 
from  the  analogy  of  the  stomachs  of  granivorous  birds,  which 
are  provided  with  a  strong  muscular  apparatus  for  the  purpose 
of  grinding,  conceived  that  a  similar  process  took  place  in  the 
human  stomach,  and  that  digestion  was  the  effect  of  mechanical 
trituration.  But  the  experiments  of  Stevens  and  Spallanzani,  the 
results  of  which  have  been  already  stated,  are  alone  sufficient  to 
overturn  this  hypothesis. 

351.  The  earher  chemical  physiologists  ascribed  digestion  to 
a  species  of  fermentation.  This  term,  however,  appears  to  have 
been  misapplied,  in  as  far  as  digestion  is  conceived  to  be  identi- 
cal with  either  the  acetous  or  vinous  fermentatipn ;  and  if  it  were 
meant  to  convey  the  idea  of  a  peculiar  species  of  chemical  change 
taking  place  in  the  stomach,  and  in  no  other  situation,  then  no- 
thing is  gained  by  the  substitution  of  the  term  ernployed  for  that 
of  digestion,  which  must  express  precisely  the  same  idea.  More 
modern  writers  have  imagined  they  were  giving  an  explanation 
of  the  phenomena  of  digestion,  by  referring  them  simply  to  the 
action  of  the  vital  principle,  or  the  vital  powers,  or  the  prin- 
ciple of  life,  or  by  whatever  name  they  chose  to  designate  an 
imaginary  agent  which  gave  rise  to  all  those  phenomena,  not 
referable  either  to  mechanical  or  chemical  principles.  But  after 
the  remarks  we  have  elsewhere  made  on  this  radical  error  of 
substituting  final  for  physical  causes,  and  of  prematurely  general- 
izing the  principles  which  actuate  the  living  system,  it  is  needless 
farther  to  insist  upon  the  fallacy  of  this  mode  of  reasoning. 

352.  A  doctrine  has  lately  been  advanced,  with  greater  sem- 
blance of  truth,  that  digestion  is  essentially  a  nervous  function  ; 
that  is,  one  which  is  directly  dependent  on  nervous  power.  A 
variety  of  facts  unquestionably  prove  that  the  functions  of  the 
stomach  are  very  much  influenced  by  the  states  of  the  nervous  sys- 
tem. The  section  of  the  par  vagum,  or  eighth  pair  of  nerves,  in  the 
neck  of  an  animal,  is  followed  by  the  almost  total  interruption 
of  digestion;  whence  we  may  infer  that  the  influence  conveyed 
by  these  nerves  is  necessary  both  for  the  secretion  of  the  gastric 
juice,  and  perhaps  also  for  the  muscular  actions  of  the  stomach. 
It  is  exceedingly  remarkable,  however,  that  where  the  galvanic 
influence  is  sent  through  the  mutilated  nerves,  by  means  of  a 
voltaic  battery,  digestion  maybe  renewed,  and  goes  oil  for  a  con- 
siderable time;  whence  it  has  been  inferred  by  Dr.  W.  Philip, 


CHYLIFICATION.  16& 

that  the  nervous  power,  or  the  agency  which  is  conveyed  through 
the  nerves,  and  which  influences  secretion,  is  itself  identical  with 
the  electric  or  galvanic  fluid.* 

353.  The  pyloric  orifice  of  the  stomach  is  furnished  with  a 
circular  bund  of  fibres,  covered  by  a  fold  of  the  nervous  coat; 
and  acting  as  a  sphincter  muscle,  which  closes  the  passage 
during  the  earlier  stages  of  digestion,  so  as  not  to  suffer  the 
escape  of  the  food  until  it  has  undergone  the  requisite  changes 
which  constitute  its  digestion.  The  aliment  is  conveyed  to  the 
pylorus  in  proportion  as  it  has  undergone  these  changes.  There 
appears  to  exist  in  this  part  of  the  stomach  a  peculiar  and  ex- 
tremely delicate  sensibility,  and  a  power  of  selecting  those  por- 
tions of  the  food  that  are  properly  digested,  and  of  allowing 
them  to  pass,  while  those  which  are  undigested  are  retained  in 
the  stomach. 

A  portion  of  aliment  often  passes,  however,  unchanged  through 
the  pylorus  along  with  the  chyme.  We  observe,  for  instance, 
that  many  hard  substances,  such  as  the  stones  of  cherries  and 
plums,  find  their  way  through  the  pylorus  without  much  diffi- 
culty. The  seeds  of  many  plants  are  only  softened  by  their 
detention  in  the  stomach,  and  passing  with  no  other  change 
through  the  intestinal  canal,  are  prepared  for  germination  in  the 
soil  to  which  they  may  be  transferred.  Thus  many  species  of 
plants  and  trees  have  been  known  to  grow  at  places  very  remote 
from  each  other  in  consequence  of  their  seeds  having  been  con- 
veyed by  birds  that  had  swallowed  them. 


CHAPTER    VIT. 


CHYLIFICATlOiV. 


354.  The  aliment,  now  converted  by  the  process  of  digestion 
into  chyme,  after  passing  the  pylorus,  enters  into  the  duodenum, 
which  is  the  first  of  the  small  intestines.  In  the  duodenum  the 
chyme  undergoes  further  changes,  which  are  quite  as  great  and 

*[  Dr.  Prout  {Bridgewater  Treatise,  Amer.  edit.  p.  268,  Philad.  1834) 
conceives,  that  tlie  source  of  the  muriatic  acid  in  the  stomach  is  the  common 
salt  existinnj'  in  the  blood,  which  he  conceives  is  decomposed  by  sjalvanic 
'  agency  ;  and  Drs.  Purkinje  and  Pappenheim  (^M idler'' slrclilv.  1838,  and  British 
and  Foreign  Med.  Rev.  Oct.  1838,  p,  527)  announce  a  similar  opinion.  From 
their  galvanic  experiments,  they  think  it  results,  that  the  juices  mixed  with 
the  food  in  the  natural  way, — the  saliva,  the  mucus,  and  the  portions  of  chloride 
of  sodium  generally  present  therein;  and  still  more,  the  gastric  mucous  mem- 
brane itself, — develop  as  much  chlorine  as  is  required.] 


16G  NUTRITIVE    FUNCTIONS. 

as  essential  to  its  proper  assimilation,  as  those  which  the  food 
experienced  in  the  stomach,  and  they  are  at  the  same  time  in- 
volved in  equal  obscurity.  Almost  all  that  is  known  respecting 
the  nature  of  these  changes,  is,  that  soon  after  the  chyme  has 
been  received  into  the  intestines,  it  begins  to  separate  into  two 
parts;  the  one  a  white  milky  fluid,  which  is  termed  the  chyle; 
and  the  other,  residual  matter,  which  afterwards  becomes /ceces, 
and  is  eventually  ejected  from  the  body. 

355.  Previously  to  our  examining  the  processes  by  which  this 
separation  is  effected,  it  will  be  proper  to  consider  the  chemical 
properties  of  the  chyle. 

1.  Properties  of  Chyle. 

356.  Chyle  is  the  fluid  which  is  prepared  from  the  food  taken 
into  the  stomach,  and  which,  being  the  last  process  of  digestion, 
is  formed  in  the  intestinal  canal.  It  is  only  of  late  years  that  we 
have  acquired  any  accurate  knowledge  of  its  chemical  proper- 
ties. It  is  evident  that  experiments  on  this  fluid  can  only  be 
instituted  on  quadrupeds,  and  that  it  is  only  by  reasoning  from 
analogy  that  we  can  extend  the  knowledge  so  obtained  to  the 
human  economy.  If  chyle  be  taken  from  the  thoracic  duct  of 
an  animal  a  few  hours  after  it  has  taken  food,  it  has  very  much 
the  appearance  of  cream,  being  a  thick  fluid  of  an  opaque  white 
colour,  without  smell,  and  having  a  slightly  acid  taste,  accom- 
panied by  a  perceptible  sweetness.  It  restores  the  blue  "colour  of 
litmus,  previously  reddened  by  acetic  acid ;  and  appears,  there- 
fore, to  contain  a  predominance  of  alkali.  When  subjected  to 
microscopic  examination,  chyle  is  found  to  contain  a  multitude 
of  globules,  of  smaller  diameter  than  those  of  the  blood,  and  cor- 
responding in  size  and  appearance  to  those  of  milk.  In  about  ten 
minutes  after  it  is  removed  from  the  thoracic  duct,  it  coagulates 
into  a  stiff  jelly,  which  in  the  course  of  twenty-four  hours  sepa- 
rates into  two  parts,  producing  a  firm  and  contracted  coagulum, 
surrounded  by  a  transparent  colourless  fluid. 

357.  The  coagulated  portion,  according  to  Vauquelin,  is  a 
substance  of  a  nature  intermediate  between  albumen  and  perfect 
fibrin,  marking  the  transition  from  the  one  to  the  other.  It  has 
perhaps,  indeed,  a  closer  resemblance  to  the  caseous  part  of  milk 
than  to  fibrin.  It  is  rapidly  dissolved  both  by  pure  and  sub- 
carbonated  alkalies,  forming  pale  brown  compounds.  Its  solu- 
tion in  ammonia  has  a  reddish  hue.  The  acids  throw  down  a 
substance  intermediate  between  fat  and  albumen,  which  an  ex- 
cess of  nitric  acid  re-dissolves  in  the  cold;  and  sulphuric,  muriatic, 
oxalic,  and  acetic  acids,  by  boiling  for  a  short  time,  also  dissolve 
it.  Diluted  sulphuric  acid  also  very  readily  effects  its  solution. 
Very  dilute  nitric  acid   gradually  converts  it  into  adipocire ; 


CHYLIFICATION.  167 

when  the  acid  is  more  concentrated,  the  coagukim  assumes  the 
appearance  of  gelatin ;  and  when  heat  is  applied,  oxalic  and 
carbonic  acids  are  evolved.  It  is  insoluble  either  in  alcohol  or 
ether. 

358.  That  portion  of  chyle  which  retains  the  liquid  form  con- 
tains a  portion  of  albumen,  which  may  be  coagulated  by  heat, 
alcohol,  or  acids.  The  clear  liquid,  reduced  by  evaporation  to 
half  its  bulk,  deposits  crystals,  which  were  found  by  Mr.  Brande 
to  bear  a  strong  resemblance  to  those  of  sugar  of  milk. 

359.  A  few  saline  bodies,  similar  to  those  existing  in  most 
animal  fluids,  were  found  by  Dr.  Marcet,  to  be  present  in  chyle. 

360.  The  principal  ingredients  in  chyle,  are,  thepefore,  accord- 
ing to  Vauquelin,  1st,  a  large  proportion  of  albumen;  2d,  a 
smaller  one  of  fibrin;  3d,  a  fatty  substance  which  gives  to  the 
chyle  the  appearance  of  milk ;  4th,  several  salts,  such  as  carbo- 
nate of  potass,  muriate  of  potass,  and  prophosphate  of  iron. 

361.  Berzelius  is  strongly  inclined  to  distrust  the  supposed 
analogy  betvi^een  chyle  and  milk,  as  having  but  little  foundation 
in  their  real  chemical  nature. 

362.  It  would  be  exceedingly  interesting  to  ascertain  the  differ- 
ences which  exist  in  the  properties  of  chyle  taken  from  different 
orders  of  animals,  that  we  might  be  able  to  trace  the  influence  of 
different  kinds  of  food  upon  this  fluid.  Dr.  Marcet  and  Dr.  Prout 
have  made  comparative  experiments  with  this  view  upon  the 
chyle  taken  from  different  dogs,  some  of  which  were  fed  exclu- 
sively on  animal,  and  others  on  vegetable  food.  The  chyle  in  the 
former  case  was  found  to  be  much  whiter,  contained  more  solid 
matter,  and  yielded  more  albumen  than  in  the  latter.  The  general 
results  of  these  experiments  are  contained  in  the  following  table. 
Some  faint  traces  of  oily  matter  and  of  sugar  of  milk  were 
obtained,  but  in  quantities  too  minute  to  be  estimated. 


Chyle  from 
vegetable  food. 

Chyle  from 
animal  food. 

Water         -         -         93-6  <      - 

89-2 

Fibrin         -         -             -6         - 

•8 

Incipient  albumen           4-6 

4-7 

Saline  matters     -             -8         - 

•7* 

363.  When  both  kinds  of  chyle  were  submitted  to  destructive 

*  [The  difference  between  the  chyle  from  food  of  such  opposite  character  as 
indicated  by  these  results  is  trifling,  and  exhibits  the  great  uniformity  in  the 
action  of  the  agents  of  chylous  absorption.  More  recent  researches  by 
MM.  Macaire  and  Marcet  {Mem.  de  la  Societe  de  Physique,  &c.  de  Geneve,  v. 
389,)  tend,  indeed,  to  establish  the  fact,  that  the  chyle  and  the  blnod  of  her- 
bivorous and  carnivorous  quadrupeds  are  identical  in  their  composition,  in  as 
far,  at  least,  as  regards  their  ultimate  analysis.  There  must,  consequently, 
be  an  action  of  selection  at  the  very  extremities  of  the  chyliferous  vessels,  to 
occasion  this  striking  uniformity  in  the  composition  of  the  chyle.] 


168  NUTRITIVE    FUNCTIONS. 

distillation,  the  vegetable  chyle  produced  three  times  as  much 
•carbon  as  the  animal  chyle ;  the  latter,  therefore,  probably  con- 
tained a  greater  proportion  of  hydrogen  and  nitrogen.  The  chyle 
of  a  horse,  derived  of  course  from  vegetable  food  alone,  v^^as 
found  by  Vauquelin  to  be  in  a  more  animalized  state  than  that 
which  Dr.  Marcet  procured  from  dogs.  Dr.  Prout,  also,  com- 
paring the  chyle  as  prepared  from  vegetable  and  from  animal 
food,  found  the  former  to  contain  more  water  and  less  albuminous 
matter,  while  the  fibrin  and  the  salts  were  nearly  the  same  in 
both,  and  both  exhibited  traces  of  oily  matter.  On  the  whole, 
he  states  the  difference  between  the  tvvo  kinds  of  chyle  to  be  less 
considerable  than  had  been  observed  by  Dr.  Marcet.  On  tracing 
the  successive  changes,  which  the  chyle  undergoes  in  its  passage 
along  the  vessels,  he  found  that  its  resemblance  to  blood  increases 
in  each  of  these  successive  stages  of  its  progress.* 

2.  Functions  of  the  Intestines. 

364.  At  the  part  of  the  duodenum  where  the  separation  of  the' 
chyme  into  chyle  and  residual  matter  takes  place,  the  ducts  from 
the  pancreas  and  the  liver  terminate,  so  that  the  chyme  is  sub- 
jected to  the  action  of  the  secretions  from  these  two  important 
glands,  namely  the  paMc?-eaizcjMZce,  and  the  6z7e,  which  slowly 
distil  into  the  duodenum.  Sir  Benjamin  Brodie  concluded,  from 
experiments  which  he  made  upon  living  animals,  that  the  forma- 
tion of  chyle  is  the  immediate  result  of  the  admixture  of  bile  with 
the  chyme.t  In  studying  the  changes  which  occur  in  this  proi- 
cess,  it  will  be  necessary  first  to  examine  the  chemical  properties 
of  these  secretions. 

365.  The  secretion  from  the  pancreas,  which  flows  into  the 
intestine,  and  is  mixed  with  the  digested  food  almost  immediately 
on  its  exit  from  the  stomach,  has,  no  doubt,  some  share  in  the 
process  of  chylification ;  but  as  it  appears  to  be  exceedingly 
analogous,  both  in  its  sensible  properties  and  chemical  composi- 
tion, to  the  saliva,  it  is  difficult  to  understand  the  mode  of  its 
operation,  independently  of  mere  dilution.  As  it  is  found,  how- 
evef,  to  contain  a  large  quantity  of  albumen,  a  great  portion  of 
this  substance  may  perhaps  go  to  the  formation  of  chyle. 

*  Annals  of  Philosophy,  xiii.  29. 

f  [These  experiments  consisted  in  tying  the  choledoch  duct  in  animals  ; 
but  similar  experiments  by  M.  Voisin  (^Nouvel  Apercu  sur  la  Physiologie  du 
Foie,  &c.,  Paris,  1833)  show,  that  the  ligature  of  the  choledoch  duct  does  not 
prevent  the  formation  of  chyle,  provided  the  passage  of  the  pancreatic  fluid 
is  not  at  the  same  time  obstructed.  The  bile,  consequently,  although  an  im- 
portant, is  not  an  essential,  agent  in  digestion  effected  in  the  duodenum.  Bun- 
■glison''s  Physiology,  i.  539.] 


CHYLIFICATION.  160 


3.  Properties  of  Bile. 


366.  Tlie  bile,  a  secretion  prepared  by  the  liver,  is  poured  into 
the  same  part  of  the  intestine  as  the  pancreatic  juice.  Its  great 
importance  in  the  animal  economy  induced  physiologists  from  the 
earliest  times  to  pay  much  attention  to  its  chemical  properties. 
Its  analysis  has  been  attempted  by  Boyle,  Boerhaave,  and  Baglivi, 
and  more  recently  by  Fourcroy,  Cadet,  Thenard,  and  Berzelius.* 
But  it  unfortunately  happens,  that  in  several  important  particulars 
the  accounts  given  by  these  diflerent  chemists  do  not  accord 
with  one  another.  These  discrepancies,  as  Mr.  Brande  observes, 
seem  partly  to  arise  from  the  extreme  facility  with  which 
chemical  reagents  react  on  this  secretion^  so  that  many  of  the 
supposed  educts,  or  component  parts  which  have  been  enumerated 
by  different  chemists,  are  probably  products  of  the  different 
operations  to  which  it  has  been  submitted,  or,  at  all  events, 
modifications  of  its  true  proximate  elements.!  The  bile  of  the 
ox,  from  the  facility  of  preserving  it,  has  been  that  chiefly  selected 
as  the  subject  of  experiment,  and  made  the  standard  of  comparison 
with  that  of  man  and  other  animals. 

367.  The  substances  to  which  this  fluid  owes  its  specific  pro- 
perties are,  according  to  Thenard,  fi7\^t,  a  peculiar  inflammable 
resin,  soluble  in  alcohol;  secondly,  picromel,  a  substance  insoluble 
in  water  and  in  alcohol,  incapable  of  being  crystallized,  but  form- 
ing, with  resin  and  a  small  portion  of  soda,  a  triple  compound 
which  is  soluble  in  water  ;  and  it  is  in  this  state  that  it  exists  in 
bile ;  and,  thirdhj,  a  yellow  matter,  distinct  from  either  of,  the 
former.  In  addition  to  the  soda,  which  is  combined  with  the 
resin  and  picromel,  bile  contains  a  small  quantity  of  phosphate, 
muriate  ahd  sulphate  of  soda,  as  also  phosphate  of  lime,  and  a 
minute  trace  of  iron. 

368.  Berzelius  denies  the  correctness  of  the  distinctions  which 
Thenard  has  endeavoured  to  draw  between  the  three  animal 
ingredients  of  bile  above  mentioned.  He  gives  to  its  character- 
istic principle,  the  name,  of  biliary  matter;  and  describes  it  as 
being  of  a  resinous  nature,  and  precipitable  by  acids ;  the  preci- 
pitate, or  pier 07nel,  or  the  gallenstoff  o{  Berzelius,  being  a  com- 
pound of  the  acid  employed  and  this  biliary  matter.  According 
to  Thenard,  human  bile  differs  from  that  of  the  ox  chiefly  in 

*  [The  latest  analysis  is  by  Muratori  (Bulletino  Medicke  di  Bologna,  p.  160, 
Agosto  et  Settembre,  1836.)  He  assigns  it  the  following  constituents : — 
Water  832  ;  peculiar  fatty  matter  5  ;  colouring  matter  11  ;  cholesterine  com- 
bined with  soda,  4;  picromel  of  Thenard,  94*86;  extract  of  meat  {^Estratto 
di  Came)  2-69  ;  mucus,  37  ;  soda,  5'14  ;  phosphate  of  soda,  3*45  ;  phosphate 
of  lime,  3;  and  chloruret  of  sodium,  1.86.) 

f  Cyclopaedia  of  Anat.  and  Phys.,  art.  Bile. 

15 


170  NUTRITIVE    FUNCTIONS. 

containing  no  picromel.     M.  Raspail  considers  bile  to  be  essen- 
tially a  saponaceous  substance,  with  a  base  of  soda.* 

369.  The  peculiar  matter  of  hile  is  found  in  the  residual  matter, 
and  does  not  enter  into  the  composition  of  chyle.  The  chief 
uses  of  the  bile  appear  to  be  those  of  a  chemical  agent,  promoting 
the  decomposition  of  the  chyme,  and  also  stimulating  the  secre- 
tion of  mucus,  and  the  peristaltic  motion  of  the  intestines. 
Digestion  may,  however,  go  on  to  a  certain  degree,  and  imper- 
fectly, although  the  flow  of  bile  into  the  intestines  be  entirely 
prevented. 

4.  Functions  of  the  Small  Intestines. 

370.  Professors  Tiedemann  and  Gmelin  found,  from  their  expe- 
riments, that  the  upper  part  of  the  small  intestines  contains  a 
considerable  quantity  of  uncombined  acid,  which  is  principally 
the  acetic,  mixed  with  a  little  butyric,  and  rarely  with  the  mu- 
riatic. On  proceeding  to  the  lower  parts  of  the  small  intestines, 
they  found  the  fluids  had  alkaline  instead  of  acid  properties.  This 
gradual  disappearance  of  acid  is  probably  in  part  the  effect  of 
its  neutralization  by  the  free  alkali  contained  in  the  bile.  The 
following,  according  to  these  physiologists,  are  the  changes 
which  take  place  in  the  contents  of  the  small  intestines.  The 
chyme,  which  is  acid,  mixes  with  the  bile,  the  pancreatic  juice, 
and  the  mucous  secretion  from  the  coats  of  the  intestine.  The 
muriatic  acid  combines  with  the  soda  of  the  bile,  and  at  the  same 
time  disengages  from  it  the  acetic  or  carbonic  acids  with  which 
it  had  been  previously  united.  It  also  separates  the  mucus  and 
cholesterine  of  the  bile  in  the  form  of  white  flakes,  which  have 
often  been  mistaken  for  chyle.  The  pancreatic  juice  and  the 
intestinal  mucus  contribute,  in  some  unknown  manner,  to  this 
effect.  The  chemical  changes  are  promoted,  and  the  contents 
of  the  intestines  successively  propelled  forwards  along  the  whole 
tract  of  the  canal,  by  the  peristaltic  actions  of  the  muscular  coat, 
the  effects  of  which  are  analogous  to  those  we  have  already 
described  as  taking  place  from  a  similar  action  in  the  stomach. 

5.  Function  of  the  Spleen. 

371.  It  is  probable  that  the  spleen  is  an  organ  subservient  to 
some  purpose  connected  with  digestion ;  but  what  that  precise 
purpose  can  be  is  a  question  involved  in  great  obscurity.  A  vast 
number  of  hypotheses  and  conjectures  have  been  hazarded  on 
this  subject ;  but  they  are,  for  the  most  part,  devoid  of  even  the 

*  [This  was  the  view  of  Cadet,  upwards  of  seventy  years  ag^o — Experi- 
ences siiM'  la  Bile  des  Hommes^  &c,  in  Memoir,  de  I'Academ.  de  Paris,  1767.] 


CHYLIFICATION.  171 

slightest  probability.  Any  theory  that  assigns  a  very  important 
office  to  the  spleen  will  be  overturned  by  the  fact,  that  in  many 
animals  the  removal  of  this  organ,  far  from  being  fatal,  or  inter- 
rupting in  any  sensible  manner  the  continuance  of  the  functions, 
seems  to  be  borne  with  perfect  impunity.  Sir  E.  Home  has  ad- 
vanced an  opinion,  for  which  there  appears  to  be  some  proba- 
bility, namely,  that  the  spleen  serves  as  a  receptacle  for  any 
superfluous  quantity  of  fluid  taken  into  the  stomach,  and  which, 
if  not  removed,  might  interfere  with  the  regular  process  of  diges- 
tion. This  excess  he  supposes  is  transmitted  directly  to  thq 
spleen  by  communicating  vessels,  and  lodged  there  until  it  is 
gradually  removed,  partly  by  the  veins,  and  partly  by  the  ab- 
sorbents. 

372.  It  appears,  indeed,  from  the  observations  of  Bichat,  Leu- 
ret,  Lassaigne,  and  others,  that  during  digestiori,  and  even  after 
copious  draughts  of  liquids,  the  vessels  of  the  spleen  become  ex- 
ceedingly turgid  with  blood.  Hence  the  opinion  has  arisen,  that 
the  chief  use  of  the  spleen  is  to  relieve  the  stomach  and  intes- 
tines from  that  congestion  which  would  otherwise  take  place  in 
their  blood-vessels  during  digestion.  The  very  vascular,  ap- 
proaching to  a  cellular  structure  of  the  spleen,  which  very  readily 
admits  of  dilatation,  would  seem  to  countenance  this  hypothesis.* 

6.  Functions  of  the  Large  Intestines. 

373.  The  functions  of  the  large  intestines  are  not  confined  to 
the  mere  conveyance  and  expulsion  of  feculent  matter,  altjiough 
the  exact  nature  of  the  changes  which  take  place  in  their  con- 
tents, and  the  subserviency  of  those  changes  to  the  object  of 
nutrition,  have  never  been  clearly  determined.  It  would  appear 
that  some  important  changes  are  effected  in  that  enlarged  por- 
tion of  the  canal  which  is  termed  the  coicum,  and  which  has  by 
some  been  regarded  as  a  kind  of  supplementary  stomach,  in 
which  fresh  chyme  is  formed,  and  fresh  nutriment  extracted  from 
the  materials  that  have  passed  through  the  small  intestines.  This 
chymous  product  is  supposed  to  be  converted,  as  in  the  former 
case,  into  a  species  of  chyle,  which,  from  containing  a  greater 
proportion  of  oil,  bears  a  resemblance  to  fat,  and  is  in  this  state 
absorbed  from  the  inner  surface  of  the  great  intestines.  The 
capability  of  the  great  intestines  to  extract  nourishment  from 
their  contents  is  proved  by  the  fact,  that  nutritious  matter  inject- 
ed into  them  has  been  known  to  support  life  for  a  certain  time, 
and  also  from  their  being  able  to  eilcct  the  coagulation  of*  milk.' 

*  [One  of  the  latest  views  is  that  of  MM.  Tiedemann  and  Gmelin,  who 
regard  the  spleen  as  a  ganglion  of  the  absorbent  system,  which  prepares  a 
fluid  to  be  mixed  with  the  chyle  to  effect  its  animalization  ;  thus  regarding  its 
functions  to  be  identical  with  those  of  the  mesenteric  glands.] 


172  NUTRITIVE    FUNCTIONS. 

374.  A  certain  quantity  of  gas  is  almost  constantly  present  in 
the  intestinal  canal,  and  often  also  in  the  stomach.  Magendie 
and  Chevreul,  who  have  analysed  these  gases,  found  that  what 
the  stomach  contained  consisted  of  a  mixture  of  oxygen  and 
nitrogen;  but  that  in  the  lower  intestines  the  oxygen  had  wholly 
disappeared,  as  also  a  great  part  of  the  nitrogen,  and  that,  in- 
stead of  these,  the  component  parts  of  the  gas  were  carbonic 
acid,  hydrogen,  carburetted  hydrogen,  and  a  little  sulphuretted 
hydrogen. 

375.  The  time  required  for  the  completion  of  the 'processes 
we  have  described  as  taking  place  in  the  stomach,  the  small,  and 
the  large  intestines,  varies  much,  not  only  according  to  the 
nature  of  the  food,  but  according  to  the  conditions  of  the  organs 
and  of  the  general  health,  and  to  constitutional  peculiarities. 
The  digestion  of  food  in  ttie  stomach  is  usually  considered  as 
requiring  three  or  four  hours.  Animal  food  is  longest  retained, 
and  undergoes  the  greatest  alteration  in  the  stomach.  Vegetable 
food,  on  theother  hand,  passes  more  quickly  and  with  less  altera- 
tion, out  of  the  stomach,  and  undergoes  more  change  in  the 
intestines  than  animal  food. 


Sect.  VIII. — Lacteal  Absorption. 

376.  The  chyle,  which  has  been  prepared  in  the  duodenum, 
and  along  the  whole  course  of  the  small  intestines,  in  the  man- 
ner we  have  described,  is  received  by  absorption  into  the  lacteals, 
and  by  them  conveyed  to  the  thoracic  duct,  which  transmits  it 
to  the  great  veins  in  the  vicinity  of  the  heart.  The  lacteal  ves- 
sels may  be  considered  as  forming  part  of  the  great  system  of 
absorbents  which,  as  we  shall  afterwards  find,  are  extensively 
distributed  throughout  the  body.  We  shall  therefore  reserve 
their  description  until  a  general  account  is  given  of  this  system, 
in  treating  of  the  function  of  absorption  generally. 

377.  The  discovery  of  the  lacteals  was  made  in  the  year  1622 
by  Aselli,  in  the  mesentery  of  a  dog,  which  he  bad  killed  a  few 
few  hours  after  the  animal  had  made  a  plentiful  meal.  Their 
termination  in  the  thoracic  duct  was  discovered  by  Pecquet  in 
1651.  They  originate  by  open  mouths  from  the  villi  of  the  inner 
coat  of  the  small  intestines,  in  the  form  of  very  minute  tubes, 
which  soon  unite  into  one  common  vessel  proceeding  from  each 
of  the  villi ;  and  these  vessels  afterwards  joining  successively 
form  larger  and  larger  branches,  which  ascend  along  the  mesen- 
tery, generally  following  the  course  of  the  veins,  till  they  are 
collected  at  the  root  of  the  mesentery,  and,  after  passing  through 
numerous  glands,  terminate  at  the  lower  end  of  the  thoracic  duct, 


LACTEAL    ABSORPTION.  173 

where  there  is  aa  enlargement  which  has  been  called  the  reccpta- 
culum  chyl.i. 

378.  Uncertainty,  however,  still  exists  respecting  the  minute 
anatomy  of  the  lacteals,  at  their  origin  from  the  intestine,  many 
anatomists  having  in  vain  sought  for  the  appearances  above 
described.  Their  open  orifices  can  only  be  seen  when  the  lac- 
teals are  distended  with  chyle,  and  they  are  more  readily  detected 
in  fishes  where  they  have  no  valves,  and  where  therefore  the 
branches  admit  of  being  injected  from  their  trnnks.*  Their 
coats,  although  thin  and  perfectly  transparent,  yet  possess  con- 
siderable strength,  so  as  to  allow  of  being  distended  by  injections 
without  being  ruptured  ;  and  even  afford  decisive  indications  of 
having  the  power  of  contracting  and  propelling,  forwards  their 
contents.'  The  utility  of  the  numerous  valves  with  which  they 
are  provided  in  every  part  of  their  course,  in  preventing  any 
retrograde  motion  of  the  fluid  they  transmit,  is  sufficiently 
obvious. 

379.  The  power  by  which  the  chyle  is  made  to  enter  the  open 
orifices  of  the  lacteals,  is  by  no  means  easily  determined.  It  has 
been  referred  generally  to  capillary  attraction.  But  the  applica- 
tion of  the  laws  wdiich  govern  the  ascent  of  fluids  in  rigid  inor- 
ganic tubes,  to  the  elastic  vessels  of  the  living  system,  is  liable 
to  much  fallacy.  The  phenomena  appear  to  indicate  that  the 
lacteals  exercise,  in  the  exclusive  absorption  of  chyle,  a  power 
of  selection  somewhat  analogous  to  that  of  chemical  or  electric 
attraction.  It  has  been  supposed,  accordingly,  that  there  is  a 
specific  attraction  between  chyle  and  the  lacteal  vessels,  which 
causes  that  fluid  to  enter  into  them;  while  other  fluids  which  are 
presented  to  the  same  vessels  are  rejected.  This  obscure  subject 
has  given  rise  to  various  speculations,  which  are  more  curious 
and  ingenious  than  leading  to  any  satisfactory  conclusion.  It  is 
now  generally  agreed  among  physiologists,  that  the  power  which 
the  lacteals  pos'sess  of  admitting  the  absorption  of  extraneous 
substances,  if  it  exist  at  all,  is  exceedingly  hmited,  and  is  exerted 
only  on  rare  occasions. 

Various  experim.ents  made  on  animals  fully  warrant  the  con- 
clusion, that  by  far  the  greater  portion  of  the  nutritive  matter 
imparted  to  the  system  is  conveyed  into  the  blood-vessels  through 
the  channels  we  have  been  describing,  namely,  the  lacteals  and 
the  thoracic  duct.  On  the  other  hand,  there  appears  to  be  evidence 
that  a  large  portion  of  the  thinner  fluids  received  into  the  stomach 
passes  at  once  into  the  veins  by  the  immediate  absorption  of  these 
veins ;  for  they  always  disappear  rapidly  from  the  stomach,  in 
whatever  quantity  they  are  introduced.     It  is  probable  also,  that 

*  [The  doptrine  of  open  mouths  has  been  contested  by  Mascatrni,  Rudol- 
phi,  Meckel,  Mojon  and  others,  and  it  must  be  admitted,  that  we  know  nothing 
definite  regarding  the  extreme  radicles  of  the  lacteal  or  chyliferous  vessels,] 

15* 


174  NUTRITIVE    FUNCTIONS. 

some  admixture  of  tte  contents  of  the  lacteals  with  those  of  the 
blood-vessels  takes  place  in  the  mesenteric  glands,  and  that  part 
of  the  chyle  finds  its  way  into  the  mesenteric  veins  by  more  direct 
channels  than  that  of  the  general  circulation. 

380.  An  elaborate  series  of  experiments  was  undertaken  by 
Tiedemann  and  Gmelin,  with  a  vievv^  to  ascertain  whether  there 
exists  any  direct  communication  between  the  digestive  cavities 
and  the  blood-vessels,  exclusive  of  the  known  channel  through 
the  lacteals  and  thoracic  duct.  The  experiments  consisted  in 
mixing  with  the  food  of  certain  animals  various  odorous,  colour- 
ing, and  saline  materials,  the  presence  of  which  might  be  easily 
detected  by  their  appearance,  odour,  and  other  sensible  or  chemical 
properties  ;  and  in  comparing,  after  a  proper  interval  of  time,  the 
state  of  the  chyle  with  that  of  the  blood  in  the  mesenteric  veins. 
The  odorous  substances  employed  were  camphor,  musk,  alcohol, 
oil  of  turpentine,  and  assafoetida.  These  were  generally  disco- 
vered to  have  found  their  way  into  the  system,  by  their  being 
detected  in  venous  blood,  in  the  urine,  but  not  in  the  chyle.  The 
colouring  matters  were  sap-green,  gamboge,  madder,  rhubarb, 
alkanet,  and  Htm  us  ;  these  appeared.  Tor  the  most  part,  to  be  car- 
ried off  without  being  absorbed  ;  while  the  salts,  namely  potass, 
the  sulphate  and  the  prussiate  of  potass,  muriate  of  barytes, 
muriate  and  sulphate  of  soda,  acetate  of  lead  and  of  mercury,  and 
prussiate  of  mercury,  were  less  uniform  in  their  course.  A  con- 
siderable portion  of  them  seemed  to  be  rejected,  while  many  of 
them  were  found  in  the  urine,  several  in  the  venous  blood,  and  a  very 
few  only  in  the  chyle.  Hence  the  authors  conclude,  that  the  odo- 
rous and  colouring  substances  never  pass  into  the  lacteals,  and  that 
saline  bodies  do  so  occasionally  only,  or  perhaps  incidentally ;  the 
w^hole  of  them  are,  however,  found  in  the  secretions,  and  they 
must,  therefore,  have  entered  into  the  circulation  by  some  other 
channel  than  the  lacteals.* 

381.  There  appears  not,  as  far  as  we  know,  to  be  any  thing 
specific  in  the  action  of  the  thoracic  duct,  which,  as  it  appears, 
transmits  its  contents  into  the  subclavian  vein,  as  it  receives  it 
from  the  absorbents. 


Sect.  IX. — Sanguification. 

382.  The  chyle  consists,  as  we  have  seen,  of  alimentary 
matter,  reduced  to  a  certain  state,  which  may  be  regarded  as  the 
first  stage  of  animalization,  having  already  made  a  near  approach 

m 
*  Edin.  Med.  Journal,  xviii.  p.  455,  &c.     The  above  analysis  ;.of  these  ex- 
periments is  that  given  by  Dr.  Bostock  in  his  worli  on   Physiology,  p.  617, 
note. 


SANGUIFICATION.  175 

to  the  nature  of  that  blood  into  vviiich  it  is  afterwards  to  be  con- 
verted. This  conversion  of  chyle  into  blood  takes  place  after  its 
introduction  into  the  sanguiferous  system  of  vessels,  and  while  it 
passes  round  in  the  course  of  circulation.  During  this  course,  it 
necessarily  traverses  the  minute  vessels  of  the  lungs,  where  it  is 
subjected  to  the  chemical  action  of  atmospheric  air,  and  its  con- 
stituents gradually  acquire  the  characteristic  properties  which 
they  possess  as  the  ingredients  of  the  blood.  The  chief  changes 
experienced  are,  first,  that  the  fibrin  of  the  chyle  obtains  a 
greater  cohesive  tendency,  and  a  power  of  spontaneous  coagula- 
tion; and,  secondly,  that  the  white  globules  of  the  chyle  receive 
an  addition  of  red  colouring  matter,  and  are  invested  with  an 
external  vesicle,  by  which  their  size  is  increased.  But' in  order 
correctly  to  estimate  their  changes,  it  will  be  necessary  to  take 
a  general  review  of  the  chemical  and  other  physical  properties 
of  the  blood. 

383.  The  nature  and  properties  of  the  blood  have  attracted  a 
verv  large  share  of  the  attention  of  physiologists  in  all  ages;  and 
immense  labour  has  been  devoted  to  the  investigation  of  its  che- 
mical constitution. 

384.  When  examined  immediately  on  its  being  drawn  from 
the  vessels,  the  blood  appears  as  a  smooth  and  homogeneous 
fluid,  of  an  unctuous  adhesive  consistence,  of  a  slightly  saline 
taste,  and  of  a  specific  gravity  somewhat  exceeding  that  of 
water.  It  exhales  a  vapour  which  has  a  peculiar  smell  -,  but 
which,  when  condensed  and  collected,  affords  a  liquor  not  differ- 
ing sensibly  from  water.  Much  importance  was  formerly 
ascribed  to  this  vapour,  which  was  dignified  with  the  name  of 
Halitus. 

As  the  blood  does  not  preserve  the  same  consistence  at  differ- 
ent times,  its  density  is  hable  to  variation.  Haller  states  the 
specific  gravity  of  human  blood  to  be  at  a  medium,  1.0527.  Dr. 
Milne  Edwards  says  that  it  varies  from  1.052  to  1.057.  Dr.  Davy 
states  that  the  specific  gravity  of  arterial  blood  is  1.049,  and  of 
venous  blood,  1.051.  Although  it  appears  homogeneous,  it  is 
found  by  microscopical  examination  to  contain  a  large  proportion 
of  minute  globular  particles,  difilised  through  a  liquid. 

385.  In  a  few  minutes  alter  its  removal  from  the  body,  a  thin 
film  appears  on  the  surface,  and  after  a  short  time,  which  on  an 
average  is  about  seven  minutes,  the  whole  mass  becomes  cohe- 
sive, and  what-is  termed  its  coagulation  has  taken  place.  After 
it  has  remained  for  some  time  in  this  gelatinous  state,  a  separa- 
tion of  the  mass  into  two  distinct  parts  gradually  takes  place.  A 
yellowish  liquid  oozes  out  from  beneath  the  surface  of  the  mass, 
and  at  length  the  whole  is  resolved  into  a  clot,  or  solid  portion 
of  a  dark  red  colour,  which  is  called  the  crassamentum,  or  cruor, 
and  consists  chiefly  of  fibrin,  and  a  yellowish  liquid  called  the 


176  NUTRITIVE    FUNCTIONS. 

serum.  The  proportion  between  these  two  parts  has  been  vari- 
ously estimated;  and  does  not  indeed  admit  of  accurate  deter- 
mination, from  its  being  variable  in  itself  under  different  circum- 
stances. On  an  average,  it  may  be  stated  that  the  crassamentum 
amounts  to  about  one-third  of  the  weight  of  the  serum.  Dr. 
Scudamore  and  Mr.  Wood  found,  however,  by  taking  the  mean 
of  twelve  experiments,  that  the  crassamentum  amounted  to 
53.307  per  cent.  The  period  at  which  coagulation  begins  and  is 
completed,  varies  not  only  with  the  condition  of  the  blood  itself, 
but  also  with  the  circumstances  in  which  it  is  placed.  It  com- 
mences sooner  as  the  vessel  is  more  shallow ;  but  on  an  average 
it  may  be  said  to  begin  in  about  three  or  four  minutes,  and  to  be 
completed  in  seven  or  eight.  But  the  contraction  of  the  coagulum 
continues  for  a  long  time  after,  and  sometimes  does  not  cease 
till  the  fourth  Hay.  It  does  not  appear  that  the  specific  gravity 
of  the  blood  is  sensibly  altered  during  its  coagulation. 

386.  Great  difference  of  opinion  has  existed  as  to  the  occur- 
rence of  a  change  of  temperature  during  this  process  of  coagula- 
tion. The  analogy  of  other  instances  in  which  the  conversion  of 
a  fluid  into  a  solid  is  accompanied  with  the  evolution  of  heat,  has 
induced  many  to  think  that  a  similar  effect  attends  the  coagula- 
tion of  the  blood.  Fourcroy  seated,  that  a  rise  of  temperature 
actually  takes  place  ;  but  Hunter  on  the  contrary,  produced  facts 
leading  to  an  opposite  conclusion.  The  result  obtained  by  Four- 
croy has,  however,  been  confirmed  by  the  experiments  of  Dr. 
Gordon,  who  found  that  the  coagulating  portion  of  a  quantity  of 
blood  was  warmer  than  the  rest  by  about  six  degrees.  On  re- 
peating the  experiment  on  blood  drawn  from  a  patient  labouring 
under  inflammatory  fever,  the  .rise  of  the  thermometer  was  no 
less  than  twelve  degrees.  Subsequent  researches  by  Dr.  John 
Davy,  have,  however,  thrown  considerable  doubt  upon  the  accu- 
racy of  the  above  conclusion,  by  pointing  out  some  sources  of 
fallacy  in  the  investigation  of  Dr.  Gordon.  Dr.  Scudamore,  on 
the  other  hand,  found  that  heat  was  produced  during  coagulation, 
but  to  a  less  degree.*  Vogel  and  Brande  have  ascertained  that 
carbonic  acid  gas  is  disengaged  ;  and  this  appeared  to  happen  to 
an  unusual  extent  in  blood  drawn  soon  after  a  meal.f 

387.  The  coagulation  of  the  blood  is  a  phenomenon  not  strictly 
analogous  to  any  other  with  which  we  are  acquainted,  and  has 
never  been  satisfactorily  explained.     The  operation  of  external 

*  [The  discrepancy  of  observers  on  this  subject  is  great.  Mr.  Thackrah 
and  Schroder  van  der  Kolli,  accord  with  Mr.  Hunter  in  the  belief,  that  the 
increase  of  temperature  from  this  cause  is  very  slight,  or  null,  whilst  Raspail 
asserts,  that  the  temperature  falls  !] 

I  [A  similar  discrepancy  exists  on  this  point.  Neither  Dr.  John  Davy, 
nor  Dr.  Duncan,  junr..  nor  Dr.  Christison,  could  procure  it  during  the  coaiju- 
lation  of  the  blood.  Yet  there  is  no  doubt,  that  the  blood  contains  carbonic 
acid.     See,  on  all  this  subject,  Dunglison's  Physiology,  ii.  54.] 


SANGUIFICATION.  177 

agents  upqn  it  is  not  so  well  marked  as  to  enable  ns  to  refer  it  to  any- 
general  operation  of  the  physical  properties  of  matter.  Moderate 
differences  of  temperature  produce  scarcely  any  perceptible  dif- 
ference in  the  tendency  which  the  blood  has  to  coagulate.  Within 
the  range  of  from  07°  to  105°,  blood  coagulates  in  the  same  time 
as  at  tlie  usual  temperature  of  98°,  Sir  Humphrey  Davy  found 
that  no  difference  in  this  respect  takes  place  when  blood  is  ex- 
posed to  nitrogen,  nitrous,  nitrous  oxide,  carbonic  acid,  carbo- 
nated hydrogen  gases,  or  atmospheric  air,  although  the  contrary- 
had  been  asserted.  Blood,  indeed,  coagulates  more  quickly  when 
placed  in  a  receiver  from  which  the  air  is  rapidly  exhausted, 
when  slowly  drawn  into  a  shallow  vessel,  or  when  exposed  to 
atmospheric  air,  at  a  temperature  of  120°.  This  process  is  re- 
tarded by  a  very  low  temperature.  Mr.  Hewson  placed  blood  in 
oil  at  a  temperature  of  38°;  at  the  expiration  of  six  hours  it  con- 
tinued fluid  ;  but  being  then  allowed  to  attain  a  warmer  tempera- 
ture, it  became  coagulated  in  twenty-five  minutes.  The  same 
physiologist  froze  a  portion  of  blood  confined  by  ligatures  in  the 
jugular  vein  of  a  rabbit ;  when  thawed,  the]  blood  became  liquified, 
and  coagulated.  Admixture  with  certain  neutral  salts  prevented 
altogether  coagulation  from  taking  place.  This  happened  when 
half  an  ounce  of  sulphate  of  soda  was  mixed  with  six  ounces  of 
fresh  blood  ;  but  on  the  addition  of  a  double  quantity  of  water 
coagulation  took  place.  Dr.  Turner  states  that  the  coagulation 
of  tile  blood  is  prevented  by  the  admixture  of  saturated  solutions 
of  chloride  of  sodium,  hydrochlorate  of  ammonia,  nitre,  and  potass ; 
while,  on  the  contrary,  alum  and  the  sulphates  of  the  oxides  of 
zinc  and  copper,  promote  coagulation.  Blood  coagulates  slowly 
when  drawn  quickly  into  a  deep  vessel,  or  when  detained  at  rest 
in  the  vein  of  a  living  animal  between  two  ligatures.  In  the  latter 
case,  Mr.  Hewson  found  the  blood  two-thirds  fluid  after  the  lapse 
of  three  hours  and  a  quarter.  When  the  experiment  was  varied 
by  blowing  air  into  the  vein,  the  blood  was  found  to  have  coag- 
ulated in  a  quarter  of  an  hour.  Blood  extravasated  through  the 
rupture  of  vessels,  and  retained  in  the  cavities  of  the  body,  often 
preserves  its  fluidity  for  a  very  considerable  time.  If  the  causes 
which  are  capable  of  postponing  coagulation  have  continued  to 
operate  beyond  a  certain  period,  the  blood  is  prevented  from  co- 
agulating ;  thus  recent  blood  remains  permanently  fluid  if  it  be 
constantly  stirred  for  some  minutes.  It  has  been  proved  by  the 
experiments  of  Hewson,  Hunter,  Deyeux,  and  Parmentier,  that 
the  coagulation  of  blood  is  not  entirely  prevented  by  diluting  it 
with  water;  but  Dr.  Crawford*  showed  that  this  process  is 
retarded  for  several  hours  by  the  admixture  of  blood  with  twelve 
times  its  bulk  of  water.f 

*  On  Animal  Heat,  p.  248. 

f  [From  recent  experiments,  made  by  Magendie  on  agents  that  are  capable 


17^ 


NUTRITIVE    FUNCTIONS. 


388.  There  are  many  conditions  of  the  living  system  that  have 
a  prodigious  influence  on  the  tendency  of  the  blood  to  coagulate, 
and  that  operate  in  a  manner  which  it  is  impossible  to  explain. 
Many  causes  of  sudden  death,  as  a  blow  upon  the  stomach,  or 
violent  injury  of  the  brain;  lightning  and  electricity;  several 
animal  poisons,  as  that  of  venomous  serpents ;  narcotic  vegetable 
principles,  as  cyanogen ;  also  excessive  exercise,  or  even  violent 
mental  emotions,  when  they  produce  the  sudden  extinction  of 
life,  prevent  the  usual  coagulation  of  the  blood  from  taking  place. 

389.  The  doctrine  maintained  by  Hunter,  that  the  blood  pos- 
sesses life,  and  that  its  coagulation  is  one  of  the  acts  of  this  living 
principle,  is  but  little  calculated  to  remove  the  difficulty ;  for  the 
operation  of  this  principle  in  producing  coagulation  would  be  as 
much  in  need  of  explanation  of  the  phenomenon  itself,  which  it 
professes  to  account  for.  We  must,  in  the  present  imperfect  state 
of  our  knowledge,  content  ourselves  with  referring  this  pheno- 
menon to  an  inherent  disposition  which  the  fibrin  possesses  to 
assume  the  solid  form,  when  no  counteracting  cause  is  present. 
Dr.  Bostock*  observes,  that  as  it  is  gradually  added  to  the  blood 
particle  by  particle,  whilst  this  fluid  is  in  a  state  of  agitation  in 
the  vessels,  it  has  no  opportunity  of  concreting ;  but  when  it  is 
suffered  to  lie  at  rest,  either  within  or  without  the  vessels,  it  is 
then  able  to  exercise  its  natural  tendency. 

390.  We  have  already  stated  that  the  crassamentum  consists 
chiefly  of  fibrin ;  but  it  owes  its  dark  colour  to  the  presence  of 
what  are  called  the  red  particles  of  the  blood,  and  which  are 
entangled  in  it  during  its  coagulation.     The  serum,  which  is  the 

'part  of  the  blood  that  remains  fluid  after  the  coagulation  of  the 
fibrin,  is  itself  coagulated  by  heat,  in  consequence  of  the  large 
proportion  of  albumen  it  contains ;  the  remaining  portion,  which 
still  continues  fluid,  is  termed  the  serosity.     The  following  is 

of  rendering  the  blood  liquid,  and  such  as  are  possessed  of  the  power  of  pro- 
moting its  coasulalion,  he  is  led  to  offer  the  followins  arrangement ;  observino-, 
at  the  same  time,  that  he  does  not  put  it  forward  as  final,  but  that,  on  the  con- 
trary, it  will  no  doubt  be  found  necessary,  from  improved  experience,  to  more  or 
less  modify  it. 

1.  Substances  ivhich  promote  the  coagulation  of  the  blood. — Water,  sugared 
water,  hydrochlorate  of  soda  ;  hydrochlorate  of  potassa  ;  hydrochlorate 
of  ammonia;  hydrochlorate  of  baryta  ;  serum  of  ascites  ;  boric  acid  ;  borax; 
nitrate  of  silver;  hydrosulphate  of  potass  and  ammonia;  Seltzer  water; 
Vichy  water;  Seidlitz  water;  ioduret  of  potassium;  tartrate  of  antimony 
and  potassa  ;  sulphate  of  magnesia  ;  alcohol;  cyanuret  of  gold  ;  cyanuret  of 
mercury  ;  acetate  andhydrochlorate  of  morphia,  and  mannite. 

2.  Substances  which  oppose  the  coagulation  of  the  hhod. — The  sulphuric,  hy- 
drochloric, nitric,  tartaric,  oxalic,  citric,  lactic,  acetic,  tannic,  and  hydrocy- 
anic acids  ;  soda,  potassa,  lime,  ammonia,  and  the  carbonates  of  soda,  potassa, 
and  ammonia.  Legons  sur  le  Sang,  &c.  and  the  translation  in  Lancet,  Jan.  20th, 
IS39.] 

*  Physiology,  p.  371. 


SANGUIFICATION.  179 

therefore  the  arrangement  of  the  principal  proximate  parts  of 
the  blood,  in  the  order  of  analysis. 

Coagulated  C  Crassamentum  |  ^e^^  particles. 

^^'?f    A         „  (Albumen. 

consists  of  (         Serum         |  Serosity: 

The  crassamentum  is  a  mass  of  soft  consistence,  which  easily 
bears  cutting  with  a  knife.  Its  mean  specific  gravity  is  about 
1-245.  By  long-continued  ablution  in  water,  it  may  be  freed 
from  the  red  particles  which  it  contains,  and  which  are  soluble 
in  water.  This  may  be  conveniently  effected  by  enclosing  the 
crassamentum  in  a  linen  bag,  immersing  it  repeatedly  in  water, 
and  at  the  same  time  pressing  it  gently  ;  or  by  allowing  a  stream 
of  water  to  fall  upon  it,  till  the  water  runs  off  colourless.  There 
remains  a  white,  solid  fibrous,  and  elastic  substance,  which  has 
all  the  properties  of  fibrin,  and  is  almost  exactly  similar  to  the 
basis  of  muscular  flesh  obtained  b}'  long  boiling.  It  may  also  be 
procured  directly  from  recent  blood,  by  stirring  it,  as  it  flows 
from  the  vessel,  with  a  bunch  of  twigs  ;  or  receiving  it  into  a 
bottle,  and  shaking  it  during  its  coagulation.  When  formed  under 
these  circumstances,  it  exhibits  a  fibrous  appearance,  and  the 
whole  is  converted  into  an  irregular  net-work  of  dense  fibres. 
Fibrin  was  formerly  known  under  the  name  of  coagulable  lymphs 
or  gluten. 

392.  The  red  particles  or  globules,  contained  in  the  blood,  and  en- 
veloped in  the  fibrin  during  its  coagulation,  have  long  attracted  the 
attention  of  physiologists,  from  the  irregularity  of  their  appearance, 
and  the  importance  which  was  supposed  to  attach  to  them.  The 
first  notice  which  we  find  of  them  occurs  in  the  writings  of  Mal- 
pighi,  soon  after  the  introduction  of  the  use  of  the  microscope. 
They  were  soon  afterwards  examined  with  great  care  and  mi- 
nuteness by  the  indefatigable  Leewenhoek,  whose  name  stands 
foremost  among  those  who  made  observations  with  this  instrument. 
They  soon  became  the  subject  of  much  speculation,  and  laid  the 
foundation  of  many  fanciful  hypotheses  which  were  current  at 
the  time,  but  are  now  consigned  to  deserve  neglect.  Leewen- 
hoek him.self  was  led  by  his  imagination  to  the  belief  that  these 
red  globules  were  each  composed  of  a  series  of  globular  bodies 
of  different  orders  descending  in  regular  gradations.  He  supposed 
eachtobemadeupof  six  particles  of  serum;  each  particle  of  serum 
of  six  particles  of  lymph,  and  so  on  in  succession.  This  strange 
hypothesis,  visionary  as  it  now  appears,  was  so  accordant  with  the 
prevailing  taste  for  mathematical  disquisitions,  that  it  was  very 
generally  adopted,  and  held  a  powerful  sway  over  the  opinions  and 
reasonings  of  the  physicians  of  that  age.    It  forms  a  leading  feature 


180  NUTRITIVE    FUNCTIONS. 

in  the  pathological  speculations  of  Boerhaave ;  and  although  its 
futihty  was  sufficiently  exposed  by  Lancisi  and  Senac,  it  main- 
tained its  ground  even  to  the  time  of  Haller. 

393.  But  a  better  spirit  began  at  length  to  prevail ;  the  illusive 
dreams  of  fancy  were  superseded  by  the  sober  and  attentive  obser- 
vation of  nature  ;  and  truth  was  sought  by  the  judicious  cultiva- 
tion of  experimental  inquiry,  the  only  legitimate  path  by  which 
it  can  be  approached.  About  the  middle  of  the  eighteenth  century, 
the  Abbe  de  la  Torre,  employing  microscopes  of  considerable 
power,  obtained  the  appearance  of  flattened  annular  bodies, 
with  a  perforation  in  the  centre.  Hewson,  who  observed  them 
with  still  greater  attention  to  accuracy,  states  them  to  be 
hollow  vesicles  of  a  flattened  shape,  and  containing  a  smaller, 
solid,  and  spherical  particle,  which  was  freely  moveable  within 
them,  or,  as  he  compares  it,  "likea.  pea  in  a  bladder."  He  as- 
serted, that  by  adding  water,  these  particles  swell  out  into  a 
globular  shape,  and  afterwards  burst  and  disappear,  in  conse- 
quence of  their  being  dissolved  in  the  water ;  but  if  moistened 
with  an  aqueous  solution  of  any  neutral  salt,  they  preserve  their 
natural  flat  shape,  Cavallo  describes  them  as  much  more  irre- 
gular in  their  form  than  Hewson  represented  them  ;  and  he  was 
led  from  his  observations  to  the  conclusion  that  the  appearance 
either  of  a  perforation,  or  of  a  central  particle,  is  in  reality  an 
optical  deception,  arising  from  the  refraction  of  the  light  by  which 
the  objects  are  viewed,  as  it  passes  through  the  convex  surfaces 
of  the  globules.  He  also  endeavours  to  explain  the  appearance 
which  led  Hewson  to  believe  that  the  central  nucleus  is  moveable 
within  the  external  vesicle,  by  some  apparent  change  in  the 
position  of  the  luminous  image,  in  consequence  of  accidental 
variations  in  the  direction  in  which  the  light  is  viewed.  Very 
small  artificial  globules  of  solid  glass  which  he  constructed  for 
the  purpose,  presented  under  the  microscope  very  nearly  the  same 
appearances,  as  the  globules  of  the  blood ;  and  hence  he  con- 
cluded, that  the  latter,  notwithstanding  these  appearances,  were 
nearly  globular  and  composed  of  a  uniform  material. 

394.  Notwithstanding  the  ingenuity  displayed  in  this  reasoning, 
the  more  profound  examination  which  the  subject  has  received 
from  Dr.  Young,  induces  us  to  revert,  to  a  certain  extent,  to  the 
opinion  of  Hewson.  He  observes  that  in  such  examinations  it 
is  only  necessary  to  employ  a  full  and  unlimited  light,  in  order  to 
obtain  a  very  distinct  outline  of  what  appears  manifestly  to  be  a 
very  simple  substance.  But  we  should  remember  that  where 
the  substances  to  be  examined  are  perfectly  transparent,  it  is  only 
in  a  confined  and  diversified  light  that  we  can  gain  a  correct 
idea  of  their  structure.  The  eye  is  best  prepared  for  the  inves- 
tigation by  beginning  with  the  blood  of  a  skate,  ,of  which  the 
particles  are,  from  their  greater  size,  so  conspicuous,  and  of  so 


SANGUIFICATION.  181 

unequivocal  a  form,  as  at  once  to  set  aside  the  idea  of  a  simple 
homogeneous  substance.  They  are  oval  and  depressed,  like  an 
almond,  but  less  pointed,  and  a  little  flatter.  Each  of  them 
contains  a  round  nucleus  which  is  wholly  independent  in  its 
appearance  of  the  figure  of  the  whole  disc,  being  sometimes  a 
little  irregular  in  its  form,  seldom  deviating  from  its  central  situa- 
tion, but  often  remaining  distinctly  visible,  whilst  the  oval  partis 
scarcely  perceptible.  This  nucleus  is  about  the  size  of  a  particle 
of  human  blood,  the  whole  oval  being  about  twice  as  wide,  and 
not  quite  three  times  as  long.  The  nucleus  is  very  transparent, 
and  forms  a  distinct  image  of  any  large  object  which  intercepts 
a  part  of  the  light  by  which  it  is  seen,  but  exhibits  no  inequalities 
of  light  and  shade  that  could  lead  to  any  mistake  respecting  its 
form.  But  if  we  place  some  particles  of  human  blood  under 
similar  circumstances,  near  the  confines  of  light  and  shade, 
although  they  are  little,  if  at  all  less  transparent,  we  immediately 
see  an  annular  shade  on  the  disc,  which  is  most  marked  on  the 
side  of  the  centre  on  which  the  marginal  part  appears  the  brightest, 
and  consequently  indicates  a  depression  in  the  centre,  which  De 
la  Torre  mistook  for  a  perforation.  It  is  most  observable  when 
the  drop  is  dying  away,  so  that  the  particles  rest  on  the  glass ; 
and  when  a  smaller  particle  is  viewed,  it  has  merely  a  dark  cen- 
tral spot,  without  any  lighter  central  space.  Dr.  Monro  had 
represented  the  globules  of  the  blood  as  being  of  an  exceedingly 
flattened  shape,  or,  as  he  expresses  it,  "  as  flat  as  a  guinea." 
But  Dr.  Young  never  saw  them  of  this  shape,  although  he  states 
their  axis  as  being  sometimes  not  more  than  one-third,  or  one- 
fourth  of  their  greatest  diameter.  He  also  states  that  they  do 
not  seem,  as  Hewson  asserted,  to  have  their  dimensions  much 
affected  by  the  fluid  in  which  they  are  suspended,  since  they  may 
easily  be  spread  thin  on  glass,  and  dried  without  much  change 
in  their  magnitude,  at  least  in  the  direction  of  the  surface  to 
which  they  adhere  ;  and  they  remain  distinct  as  long  as  the  access 
of  moist  air  is  completely  excluded.  When  they  have  been  kept 
for  some  time  in  water,  and  a  little  solution  of  salt  is  added,  their 
form  and  structure,  as  Hewson  observed,  are  more  easily  ex- 
amined, and  appear  to  resemble  those  of  a  soft  substance,  with 
a  denser  nucleus ;  but  the  comparison  which  he  makes  of  their 
being  like  a  pea  in  a  bladder,  Dr.  Young  thinks  is  quite  inappli- 
cable. 

395.  It  has  commonly  been  asserted,  and  especially  by  Hew- 
son, that  these  particles  are  readily  soluble  in  water ;  but  Dr. 
Young  has  shown  that  this  opinion  is  erroneous,  and  depends 
partly  on  their  passing  readily  through  the  filtering  paper,  a  cir- 
cumstance observed  by  BerzeUus,  and  partly  on  the  extraction  of 
a  great  part  of  their  colouring  matter,  together  with  which  they 
lose  much  of  their  specific  gravity,  so  that  instead  of  subsiding, 

16 


182  NUTRITIVE    FUNCTIONS. 

they  are  generally  suspended  in  the  fluid.  Their  presence  may 
still,  however,  be  detected  by  a  careful  examination ;  and  they 
seem  in  this  state  to  have  recovered  in  some  measure  their  origi- 
nal form,  which  they  had  lost  when  first  immersed  in  the  water. 
A  curious  observation  on  the  influence  of  circumstances  on  the 
form  of  the  globules,  has  been  made  by  Mr.  Bauer.  He  remarks 
that  in  the  skate  they  are  oval  during  the  life  of  the  animal,  but 
become  flattened  after  its  death.  This  circumstance  may  per- 
haps tend  to  reconcile  some  of  the  discordant  statements  which 
have  been  made  on  this  subject. 

396.  The  size  of  the  red  globules  has  also  been  very  differently 
estimated  by  different  observers.  These  discrepancies  receive 
some  explanation  by  the  circumstance  which  Dr.  Milne  Edwards 
appears  to  have  established,  of  the  globules  dilfering  considerably 
in  their  size  in  the  same  individual.*  The  most  accurate  mea- 
surements appear  to  be  those  of  Dr.  Young,  and  of  Captain 
Kater,  who  both  agree  that  the  particles  of  human  blood  are 
between  the  four-thousandth  and  the  six-thousandth  of  an  inch  in 
their  diameter;  and  they  may  therefore  be  taken  at  a  medium 
at  the  five-thousandth  of  an  inch.  Mr.  Bauer  has  stated  them 
to  be  considerably  larger,  even  as  much  as  the  one  thousand- 
seven-hundredth  of  an  inch  in  their  entire  state,  and  that  the  cen- 
tral part  is  the  two-thousandth  of  an  inch  in  diameter.  But  the 
observations  of  Dr.  Young  are  more  probably  correct,  from  their 
coincidence  with  those  of  Captain  Kater,  which  were  conducted 
in  a  dififerent  manner.  <■ 

397.  The  diificulty  of  procuring  the  red  particles  in  a  separate 
state,  unmixed  with  serum,  is  so  great  as  to  preclude  us  from  ob- 
taining any  distinct  knowledge  of  their  chemical  composition  and 
properties.  The  colouring  matter  of  the  blood  has  been  termed 
hematine,  or  hematosine.  But  according  to  M.  Lecanu,  the  sub- 
stance usually  termed  hematine  is  in  reality  a  combination  of 
albumen  and  the  pure  colouring  matter  of  the  blood,  which  he 
proposes  to  designate  glohuline.  Although  it  appears  from  Dr. 
Young's  observations,  that  the  globules  themselves  do  not  dis- 
solve in  water,  yet  they  impart  to  it  the  whole  of  their  colouring 
matter.  The  watery  solution  turns  syrup  of  violets  green;  and 
after  some  time  deposits  a  flocculent  precipitate,  probably  from 
the  coagulation  of  albumen,  the  presence  of  which  is  indicated 
also  by  the  effect  of  boiling  the  solution.  Hence  it  has  been  con- 
cluded that  the  colouring  matter  consists  of  albumen,  dissolved 
by  an  excess  of  pure  soda.  When  evaporated  and  calcined  in  a 
crucible,  a  residuum  is  obtained,  amounting  to  about  one-thou- 
sandth of  the  weight  of  solid  matter,  and  composed,  according  to 
Pourcroy  and  Vauquelin,  chiefly  of  subphosphate  of  iron. 

*  Cyclopasdia  of  Anat.  art.  Blood. 


SANGUIFICATION.  183 

398.  Berzelius,*  who  has  made  minute  inquiry  into  this  subject, 
informs  us  that  the  colouring  matter  of  the  ijlood,  separated  from 
tile  other  part,  leaves  one-eightieth  of  an  incombustible  residuum, 
of  which  rather  more  than  one-half  is  an  oxide  of  iron.  The  ex- 
istence of  iron  in  the  blood  was  first  discovered  by  Menghini ; 
but  its  amount  was  much  over-rated  both  by  himself  and  many 
of  the  earlier  chemists  who  succeeded  him.  It  is  difficult  to 
determine  in  what  state  this  iron  exists  in  the  blood.  It  would 
appear  not  to  be  in  the  state  of  any  of  the  known  salts  of  this 
metal ;  because  before  the  blood  has  been  calcined,  the  iron 
escapes  detection  by  any  of  the  tests  which  usually  indicate  its 
presence  in  solutions  ;  and  yet  the  solubility  of  the  colouring 
matter  in  the  serum  would,  on  the  other  hand,  appear  to  support 
the  opinion  of  its  possessing  saline  properties.  Berzelius  has  been 
able  to  deduce  from  his  numerous  experiments  on  this  point, 
merely  the  negative  conclusion,  that  no  salt  of  iron  which  he 
tried  was  capable  of  being  combined  with  the  serum,  so  as  to 
produce  a  compound  similar  to  the  colouring  matter  of  the 
blood;  thus  refuting  the  alleged  synthetic  proof  adduced  by 
Fourcroy,  who  had  stated  that  subphosphate  of  iron  dissolves  in 
albumen,  and  imparts  to  it  a  bright  red  colour,  resen)bling  that 
of  blood.t 

399.  It  has  long  been  the  prevailing  opinion  that  the  blood 
derives  its  red  colour  from  the  iron  it  contains ;  but  the  truth  of 
this  opinion  has  been  called  in  question  by  many  writers  of  high 
authority,  and  in  particular  by  Dr.  WellsJ  and  by  Mr.  Brande.§ 
The  experiments  of  Dr.  Wells,  however,  as  is  remarked  by  Dr. 
Bostock,  seem  only  to  prove  that  the  colour  of  the  blood  is  not 
occasioned  by  any  salt  of  iron,  or  by  iron  in  such  a  state  as  to 
be  affected  by  the  ordinary  tests.  Mr.  Brande  procured  the 
colouring  matter  from  venous  blood  in  a  detached  state,  by  re- 
moving the  fibrin  from  it  by  agitation  while  it  was  coagulating, 
and  suffering  the  red  globules  to  subside  in  tlie  serum,  from  which 
they  could  be  obtained  in  a  concentrated  form.  Examining  this 
portion  by  means  of  different  reagents,  he  arrived  at  the  conclu- 
sion, that  the  colouring  principle  of  the  blood  is  an  animal  sub- 
stance of  a  peculiar  nature,  susceptible,  like  the  colouring  matter 
from  vegetables,  of  uniting  with  bases,  or  mordants,  and  there- 
fore admitting  of  being  applied  in  the  art  of  dyeing.  The  most 
effectual  mordants  for  the  colouring  matter  of  the  blood  are  the 
salts  of  mercury,  especially  the  nitrate,  and  the  bichloride  or 
corrosive  sublimate.  On  examining  the  colouring  matter  distinct 
from  the  crassamentum,  Mr.  Brande  did  not  discover  a  greater 
proportion  of  iron  than  exists  in  the  other  principles  of  blood. 

*  Medico-Chirurgical  Transactions,  vol.  iii.  p.  215. 

f  Systeme  de  Connais,  Chymiques,  vol.  ix.  p.  207,  208. 

X  Phil.  Trans,  for  1797,  p.  410.  §  Phil.  Trans,  for  1812,  p.  90. 


184  NUTRITIVE    FUNCTIONS. 

These  results,  in  as  far  as  they  relate  to  the  quantity  of  iron,  are 
at  variance  with  the  later  and  apparently  more  elaborate  experi- 
ments of  Berzelius,  who  still  maintains  that  the  colouring  matter 
of  the  blood  contains  iron,  not  indeed  discoverable  by  reagents, 
but  decisively  proved  to  exist  in  its  ashes.  In  every  respect, 
except  in  containing  that  metal,  the  colouring  matter  agrees  with 
fibrin  and  albumen ;  and  he  seems  disposed  to  believe  that  its 
colour,  though  not  depending  on  the  presence  merely  of  an  oxide 
of  iron,  may  be  produced  by  a  compound  of  which  the  oxide  is 
an  essential  part.    ^ 

Vauquelin's  experiments*  may  in  some  respects  be  deemed  to 
corroborate  those  of  Brande,  inasmuch  as  they  show  that  iron 
cannot  be  detected  by  liquid  tests  in  solutions  of  the  colouring 
matter;  but  they  at  the  same  time  show  that  this  metal  is  readily 
detected  by  these  tests  in  the  fluid  from  which  the  colouring 
matter  has  subsided. 

400.  The  changes  in  the  colour  of  the  blood  produced  by  its 
exposure  to  different  gases,  are  probably  owing  to  their  action  on 
the  red  globules.  Arterial  blood  is  blackened,  and  venous  blood 
rendered  darker,  by  nitrogen,  or  carbonic  acid  gases ;  but  its 
bright  florid  hue  is  restored  by  exposure  to  oxygen  gas.  We 
shall  have  occasion  to  revert  to  this  subject  in  treating  of  respi- 
ration. 

401.  Besides  the  ordinary  red  globules,  others  of  a  much 
smaller  size  have  been  detected  by  Mr.  Bauer  floating  in  the 
serum,  and  even  apparently  generated  while  the  fluid  is  under 
examination.  To  these  Sir  Everard  Home  gave  the  name  of 
lymph  globules.i 

402.  The  serum  of  the  blood,  or  the  fluid  part  which  is  left 
after  the  separation  of  the  crassamentum,  is  a  transparent  and 
apparently  homogeneous  liquid,  of  a  yellowish  and  sometimes 
greenish  colour,  of  a  saline  taste  and  adhesive  consistence.  Its 
specific  gravity  is  variable,  but  may  be  taken,  on  an  average,  at  . 
about  1-025.J  When  exposed  to  a  temperature  of  160°,  the 
whole  is  converted  into  a  firm  white  mass,  perfectly  analogous 
to  the  white  of  an  egg  which  has  been  hardened  by  boiling.  It 
may,  in  fact,  be  regarded  as  identical  with  coagulated  albumen, 
the  chemical  properties  of  which  we  have  already  described. 

403.  Although  the  whole  of  the  mass  of  serum  appears  to  be 
rendered  solid  by  the  process  of  coagulation,  yet  if  this  coagu- 
lum  be  cut  into  slices,  and  subjected  to  gentle  pressure,  or  if  it 
be  placed  on  the  mouth  of  a  funnel,  a  small  quantity  of  a  slightly 

*  Annales  de  Chiniie  et  de  Physique,  i.  9. 

t  Phil.  Trans,  for  1819,  p.  2. 

if.  [This  may  be  near  the  average,  but  the  specific  gravity  differs  greatly. 
Thackrah,  (^Inquiry  into  the  Nature  and  Properties  of  the  Blood,  &c.,  Lond 
1819,)  found  the  extremes  to  be  1.004  and  1.080.] 


SANGUIFICATION.  185 

opaque  liquor  drains  from  it,  whicii  is  called  the  serosity.  It  has 
a  saline  taste,  and  a  peculiar  odour,  and  consists  of  several  ingre- 
dients. Its  existence  as  a  substance  distinct  from  the  albumen 
was  first  pointed  out  by  Dr.  Butt  in  1760,  and  its  properties  were 
further  examined  by  Dr.  Cullen,  who  speaks  of  it  as  a  solution  of 
fibrin  in  water.  Hewson  believed  it  to  be  of  a  mucous  nature. 
Parmentier  and  Deyeux  published,  in  1790,  an  elaborate  set  of 
experiments  which  they  made  upon  it,  from  which  they  drew  the 
conclusion,  that  the  animal  substance  contained  in  the  serosity 
was  gelatin.  This  statement  seemed  so  satisfactory,  from  the 
apparent  accuracy  of  the  investigation,  that  it  was  generally 
acquiesced  in.  Not  only  was  jelly  considered  as  one  of  the  con- 
stituents of  the  blood,  but  means  were  pointed  out  for  ascertain- 
ing its  proportion  ;  and  its  supposed  agency  in  the  economy  was 
made  the  foundation  of  many  physiological  speculations.  But 
Dr.  Bostock  has  since  proved  that  this  opinion  is  not  founded  in 
fact.  He  was  unable  to  detect  the  smallest  quantity  of  jelly 
either  in  the  serosity  of  the  blood,  or  in  any  other  of  the  albumi- 
nous fluids.  In  this  conclusion  he  is  fully  supported  by  the  testi- 
monies of  Berzelius,  Marcet,  and  Brande. 

404.  It  may  be  inferred  from  the  experiments  of  Mr.  Brande, 
that  serosity  consists  of  a  small  quantity  of  albumen,  still  retained 
in  solution  by  a  large  proportion  of  alkali.  According  to  Berze- 
lius, the  serosity  contains  no  sulphuric  acid,  and  only  a  vestige  of 
the  phosphoric,  and  consists  chiefly  of  water,  with  some  pure 
soda  holding  albumen  in  solution,  of  muriates  of  soda  and  potass, 
of  lactate  of  soda,  and  a  peculiar  animal  matter  which  always 
accompanies  the  lactate.  Dr.  Bostock  found  the  amount  of  solid 
contents  to  vary  from  the  forty-sixth  to  the  seventieth  part  of  its 
weight,  or,  on  an  average,  about  the  fiftieth.  It  has  been  a 
matter  of  dispute  which  of  the  mineral  alkalies  exists  in  serum  in 
an  uncombined  form.  Dr.  Pearson  maintained  that  it  was  potass; 
but  Drs.  Bostock,  Marcet,  and  Berzelius,  with  much  greater 
appearance  of  correctness,  allege  that  it  is  soda. 

405.  The  component  parts  of  human  serum,  according  to  the 
analysis  of  Dr.  Marcet,  are — 

Water,       -         -         -         - 

Albumen, 

Muriates  of  potass  and  soda, 
Muco-extractive  matter,      ... 
Subcarbonate  of  soda, 
Sulphate  of  potass,  ... 

Earthy  phosphates,  .         .         - 

1000- 

406.  This  analysis  coincides  verv  nearly  with  that  of  Berzelius, 

16* 


900- 

86-8 

6-6 

4- 

1-95 

•35 

•6 

186 


NUTRITIVE    rUNCTIONS. 


who  considers  the  substance  ternned  by  Dr.  Marcet  muco-exirac- 
tive  matter  to  be  impure  lactate  of  soda.  But  Dr.  Bostock  is  led 
by  his  experiments  to  the  conclusion,  that  a  peculiar  animal  sub- 
stance exists  in  the  serosity,  not  coagulable  by  heat,  or  by  any 
other  means ;  not  affected  by  corrosive  sublimate,  or  by  tannin, 
which  are  the  appropriate  tests  of  albumen  and  of  jelly  respec- 
tively, but  copiously  precipitated  by  muriate  of  tin,  and  still  more 
readily  by  the  acetate  of  lead ;  and  he  thinks  this  substance  is 
quite  independent  of  the  lactate  of  soda,  which  may  exist  at  the 
same  time  in  the  blood. 

407.  Wienholt  discovered  that  the  serosity  contained  a  small 
quantity  of  the  peculiar  substance  which  exists  in  greatest  abun- 
dance in  the  flesh  of  animals,  and  was  first  noticed  as  a  distinct 
proximate  principle  by  Rouelle.  It  was  subsequently  termed 
ozmazome  by  Thenard,  who  examined  its  properties  more  minute- 
ly. This  substance  is  of  a  yellowish  brown  colour ;  it  is  soluble 
both  in  water  and  in  alcohol,  and  is  precipitated  by  infusion  of 
nutgalls,  nitrate  of  mercury,  and  by  the  acetate  and  nitrate  of 
lead.  It  is  still  a  matter  of  uncertainty  what  connexion  exists 
between  this  substance  and  the  muco-extractive  matter  above 
mentioned.  There  is  also  another  proximate  principle,  namely, 
urea,  of  which  we  shall  afterwards  have  occasion  to  speak,  which 
is  found  in  small  quantity  in  the  blood,  when  that  fluid  is  in  its 
natural  state,  but  which  is  abundantly  found  in  the  blood  of  ani- 
mals from  which  the  kidneys  have  been  removed.  Besides  these, 
Dr.  B.  Babington  discovered  the  presence  in  the  blood  of  an  oily 
substance,  separable  from  the  other  parts  by  means  of  ether. 
Lecanu,  in  addition  to  this  oily  matter,  found  a  crystallizable 
fatty  matter  in  the  blood  ;  and  similar  observations  have  been 
made  by  Chevreul.  Manganese  is  said  to  have  been  detected  in 
the  blood  by  Wurzer.  M.  Boudet  has  also  lately  discovered  a 
new  substance  in  the  serum,  which  he  has  termed  iiroline.  This 
is  a  white,  slightly  opalescent  substance,  fusible  at  94°  Fahren- 
heit, not  forming  an  emulsion  with  water,  soluble  in  alcohol,  not 
saponifiable,  and  apparently  containing  nitrogen.* 

*  [Dr.  B.  Babington  is  of  opinion,  that  the  blood,  whilst  circulating  in  the 
vessels  consists  of  two  parts  only — a  fluid  which  he  calls  liquor  sanguinis, 
and  red  globules ;  and  he  is  induced  to  believe,  from  his  experiments,  that 
fibrin  and  serum  do  not  exist  as  such  in  the  circulating  fluid,  but  that  the 
liquor  sanguinis,  when  removed  from  the  vessels,  and  no  longer  subjected 
to  the  laws  of  life,  has  then,  and  not  before,  the  property  of  separating  into 
fibrin  and  serum.  Med.  Chirurg.  Transact,  vol.  xvi.  pt.  2.  Lond.  1831,  and 
art.  Blood  (morbid  conditions  of  the),  in  Cyclop,  of  Anat.  and  Physiol.  Lond. 
1836.1 


CIRCULATION    OF    THE    BLOOD.  187 

CHAPTER  VIIL 

CIRCULATION.  * 

Sect.  I. — Apparatus  fm-  Circulation. 

408.  The  object  of  the  function  of  circulation  is  twofold. 
The  first  is  to  distribute  to  all  the  organs  that  due  share  of  nutri- 
tive fluid  which  they  require  for  the  performance  of  their  respec- 
tive offices,  for  the  maintenance  of  their  temperature,  and  for 
nutrition,  and  to  keep  up  a  constant  supply  of  this  fluid.  The 
second,  and  no  less  important  object,  is  to  expose  every  portion 
in  succession  of  this  fluid,  which  is  the  blood,  to  the  influence  of 
atmospheric  air  in  an  organ  appropriated  to  this  particular  pur- 
pose ;  the  continual  renewal  of  the  action  of  the  oxygen,  contained 
in  the  air  upon  the  blood,  being  necessary  for  the  maintenance  of 
its  salutary  qualities,  and  indispensable  to  the  preservation  of  life. 
The  organs  in  which  this  process  is  carried  on  are  the  lungs; 
and  the  function  by  which  it  is  accomplished  is  respiration.  The 
great  agent  for  the  distribution  of  the  blood  both  generally  to 
the  organs  of  the  body,  and  specially  to  the  lungs,  is  the  heart ; 
the  pipes  through  which  it  is  conveyed  to  those  parts  are  the 
arteries ;  those  through  which  it  is  brought  back  to  the  heart,  the 
veins.  A  set  of  finer  vessels  interposed  between  the  minute  ex- 
tremities of  the  arteries,  and  the  minute  beginnings  of  the  veins, 
are  called  the  capillaries.  The  structure  and  distribution  of  all 
these  parts  belongs  to  Anatomy.  The  following  brief  capitulation, 
however,  of  the  structure  of  the  heart,  will  assist  us  in  understand- 
ing the  physiology  of  its  action. 

1.  Cardiac  Apparatus. 

409,  The  heart  is  a  hollow  muscle,  of  a  conical  shape,  occupy- 
ing the  central  and  inferior  part  of  the  cavity  of  the  thorax,  hav- 
ing its  basis  turned  towards  the  right  side,  and  its  point  or  apex 
towards  the  left,  nearly  opposite  to  the  space  between  the  sixth 
and  seventh  ribs.  Its  lower  surface  is  somewhat  flattened,  where 
it  lies  upon  the  diaphragm.  Its  basis,  with  which  the  great  ves- 
sels are  connected,  is  covered  with  fat.  The  whole  heart,  and 
the  roots  of  the  large  blood-vessels  at  its  basis,  are  protected  by 
a  general  investment  of  membrane,  which  is  a  reflected  produc- 
tion of  an  extended  serous  membrane,  forming  a  cavity  for  its 
reception,  and  for  allowing  it  considerable  freedom  of  motion. 
This  membrane,  which  is  remarkable  for  its  strength,  is  called 


188  NUTRITIVE    FUNCTIONS. 

the  pericardium,  and  is  situate  between  the  laminae  of  the  medias- 
tinum, which  are  separated  in  order  to  contain  it. 

410.  The  heart  is  principally  made  up  of  muscular  fibres,  the 
course  of  which  is  extremely  complex ;  some  extending  longi- 
tudinally from  the  basis  to  the  apex,  others  taking  an  oblique  or 
spiral  course ;  and  a  third  running  in  a  more  transverse  direc- 
tion. There  are  two  considerable  cavities,  called  ventricles,  dis- 
tinguished, according  to  their  situation,  into  the  right  and  left. 
The  former  has  also  been  called,  in  reference  to  its  functions,  the 
pulmonic,  and  the  latter  the  systemic  ventricle.  They  are  sepa- 
rated by  a  strong  and  thick  partition,  called  the  septum  ventricu- 
lorum,  which  is  composed  of  fleshy  and  tendinous  fibres.  At- 
tached to  these,  at  the  basis  of  the  heart,  are  two  hollow  and 
fleshy  projecting  appendages,  called  the  auricles,  the  cavities  of 
which  are  also  separated  from  each  other  by  a  partition,  distin- 
guished by  the  name  of  septum  auriculorum,  and  they  open  into 
those  of  the  ventricles.  The  right  auricle,  which,  together  with 
the  right  ventricle,  is  placed  more  in  front,  receives  the  blood 
from  the  venee  cavae,  and  transmits  it  to  the  right  ventricle,  by 
which  it  is  propelled  into  the  trunk  of  the  pulmonary  artery. 
The  left  auricle,  in  like  manner,  collects  the  blood  from  the  four 
trunks  of  the  pulmonary  veins,  and  transfers  it  into  the  left  ven- 
tricle, by  which  it  is  forcibly  driven  into  the  aorta,  or  main  trunk 
of  the  arterial  system  of  the  body  at  large.  The  membrane 
which  lines  the  cavities  of  the  heart,  and  the  great  vessels  just 
mentioned,  is  produced  so  as  to  form  valves  at  the  two  orifices 
of  both  the  ventricles;  that  is,  where  the  auricles  open  into  them, 
and  also  at  the  origin  of  the  arterial  trunks  which  arise  from  the 
ventricles.  The  valves  placed  between  the  right  auricle  and  ven- 
tricle, are  usually  three  in  number,  and  are  called,  valvulcB  tricus- 
pides;  but  in  the  left  ventricle  there  are  only  two,  and  these  are 
namecl  the  valvulcB  mitrales.  The  membranes  which  form  these 
valves  are  attached  so  as  to  project  somewhat  forward  in  each 
of  these  cavities,  and  are  connected  with  tendinous  strings,  called 
chordcB  tendinecB,  which  arise  from  detached  and  projecting  por- 
tions of  the  muscular  substance  of  the  heart,  named  from  their 
cylindrical  form,  carnea  columncB. 

411.  The  valves  at  the  origin  both  of  the  pulmonary  artery 
and  of  the  aorta,  are  three  in  number,  and  are  called  the  vahulce 
semilunares,  from  their  semicircular  figure ;  their  convexities  are 
turned  towards  the  ventricle ;  they  are  concave  next  to  the  cavity 
of  the  artery ;  and  in  the  middle  of  their  loose  edge  is  found  a 
small  hard  triangular  substance  called  corpus  Arantii,  and  some- 
times corpusculum  Morgagni,  or  sesamoideum.  When  these  valves 
are  made  to  approach  each  other,  by  the  pressure  of  the  blood 
in  the  artery  in  the  direction  of  the  ventricle,  they  unite  so  as 
completely  to  close  the  passage,  and  prevent  any  of  the  blood 


CIRCULATION    OF    THE    BLOOD.  189 

from  returning.  Opposite  to  tlie  semilunar  valves,  the  artery 
bulges  out  and  forms  three  projections,  which  have  correspond- 
ing pits  or  depressions  within,  and  are  called,  from  their  dis- 
coverer, si7ius  VahalvcB. 

412.  Where  the  two  venai  cavae  meet,  there  is  a  small  angular 
projection,  which  has  been  called  the  tuberculum  Loweri.  The 
term  auricula  more  properly  applies  to  the  jagged  portions  which 
project  from  the  sides  of  the  base  of  the  heart,  like  the  ears  of  a 
dog  from  its  head ;  whilst  the  expanded  cavity  where  the  venous 
tubes  enter  is  called  the  sinus  venosus.  On  the  side  next  to  the 
auricula,  there  is  a  remarkable  semilunar  fold,  projecting  within 
the  cavity,  between  the  vein  and  auricle,  so  as  to  be  convex  next 
to  the  vein,  and  concave  next  to  the  auricle.  This  doubling  has 
been  called  the  Eustachian  valve.  Between  the  concave  part  of 
this  fold,  and  the  opening  into  the  ventricle,  is  the  orifice  of  the 
coronary  vein,  which  returns  the  blood  that  has  circulated 
through  the  substance  of  the  heart  itself,  and  which  is  provided, 
at  this  point,  with  its  proper  valve.  In  the  septum  auriculum  is 
seen  a  depression,  the  fossa  avails,  which  is  the  remains  of  a  pas- 
sage of  communication  between  the  right  and  left  auricles  that 
had  existed  in  the  foetal  state.  The  sides  of  the  fossa  ovalis  are 
strong  and  thick,  and  have  received  the  name  of  isthmus  Vicus- 
senii,  or  columnce,  or  annulus  fosscE  ovalis. 

2.  Sanguiferous  System  in  general. 

413.  The  blood-vessels,  consisting  of  arteries,  veins,  and  capil- 
laries, compose  by  their  assemblage  what  is  termed  the  sangui- 
ferous system  ;  and  the  channels  which  they  form  for  the  trans- 
mission of  the  blood  constitute  a  double  circuit.  The  principal 
circuit  consists  of  that  through  which  the  blood  is  distributed  to 
all  parts  of  the  body  indiscriminately,  and  which  includes  there- 
fore the  whole  system.  But  there  is  also  another  circuit  of  lesser 
extent,  which  is  performed  by  the  blood,  by  its  being  sent  from 
the  heart  to  the  lungs,  and  again  returned  to  the  heart,  after  cir- 
culating through  those  organs.  This  is  termed  the  lesser  circu- 
lation, by  way  of  contrast  with  the  circulation  through  all  the  rest 
of  the  body,  which  constitutes  the  greater  circulation.  For 
effecting  this  lesser  circulation,  a  distinct  set  of  blood-vessels, 
namely,  the  -pulmonary  vessels,  is  provided. 

414.  Thus,  there  are  two  separate  systems  of  blood-vessels, 
which  have  no  communication  with  each  other,  except  through 
the  medium  of  the  heart,  which  is  the  common  origin  and  termi- 
nation of  both.  The  aortic  system,  or,  as  some  modern  anatomists 
have  chosen  to  designate  it,  the  systemic  system,  is  that  which, 
taking  its  rise  from  the  left  ventricle  of  the  heart,  begins  with  the 
aorta,  or  main  trunk  of  the  arties  which  transmit  the  blood  to  the 


190  NUTRITIVE    FUNCTIONS. 

body  at  large,  and  is  completed  by  the  veins  which  are  collected 
into  two  trunks,  called  vencB  cavce;  which  trunks,  again,  terminate 
in  the  right  auricle  of  the  heart.  The  pulmonary  system,  on  the 
other  hand,  comprises  the  pulmonary  arteries,  which  arise  by  a 
single  trunk  from  the  right  ventricle  of  the  heart,  and  after  cir- 
culating the  blood  through  the  lungs,  are  continued  into  the  pul- 
monary veins,  and  terminate  by  four  large  trunks  in  the  left 
auricle  of  the  heart. 

415.  All  these  vessels,  whether  arteries  or  veins,  may  be  com- 
prehended under  the  following  general  description.  They  are 
flexible  and  elastic  tubes,  for  the  most  part  of  a  cylindrical  shape, 
and  composed  principally  of  a  membranous  or  fibrous  structure 
formed  into  distinct  layers,  and  composing  what  are  called  the 
coats  of  these  vessels.  The  number  of  these  coats  has  been 
differently  estimated  by  different  anatomists ;  but  it  is  now 
generally  agreed  that  those  proper  to  the  vessels  themselves  are 
principally  three :  the  external,  the  internal,  and  the  middle,  or 
what  has  been  called  the  muscular  coat.  Besides  these  tunics, 
each  vessel  is  surrounded  by  a  loose  and  flocculent  cellular  sub- 
stance, which  connects  it  with  the  parts  through  which  it  passes, 
and  accompanies  it  in  its  whole  course;  but  this  substance,  being 
merely  a  continuation  of  the  cellular  substance  which  fills  up  all 
the  vacuities  of  the  body,  is  common  to  the  vessel  and  to  other 
parts,  ought  not  properly  to  be  considered  as  belonging  to  the 
former,  but  as  adventitious ;  although  some  anatomists  have 
dignified  it  with  the  title  of  the  cellular  coat. 

416.  The  first  proper  coat  of  the  vessel  is  the  external  coat, 
which  is  thicker  than  the  rest,  and  formed  of  a  membranous 
structure,  in  which  are  intermixed  a  few  filaments  of  fibro-cellular 
substance,  disposed  obliquely  with  respect  to  the  course  of  the 
vessel,  and  interwoven  with  the  membranous  fibres.  The  inner- 
most membrane  is  thinner  than  the  former,  of  a  whiter  colour, 
more  or  less  pellucid,  and  presenting  a  more  uniform  homogene- 
ous structure.  Its  inner  surface  is  perfectly  smooth,  and  much 
resembles  in  appearance  the  serous  membranes.  Between  these 
membranous  coats,  there  exists  a  layer  of  fibres,  which  have 
been  generally  supposed  to  be  muscular,  constituting  what  has 
been  accordingly  called  the  muscular  coat.  Compared  with  the 
diameters  of  the  vessels,  these  coats  are  proportionably  thicker 
in  the  smaller  than  in  the  larger  vessels. 

417.  After  giving  this  general  description  of  the  structure  of 
the  blood-vessels,  we  proceed  to  notice  some  of  the  peculiarities 
which  distinguish  each  class  of  blood-vessels. 

3.  Arterial  System. 

418.  Each  of  the  great  arterial  trunks,  belonging  respectively 


CIRCULATION    OP    THE    BLOOD.  191 

to  the  aortic,  and  to  the  pulmonic  systems,  are  furnished,  at  their 
origin  from  the  ventricles  of  the  heart,  with  valves  of  a  semilunar 
shape,  adhering  by  one  of  their  sides  to  the  margin  of  the  aper- 
ture of  the  ventricle,  or  mouth  of  the  artery,  and  having  their 
loose  edges  turned  towards  the  axis  of  the  artery.  These  valves 
are  formed  by  a  duplicature  of  the  internal  coat,  which  contains 
between  their  folds  a  thin  layer,  of  ligamentous  fibres,  giving 
them  considerable  strength.  No  valves  are  found  in  any  other 
part  of  the  arterial  system. 

419.  The  external  coat  of  an  artery  is  formed  by  a  dense 
tissue  of  fibres,  which  are  interwoven  together  in,  different  direc- 
tions, generally  very  obliquely  with  regard  to  the  length  of  the 
vessel.  This  texture  becomes  more  compact  as  we  trace  it 
towards  the  interior,  so  that  the  individual  fibres  can  with  diffi- 
culty be  distinguished,  unless  by  a  forcible  tearing  asunder  of  the 
substance  they  compose.  Hence  the  older  anatomists  have  dis- 
tinguished this  inner  layer  of  the  external  coat,  as  forming  a 
separate  tunic,  to  which  they  have  given  the  name  of  the  nervous 
coat,  implying  thereby  a  participation  in  the  structure  of  ten- 
dons which  were  not  at  that  time  distinguished  from  nerves. 
The  division  of  the  external  coat  into  these  two  layers,  is  well 
marked  in  the  larger  arteries ;  but  in  proportion  as  we  examine 
the  smaller  branches,  we  find  a  more  uniform  appearance,  the 
whole  assuming  the  firm  and  compact  texture  of  fibrous  mem- 
branes. This  portion  of  the  arterial  structure  is  exceedingly  strong 
and  elastic,  both  with  respect  to  a  force  stretching  it  in  the  direc- 
tion of  its  length,  and  also  transversely,  or  in  that  of  its  diameter. 
Its  toughness  is  such  that  it  is  not  easily  cut  asunder  by  a  thread 
employed  as  a  ligature  upon  the  vessel. 

420.  The  intermediate,  or  muscular  membrane,  is  of  consider- 
able thickness,  has  a  yellow  colour,  and  is  composed  of  fibres, 
all  of  which  are  arranged  circularly ;  that  is,  in  the  circumfer- 
ence of  the  cylinder.  In  the  large  arterial  trunks,  these  fibres 
form  a  distinct  layer  or  tunic ;  but  the  membrane  acquires  a  still 
greater  proportional  thickness  in  the  smaller  branches,  and  then 
admits  of  subdivision,  by  dissection  into  several  layers.  The 
exterior  layers  are  less  dense  than  the  interior ;  and  those  which 
are  innermost  are  the  densest  of  all.  The  elasticity  and  firmness 
of  this  coat  is  chiefly  in  the  direction  of  the  circular  fibres  of 
which  it  consists ;  so  that  it  opposes  considerable  resistance  to 
any  force  which  tends  to  dilate  the  vessel,  but  yields  readily  to 
any  power  applied  for  its  elongation.  It  may  be  considered  as 
partaking  of  the  properties  of  muscular  and  ligamentous  struc- 
tures. 

421.  The  internal  membrane  of  arteries,  which  has  also  been 
called  the  nervous,  arachnoid,  or  common  coat,  is  the  thinnest  of 
the  three ;  |Jthough  still,  in  the  larger  arteries,  it  admits  of  divi- 


192  NUTRITIVE    FUNCTIONS. 

sion  into  two  or  more  layers.  The  innermost  of  these  is  ex- 
tremely thin  and  transparent,  and  its  surface  is  smooth  and 
highly  polished,  in  order  that  no  resistance  may  be  opposed  to 
the  motion  of  the  blood,  The  outer  portions  are  white  and 
opaque,  and  pass  gradually  into  the  substance  of  the  muscular 
tunic  with  which  it  is  connected.  Its  elasticity  is  very  small, 
and  its  power  of  resistance  is  limited,  so  that  a  ligature  applied 
on  the  vessel  generally  produces  a  laceration  of  the  internal  coat, 

422.  The  general  form  of  the  arterial  system,  if  it  were  iso- 
lated from  all  other  parts,  would  resemble  two  trees,  the  trunks 
of  which  would  be  constituted  by  the  aorta,  and  by  the  pulmo- 
nary artery,  and  which  divide  and  subdivide  successively  into 
smaller  and  smaller  branches,  till  they  arrive  at  an  extreme  de- 
gree of  tenuity.  Each  portion  which  intervenes  between  these 
divisions  preserves  the  same  uniform  diameter,  and  is,  therefore 
exactly  cylindrical.  Each  branch  is  of  course  smaller  than  the 
trunk  from  which  it  arises ;  but  the  sum  of  the  areas  of  all  the 
branches  into  which  an  artery  divides  itself,  is  in  general  greater 
than  the  area  of  that  artery ;  and  consequently  the  total  capacity 
of  the  arterial  system  is  progressively  inci'easing  in  proportion  to 
the  number  of  subdivisions  which  take  place.  Hence  the  whole 
system  may  in  reality  be  considered  as  composing  a  conical 
cavity,  of  which  the  aorta  is  the  apex,  and  the  ultimate  subdivi- 
sions the  base.'  The  number  of  subdivisions  in  the  whole  course 
of  an  artery  scarcely  ever  exceeds  twenty,  according  to  the  esti- 
mate of  Haller,  who  took  pains  to  ascertain  this  point.  The  most 
usual  mode  of  ramification  is  that  of  bifurcation,  or  division  of  a 
trunk  into  two  branches,  which  generally  form  between  them  an 
acute  angle.  In  some  instances,  especially  among  the  larger 
arteries,  we  meet  with  a  branch  sent  off  at  right  angles  from  the 
main  trunk,  or  still  more  rarely  at  an  obtuse  angle. 

423.  Arteries  have  numerous  communications  among  their 
different  branches.  These  communications,  or  anastomoses,  as 
they  are  called,  are  effected  sometimes  by  the  re-union  of  two 
arteries  of  nearly  equal  size,  which  happen  to  be  proceeding  in 
similar  directions,  so  as  to  compose  one  common  trunk,  which 
proceeds  in  an  intermediate  direction,  sometimes  by  collateral 
branches  proceeding  obliquely  from  the  one  to  the  other ;  while 
on  other  occasions,  arteries  unite  from  greater  distances,  so  as  to 
form  a  wide  arch,  in  which  each  appears  to  be  continuous  one 
with  the  other;  and  from  the  convex  side  of  which,  branches  are 
again  sent  off,  which  are  distributed  in  minuter  ramifications.  In 
some  parts  the  anastomoses  are  so  frequent  and  numerous,  as  to 
resemble  a  net-work,  or  plexus  of  vessels. 

424.  The  principal  arteries  of  the  limbs  are  generally  found 
running  in  situations  where  they  are  best  protected  from  injury, 
and  where  they  are  most  secure  from  pressure  during  the  actions 


CIRCULATION    OF   THE    BLOOD.  193 

of  the  muscles.     Hence  they  are  chiefly  met  with  in  the  hollow 
spaces  formed  on  the  inner  side  of  the  flexures  of  the  joints. 

4.  Venous  System. 

425.  The  chief  peculiarities  in  the  structure  of  the  veins,  as 
distinguished  from  that  of  the  arteries,  consist  in  the  greater 
thinness,  and  diminished  density  of  their  coats,  the  tenuity  or  ab- 
sence of  the  muscular  tunic,  and  the  numerous  valves  which 
occur  in  different  parts  of  their  course.  The  outer  coat  resem- 
bles that  of  the  arteries,  but  does  not  present  so  dense  or  so  fine 
a  texture  of  fibres;  and  it  possesses  less  absolute  strength.  The 
middle  coat  is  formed  of  fibres  which  are  more  extensile  and 
flexible  than  those  of  arteries ;  and  their  direction,  instead  of  be- 
ing transverse,  is  principally  longitudinal.  These  fibres  are  not 
constantly  met  with  in  all  the  parts  of  the  venous  system,  but 
vary  much  in  their  proportion  to  the  rest  of  the  structure  in  dif- 
ferent veins,  as  well  as  in  their  directions  and  thickness.  It  is 
only  in  the  large  veins,  near  the  heart,  that  this  coat  presents 
any  appearance  of  muscular  fibres.  The  inner  coat  is  thin  and 
transparent,  like  that  of  the  arteries  ;  but  difl^ers  from  the  latter 
in  being  more  extensible,  less  easily  torn,  and  in  its  containing  a 
certain  proportion  of  ligamentous  fibres  in  its  composition.  Some 
of  the  veins,  such  as  those  within  the  cranium,  which  are  called 
sinuses,  as  well  as  the  veins  which  traverse  the  bones,  being  pro- 
tected by  the  surrounding  parts,  appear  to  consist  altogether  of 
this  inner  coat,  and  are  unprovided  with  either  the  muscular  or 
the  cellular  coats. 

426.  The  large  veins  follow  in  general  the  course  of  the  arte- 
ries, but  are  usually  twice  as  numerous ;  so  that  where  we  meet 
with  an  artery,  we  generally  find  it  accompanied  by  two  veins. 
Their  general  disposition  is  arborescent,  like  the  arterial  system  ; 
but  with  reference  to  the  function  they  perform,  they  may  be 
more  aptly  compared  to  the  roots  than  to  the  branches  of  a  tree  ; 
for  in  following  the  course  of  the  blood  in  its  circulation,  they 
may  be  said  to  take  their  rise  from  the  minutest  vessels,  and  suc- 
cessively uniting  into  larger  and  larger  tubes,  to  terminate  by  one 
or  two  main  trunks  in  the  heart.  The  total  capacity  of  the 
venous  system  is  at  least  twice  as  great  as  that  of  the  arterial 
system.  The  distribution  and  general  mode  of  ramification  of 
the  veins,  correspond  very  exactly  to  that  of  the  arteries,  pre- 
senting the  same  ramified  appearance,  and  the  same  frequent 
anastomoses.  These  collateral  communications  are  exceedingly 
numerous  in  the  superficial  veins,  and  wherever  they  are  liable 
to  partial  obstruction  from  external  pressure.  It  is  in  these  situa- 
tions also,  that  we  meet  with  a  great  number  of  valves  in  the 
course  of  the  veins.     The  veins  of  the  deep-seated  organs  are 

17 


194  NUTRITIVE    FUNCTIONS, 

generally  unprovided  with  valves  in  any  part  of  their  course. 
The  arteries,  as  we  have  already  seen,  have  no  valves  except  at 
their  commencement. 

427.  Besides  the  two  venous  systems  appropriated  to  the 
greater  and  lesser  circulations,  the  former  uniting  in  the  venae 
cavag,  and  the  latter  in  the  pulmonary  veins,  and  therefore  cor- 
responding to  the  two  arterial  systems,  there  is  also  another,  and 
more  partial  system  of  veins,  peculiar  to  the  circulation  in  the 
liver,  and  other  viscera  of  the  abdomen.  This  particular  system, 
which  is  that  of  the  vena  portce,  as  it  is  called,  is  complete  within 
itself;  that  is,  it  constitutes  a  tree,  having  a  common  stem,  with 
its  proper  roots  and  branches,  the  whole  of  which  is  placed  as 
an  intermediate  system  between  the  ultimate  branches  of  the 
gastric,  intestinal,  and  splenic  arteries,  of  which  the  roots  of  the 
vena  porta?  may  be  considered  as  the  continuations,  and  first 
radicles  of  the  proper  hepatic  veins,  which  are  the  continuations 
of  the  ultimate  ramifications  of  the  vena  portas.  By  this  arrange- 
ment, the  blood  which  has  circulated  through  the  stomach,  the 
intestines,  and  the  spleen,  is  distributed  by  a  new  set  of  veins, 
throughout  the  substance  of  the  liver,  and  is  returned  to  the 
general  mass  of  blood  in  the  vense  cavee,  after  circulating  through 
that  organ.  ^ 

To  this  pecuUar  venous  system  there  is  no  corresponding  arte- 
rial system. 

5.   Capillary  System. 

428.  The  ultimate  ramifications  of  the  arteries,  as  well  as  the 
beginnings  of  the  veins,  are,  in  almost  every  part  of  the  body, 
vessels  of  such  extreme  tenuity,  as  to  be  imperceptible  wdthout 
the  assistance  of  the  microscope ;  and  they  cannot  even  then  be 
discerned,  unless  the  part  be  artificially  prepared  by  the  injec- 
tion of  some  coloured  substance  into  the  vessels,  or  unless  they 
have  been  accidentally  enlarged  by  disease,  so  as  to  have 
received  the  colouring  matter  of  the  blood.  Hence  the  ancients, 
who  were  ignorant  both  of  the  art  of  injecting,  and  of  the  power 
of  the  microscope,  were  precluded  from  a  knowledge  of  the 
existence  of  these  minute  vessels.  They  believed  that  a  sub- 
stance, which  they  termed  parenchyma,  and  which  they  con- 
ceived to  be  of  a  spongy  texture,  was  interposed  between  the 
terminal  branches  of  the  arteries,  and  the  beginning  of  the  veins ; 
and  this  opinion  was  adopted  almost  universally  by  anatomists 
before  the  epoch  of  the  discovery  of  the  circulation,  and  has 
been  entertained  even  after  this  period,  by  a  great  number  of 
eminent  anatomists,  down  to  the  present  day.  But  the  injections 
of  Ent,  and  the  microscopical  observations  of  Malpighi  and  of 
Leewenhoek,  have  sufficiently  demonstrated  the  continuity  of 


CIRCULATION    OF    THE    BLOOD.  195 

the  canals  by  wliich  the  blood  is  made  to  pass  from  the  arteries 
into  the  veins.  The  researches  of  modern  anatomists,  indeed, 
by  showing  the  amazing  extent  to  which  the  minute  division  of 
the  vascular  system  is  curried,  and  in  which  they  pervade  every 
part  of  the  frame,  have  finally  exploded  the  hypothesis  of  the 
existence  of  interposed  parenchyma,  and  have  given  rise  -to 
another  hypothesis  of  an  opposite  kind,  namely,  of  all  the  textures 
of  the  body  being  ultimately  resolvable  into  vessels. 

429.  The  name  of  capillary  vessels  is  given  to  those  minute 
branches  of  either  arteries  or  veins,  whose  diameter  is  finer  than 
a  hair,  and  which  can  therefore  scarcely  be  distinguished  by  the 
unassisted  eye.  Authors  have  endeavoured  to  establish  three 
gradations  of  size  in  this  class  of  vessels ;  the  largest  being  those 
"which  can  be  but  just  perceived  by  the  eye  without  a  magnifying 
glass ;  the  next,  those  which  require  the  aid  of  the  microscope 
for  their  detection  ;  and  the  third,  those  which  are  capable  of 
admitting  only  a  single  red  globule  of  blood,  and  of  which  the 
calibre  must  consequently  be  only  a  very  little  larger  than  these 
globules. 

430.  The  larger  capillaries  undergo  several  subdivisions  in 
their  course,  before  they  arrive  at  this  extreme  degree  of  tenuity; 
and  indeed,  their  lateral  branches  of  communication  are  so  mul- 
tiplied as  they  proceed,  that  the  whole  forms  a  general  and 
extensive  net-work  of  vessels.  The  total  capacity  of  .the  capillary 
system  far  surpasses  that  of  the  arteries  and  veins;  and  they 
contain  therefore  by  much  the  greatest  portion  of  the  blood  in 
the  natural  and  healthy  state  of  the  circulation. 

431.  The  vascular  branches  which  form  the  channels  of  com- 
munication between  the  arteries  and  the  veins,  are,  with  but  very 
few  vexceptions,  referable  to  the  class  of  capillary  vessels.  In 
this  continuous  course  it  is  scarcely  possible  to  mark  with  preci- 
sion, at  what  point  the  arterial  portion  may  be  said  to  terminate, 
and  the  venous  portion  to  commence.  Neither  the  limit  of  size, 
nor  the  change  of  direction,  is  sufficient  to  lay  the  foundations  of 
such  a  distinction;  for  the  alteration  of  diameter  is  gradual,  and 
the  inflexions  are  various,  and  frequently  tortuous,  so  that  no  de- 
terminate criterion  can  be  assumed  as  characteristic  of  either 
artery  or  vein.  Hence  arises  the  propriety  of  constituting  a 
distinct  class  of  capillary  vessels. 

432.  The  texture  of  the  capillaries,  from  the  minuteness  of 
their  size,  scarcely  admits  of  accurate  observation.  Their  coats 
are  thin,  soft,  pellucid,  and  therefore  invisible  to  the  naked  eye, 
and  hardly  discernible  with  the  microscope.  It  is  most  probable 
that  they  are  formed,  in  every  instance,  by  a  prolongation  of  the 
internal  coats  of  the  larger  arteries  and  veins  with  which  they 
are  continuous.* 

*  [It  would  not  be  easy  to  account  for  the  phenomena  of  nutrition,  unless 


196  NUTRITIVE    FUNCTIONS. 

433.  As  the  capability  of  admitting  coloured  substances  is  ap- 
parently an  indispensable  condition  for  their  being  visible,  the 
existence  of  vessels  of  still  smaller  diameter,  containing  only 
colourless  fluids,  must  more  or  less  be  matter  of  conjecture.  A 
very  great  number  of  anatomists  and  physiologists,  however, 
among  whom  may  be  enumerated  Boerhaave,  Vieussens,  Farrie- 
nus,  Haller,  Soemmerring,  Bichat,  Bleuland,  Chaussier,  have 
admitted  the  existence  of  another  order  of  capillaries,  or  serous 
vessels,  as  they  have  termed  them,  of  which  the  diameter  is  too 
small  to  admit  even  a  single  red  globule,  and  which  therefore 
circulate  only  the  serous  part  of  the  blood.  On  the  other  hand, 
the  reality  of  these  pi'etended  vessels  is  contested  by  Prochaska, 
Mascagni,  Richerand,  and  others.  Beclard,  in  his  Anatomie 
Genirale,  has  given  a  review  of  the  arguments  employed  on  both 
sides  in  this  controversy,  which  is  by  no  means  as  yet  set  at  rest, 
and  which  will  probably  have  to  be  decided,  more  by  considera- 
tions of  a  physiological  than  of  an  anatomical  nature. 

434.  In  speaking  of  the  communications  between  the  arteries 
and  the  veins,  it  remains  only  to  be  noticed,  that  in  many  parts 
of  the  body  there  appears  to  be  interposed  between  the  extreme 
branches  of  each,  a  spongy  or  cellular  structure,  into  which  the 
arteries  occasionally  pour  out  blood,  so  as  to  distend  these  cells, 
and  from  which  the  veins  arise  by  open  orifices,  and  absorb  the 
blood,  in  order  to  unload  the  cells,  and  remove  the  accumulation 
which  has  taken  place.  Such  a  structure  has  been  denominated 
the  erectile  tissue.  It  is  exemplified  on  a  large  scale,  in  the  spleen, 
and  in  some  of  the  sexual  organs.  We  shall  notice  this  struc- 
ture afterwards. 

435.  The  different  parts  and  textures  of  the  body  are  supplied 
with  vessels  in  very  different  proportions.  The  organs  which 
rank  first  in  respect  to  its  vascularity,  is  the  lungs ;  after  which 
come  the  integuments,  the  pia  mater,  and  choroid  coat  of  the 
eye;  next  the  glands,  the  glandular  follicles,  the  lymphatic  glands, 
the  cortical  substance  of  the  brain,-  the  nervous  ganglions.  To 
these  will  succeed  in  the  order  of  vascularity,  the  muscles,  the 

we  were  to  presume  that  some  part  of  the  capillary  or  intermediate  system 
consists  of  coatless  or  merabraneless  tubes;  and  that,  in  the  passage  of  the  blood 
through  them,  the  different  tissues  may  act  on  the  blood  and  conversely.  The 
mode,  indeed,  in  which  the  blood  is  distributed  through  the  tissues  may  not  be 
inaptly  compared  to  that,  by  which  the  water  of  a  river  is  distributed  through 
a  marsh,  conveying  to  the  vegetable  bodies  that  flourish  on  its  surface,  the 
materials  for  their  nutrition.  Wedemeyer,  Gruithuisen,  Dollinger,  Cams,  and 
others,  consider  that  the  blood  is  contained  in  the  different  tissues,  or  channels, 
which  it  forms  in  them  :  even  under  the  microscope,  the  stream  is  seen  to 
work  out  for  itself,  easily  and  rapidly,  a  new  passage  in  the  tissues,  which  it 
penetrates;  and  it  seems  certain,  that  in  the  figura  venosa  of  the  egv,  the 
blood  is  not  surrounded  by  vascular  parietes.  See,  on  all  this  subject, 
Dunglison's  Physiology,  3d  edit.  ii.  154,  and  206.] 


PHENOMENA    OF    THE    CIRCULATION.  197 

periosteum,  the  adipose  tissue,  the  medullary  nervous  substance, 
the  bones,  and  the  serous  membranes.  The  tehdons  and  liga- 
ments are  amongst  the  least  vascular  parts.  Still  less  so  are  the 
cartilages,  and  the  arachnoid  membrane  of  the  brain;  and  lastly, 
the  epidermis,  and  its  appendages,  as  the  nails  and  hair,  together 
with  the  enamel  of  the  teeth,  maybe  considered  as  parts  entirely 
devoid  of  vessels. 

,  436.  The  actual  mass  of  blood  which  the  organs  of  the  circu- 
lation have  lo  move  through  the  channels  we  have  just  pointed 
out  has  been  variously  estimated  by  different  physiologists.  The 
lowest  computation  is  that  of  Moulins  and  Abeildgaard,  who 
made  it  out  to  be  only  eight  pounds.  Borelh  estimated  it  at 
twenty  pounds ;  Planche  at  twenty-eight ;  Haller  at  thirty;  Dr. 
Young  at  forty;  Hamberger  at  eighty;  and  Keil  at  one  hundred. 
Blumenbach  states  the  propoi'tion  in  an  adult  healthy  man  to  be 
one-fifth  of  the  entire  weight  of  the  body ;  but  Dr.  Good,  who 
has  collected  these  authorities,  is  disposed  to  place  but  Uttle  reli- 
ance on  the  latter  mode  of  estimation,  on  account  of  the  great 
diversity  in  point  of  weight  and  bulk  of  adults,  whose  aggregate 
quantity  of  blood  would  appear  to  be  nearly  the  same.  He 
thinks  the  mean  of  the  above  numbers,,  which  is  between  thirty 
and  forty  pounds,  may  safely  be  taken  as  nearest  to  the  truth. 
The  proportions  of  the  whole  mass  of  blood  which  is  contained  in 
different  parts  of  the  vascular  system,  varies  according  to  age. 
In  early  life,  there  is  nearly  an  equal  quantity  contained  in  the 
arteries  as  in  the  veins.  In  the  adult,  one-fourth  only  is  contained 
in  the  arterial,  and  three-fourths  in  the  venous  system  ;*  and  the 
disproportion  is  greater  as  age  advances. 


Sect.  II. — Phenomena  of  the  Circulation. 
1.  Course  of  the  Blood  in  its  Circulation. 

437.  Having  premised  this  general  outline  of  the  course  which 
the  blood  takes  during  its  circulation,  we  shall  now  follow  the 
several  steps  more  in  detail,  examining,  as  we  proceed,  the 
evidence  afTorded  us  that  such  is  its  real  course ;  and  we  shall  lastly 
inquire  into  the  several  powers  concerned  in  its  propulsion. 

438.  We  shall,  for  this  purpose,  begin  at  that  part  of  its  circuit 
at  which  the  blood  is  brought  back  from  the  lungs,  after  receiving 
the  vivifying  influence  of  the  air,  and  being  thereby  arterialized, 
as  it  has  been  called.  The  pulmonary  veins,  which  convey  it  in 
this  state  to  the  heart,  are  collected  into  four  great  trunks,  which 

*  [The  general  approximation  is  one  third  in  the  arteries,  and  two  thirds  in 
the  veins.  Haller  estimated  that  the  arterial  blood  is  to  the  venous  as  four 
to  nine.] 

17* 


198  NUTRITIVE    FUNCTIONS. 

'  open  into  the  left  auricle  of  the  heart.  As  soon  as  the  auricle  is 
distended  beyond  a  certain  degree  by  this  flow  of  blood  into  it,  it 
contracts  and  pours  the  whole  of  its  contents  at  once  into  the  left 
ventricle.  The  constant  stream  of  blood  which  is  flowing  towards 
the  auricle  from  the  lungs,  prevents  any  portion  of  the  blood  of  the 
auricle  from  flowing  back  into  them  when  the  auricle  contracts. 
No  sooner  has  the  ventricle  received  this  blood,  which  has  passed 
into  it  by  a  sudden  influx,  than  it  is  stimulated  to  a  vigorous 
contraction  of  its  muscular  fibres,  which,  surrounding  the  cavity 
in  a  spiral  direction,  contract  its  cavity,  and  exerting  a  powerful 
pressure  on  the  contained  fluid,  propels  it  with  prodigious  force 
into  the  aorta.  The  contraction  of  the  ventricle  is  attended  with 
the  raising  of  the  mitral  valve,  interposed  between  it  and  the 
auricle,  and  the  sides  of  that  valve  being  closely  applied  to  the 

'  aperture  by  which  the  blood  had  entered  the  ventricle,  all  return 
of  the  blood  into  the  auricle  is  thereby  prevented.  The  whole  of 
it  rushes,  therefore,  as  an  impetuous  torrent  into  the  aorta,  or 
main  trunk  of  the  arterial  system.  The  blood  which  has  entered 
the  artery  is  again  prevented  from  flowing  back  into  the  ventricle^ 
by  a  valvular  apparatus  of  the  same  kind  as  that  which  occurs 
between  the  auricle  and  the  ventricle.     These  valves,  placed  at 

-  the  entrance  of  the  aorta,  are  called  the  sigmoid,  or  semilunar 
valves.  They  are  three  in  number,  each  being  attached  by  its 
convex  edge  to  the  coats  of  the  artery,  to  which  it  is  closely 
applied  when  the  stream  of  blood  is  flowing  in  a  direction  from 
the  heart,  but  which  is  immediately  raised,  and  the  three  loose 
edges  joining  together,  form  a  complete  barrier  to  the  passage  of 
the  blood  when  moving  in  the  contrary  direction.* 

439.  The  blood,  having  passed  into  the  aorta,  is  conveyed 
through  its  branches  and  ramifications  to  all  the  parts  where 
these  ramifications  extend,  till  it  reaches  the  capillaries,  where 
it  moves  more  slowly,  yet  still  proceeds  on  its  course,  supplying 
every  part  with  the  materials  necessary  for  the  maintenance 
of  their  nutrition  and  vital  powers.  From  the  capillaries  the 
blood  is  brought  back  by  the  minuter  branches  of  the  veins, 
which,  uniting  successively  to  form  larger  and  larger  trunks, 
are  at  length  collected  into  the  two  vense  cavee,  the  one  descend- 
ing from  the  head  and  superior  parts  of  the  body,  and  the  other 
ascending  from  the  inferior  parts,  and  both  joining  at  the  right 
auricle  of  the  heart.  The  same  process  now  takes  place  in  the 
right  cavities  of  the  heart,  which  was  described  as  occurring  in 
the  left.     The  rifjht  auricle  is  filled  with  blood  from  the  venag 

*  [The  use  of  the  sinuses  or  dilatations  immediately  abovp  these  valves,  is  to 
prevent  them  from  being  so  closely  applied  to  the  sides  of  the  vessel,  that  the 
reflupnt  blood,  during  the  diastole  of  the  ventricles,  cannot  readily  strike  them 
so  as  to  depress  them.] 


PHENOMENA    OF    THE    CIRCULATION.  199 

cavae ;  it  contracts*  and  pours  its  contents  into  the  cavity  of  the 
right  ventricle,  which,  being  in  its  turn  stimulated  to  contract, 
propels  the  blood  it  had  received  from  the  auricle  into  the  trunk 
of  the  pulmonary  artery ;  which  artery  likewise  distributes  it,  by 
a  similar  system  of  ramifications,  to  the  membrane  lining  the  air 
vesicles  of  the  lungs.  All  retrograde  motion  of  the  blood  is  pre- 
vented as  efiectually  in  this  case  as  in  the  former,  by  the  interpo- 
sition of  the  tricuspid  valves  between  the  auricle  and  ventricle, 
and  by  the  semilunar  valves  placed  at  the  entrance  of  the  pulmo- 
nary artery.f 

440.  From  the  ultimate  ramifications  of  the  pulmonary  artery 
the  blood  is  conducted  into  the  capillary  vessels,  which  are  spread 
over  the  membrane  of  the  air-cells  of  the  lungs,  where  it  under- 
goes the  change  of  quality  from  venous  to  arterial,  consequent 
upon  its  exposure  to  the  chemical  action  of  the  oxygen  which  is 
contained  in  the  atmospheric  air  admitted  into  those  cells.  From 
these  capillaries  it  is  collected  by  the  pulmonary  veins,  and  re- 
turned, as  before  stated,  to  the  heart,  to  be  again  distributed  to 
every  part  of  the  body. 

441.  Whilfe  one  portion  of  the  blood  is  circulating  in  the  sys- 
tem, another  portion  is  circulating  in  the  lungs.  Both  auricles 
are  filled  at  the  same  moment,  and  contract  together ;  each  send- 
ing its  blood  into  the  corresponding  ventricle.  In  Uke  manner,  the 
two  ventricles  contract  simultaneously,  and  propel  their  contents 
into  their  respective  arterial  trunks.  The  contraction  of  the 
heart  is  called  the  systole ;  its  relaxation  the  diastole. 

G.  Proofs  of  the  Circulation. 

442.  The  discovery  of  the  course  which  the  blood  takes  in 
its  circulation,  a  discovery  of  such  vast  magnitude,  that  almost 
the  whole  of  the  present  doctrines  of  physiology  and  pathology 
are  either  directly  founded  on  it,  or  are  more  or  less  immediately 
related  to  it,  was  made  in  the  beginning  of  the  seventeenth  century. 
It  was  one  of  the  earliest  fruits  of  that  active  spirit  of  inquiry, 
and  rational   process  of  investigation,  which,  since  the  era  of 

"  [There  is  great  reason  for  the  belief,  both'from  anatomy,  and  the  evidences 
afforded  by  ocular  inspection  of  the  living  heart  whilst  in  action,  that  too  much 
importance  has  been  assigned  to  the  energetic  contraction  of  the  auricles.  It 
appears  indeed  probable,  that  the  great  use  of  the  auricles  is  to  act  as  tnie 
sinuses  or  gulfs,  for  the  reception  of  the  blood  proceeding  from  every  part  of 
the  body,  and  that  little  effect  is  produced  on  the  circulation  by  their  varying 
condition.     Dunglison,  Op.  cii.  ii.  159.], 

f  [The  action  of  the  tricuspid,  in  this  respect,  is  not  as  perfect  as  that  of  the 
mitral  valve.  It  seems,  indeed,  to  be  destined  to  permit  a  certain  degree  of 
reflux;  and  in  this  M^ay,  perhaps,  to  be  a  provision  against  the  mischief  that 
might,  under  certain  circumstances,  result  from  an  excessive  afflux  of  blood 
to  the  lungs:  the  tricuspid  thus  acting  as  a  safety  valve.  Mr.  King,  Guy's 
Hospital  Reports,  No.  IV.    April,  1837.] 


200  NUTRITIVE    FUNCTIONS. 

Bacon  was  beginning  to  diffuse  itself  in  Europe.  It  was  an  honour 
reserved  for  our  illustrious  countryman  Harvey,  whose  fame  must 
live  as  long  as  science  is  cherished  among  men.  While  it  is  the 
fate  of  other  discoveries,  that  their  authors  are  either  soon  for- 
gotten, or  only  known  to  a  small  class  of  those  who  devote  their 
attention  peculiarly  to  the  subject  to  which  they  relate,  the  name 
of  Harvev  is  become  familiar  to  all  who  have  any  acquaintance 
with  general  literature,  or  pretensions  to  a  liberal  education. 
However  firmly  the  truth  of  his  great  discovery  be  established 
in  the  present  time,  it  was,  in  its  first  promulgation,  keenly  con- 
tested by  many  contemporary  physiologists.  To  us  who  have 
no  such  prejudices  to  warp  our  judgment,  and  who  are  furnished 
with  so  large  a  body  of  evidence  on  the  subject,  the  controversy 
appears  exceedingly  frivolous  and  absurd.  Yet  we  must  recol- 
lect that  in  every  subject  of  human  opinion,  it  requires  a  consider- 
able time  to  wean  mankind  from  errors  which  have  been  long 
and  deeply  rooted  in  their  minds,  however  palpable  such  errors 
may  appear  to  the  eyes  of  those  who  have  not  been  so  blinded. 
As  it  may  still,  however,  be  satisfactory  to  know  the  grounds 
upon  which  the  doctrine  is  founded,  we  shall  briefly  enumerate 
the  leading  facts  and  arguments  that  establish  it. 

443.  The  most  striking  proofs  that  the  course  of  the  blood 
along  the  arteries  is  from  the  heart  towards  the  extremities  of 
those  vessels,  and  along  the  veins  in  the  contrary  direction,  are 
obtained  from  ligatures  on  those  vessels.  If  any  of  the  larger 
arterial  branches  be  tied,  that  portion  of  the  vessel  which  is 
situate  between  the  ligature  and  the  heart,  immediately  swells, 
becomes  distended  with  blood,  and  exhibits  strong  pulsations ; 
and  if  while  in  this  state  it  be  punctured,  the  blood  rushes  out 
with  violence,  and  in  successive  jets,  corresponding  to  the  pulsa- 
tions of  the  heart.  The  part  beyond  the  ligature,  on  the  other 
hand,  or  that  farthest  from  the  heart,  is  flaccid  and  empty,  and 
affords  no  blood  when  divided  ;  it  is  also  void  of  pulsation.  Phe- 
nomena precisely  the  reverse  of  these  are  exhibited  when  similar 
experiments  are  made  on  the  veins;  in  them,  the  part  most  dis- 
tant from  the  heart  becomes  turgid,  while  the  nearer  part  is 
empty.  This  last  experiment  is  one  that  is  made  every  time  a 
person  undergoes  the  operation  of  blood-letting.  A  ligature  is 
applied  round  the  arm,  from  the  pressure  of  which  on  the  sub- 
cutaneous veins,  they  are  made  to  svv^eU  every  where  below  the 
ligature,  that  is,  farther  from  the  heart ;  while  all  the  veins  above 
the  ligature  are  empty,  the  blood  having  been  propelled  onwards 
in  its  course  towards  the  heart.  Those  parts  which  are  swelled 
pour  out  their  blood  profusely  on  being  punctured  ;  and  when  the 
bandage  is  removed,  the  flow  is  stopped,  in  consequence  of  the 
blood  finding  a  ready  passage  to  the  heart. 

444.  In  the  veins,  we  have  additional  evidence,  from  the  struc- 


PHENOMENA    OF    THE    CIRCULATION.  201 

ture  of  the  valves,  that  the  blood  can  move  only  in  one  direction, 
namely,  towards  the  heart.  The  valves  at  the  entrance  of  the 
ventricles  and  arterial  trunks,  which  allow  of  motion  only  in  a 
particular  course,  lead  to  a  similar  conclusion  with  respect  to  the 
direction  of  the  current  in  its  passage  through  the  heart.  It  is 
impossible  by  artificial  means  to  force  fluid  injections  through 
the  heart,  in  a  course  contrary  to  that  in  which  the  blood  moves  ; 
and  the  same  insuperable  resistance  is  experienced  in  the  attempt 
to  pass  injections  in  other  parts  of  the  circulating  system,  when 
in  opposition  to  the  natural  course  taken  by  the  blood,  while  the 
same  fluids  readily  find  their  way  from  the  arteries  into  the 
veins,  when  thrown  in  that  direction. 

445.  Ocular  demonstration  of  the  course  of  the  blood  while 
circulating  in  the  smaller  arterial  and  venous  branches,  and  also 
in  the  capillaries,  is  afforded  by  the  microscope,  when  a  very 
thin  and  transparent  membrane  in  which  such  vessels  are  distri- 
buted is  placed  in  the  field  of  a  good  microscope.  The  web  be- 
tween the  toes  of  a  frog,  the  surface  of  its  vesicular  lungs,  the 
mesentery,  the  membrane  in  the  tail  of  small  fishes,  are  all  of 
them  capable  of  exhibiting  these  phenomena,  and  present,  indeed, 
a  spectacle  of  the  highest  interest. 

'446.  The  successive  action' of  the  cavities  of  the  heart,  in  the 
order  above  enumerated,  may  also  be  seen  when  the  hearts  of 
living  creatures  are  exposed  to  view  ;  and  this  spectacle  may  be 
afforded  without  pain  to  the  animal,  if,  after  its  head  has  been 
completely  separated  from  the  body,  respiration  be  kept-  up  by 
artificial  means. 

447.  The  transfusion  of  the  blood  of  one  animal  into  the  ves- 
sels of  another  is  a  curious  illustration  of  the  doctrine  of  the 
circulation.  In  this  operation,  the  artery  of  one  animal  is  con- 
nected by  a  tube  with  the  vein  of  another  animal ;  the  conse- 
quence of  which  is  that  the  first  is  gradually  emptied  of  its  blood, 
while  the  vessels  of  the  other  are  in  a  state  of  repletion.  If  an 
opening  be  made  at  the  same  time  in  the  veins  of  this  second 
animal,  the  blood  originally  belonging  to  it  will  escape,  and  thus 
the  whole  mass  of  its  circulating  fluid  will  be  changed.  Experi- 
ments of  this  kind  were  at  one  time  very  common,  but  they 
have  long  ceased  to  excite  curiosity,  and  are  now  rarely  prac- 
tised.* 

That  the  blood  moves  with  great  rapidity  and  force  through 
the  larger  vessels,  is  proved  by  the  immense  quantity  that  is 
quickly  lost  if  any  great  artery  or  vein  be  wounded. 

*  [Transfusion  has  been  practised  by  Dr.  Blundell,  and  others,  in  cases  of 
extensive  uterine  hemorrhage,  where  life  has  been  ahnost  despaired  of,  and 
occasionally  with  good  eifeot.] 


202  NUTRITIVE    FUNCTIONS. 


Sect.  III. — Powers  concerned  in  the  Circulation. 

448.  We  have  next  to  inquire  into  the  nature  and,  magnitude 
of  the  forces  by  which  the  blood  is  impelled  in  its  course,  the  re- 
sistance opposed  to  its  progress,  and  the  general  laws  by  which 
its  movements  are  regulated. 

449.  The  subject  will  naturally  divide  itself  into  four  parts  ; 
namely,  as  relating  to  the  powers  of  the  heart,  of  the  arteries^  of 
the  capillaries,  and  of  the  veins. 

1.  Action  of  the  Heart. 

450.  The  intention  and  purpose  of  the  auricles,  which  are  placed 
as  ante-chambers  to  the  ventricles,  is  to  receive  the  blood  in  a 
constant  stream  from  the  veins,  which  fill  it  gradually  and  equa- 
bly, so  that  when  the  distension  has  reached  a  certain  degree, 
the  auricle  may  contract*  and  discharge  the  whole  of  its  contents 
with  a  sudden  impetus,  into  the  ventricle.  The  thickness  and 
muscular  force  of  the  auricles  are  very  inferior  to  those  of  the 
ventricles,  which  being  destined  to  propel  the  blood  with  consi- 
derable momentum  into  the  arterial  system,  are  exceedingly 
powerful,  but  seem  to  require  the  stimulus  of  a  sudden  and  forci- 
ble distension,  in  order  to  excite  them  to  a  sulRciently  energetic 
action.'  It  appears,  indeed,  that  this  mechanical  distension  and 
separation  of  their  sides  from  the  influx  of  fluid,  is  the  natural 
stimulus  that  excites  them  to  contraction ;  for  they  are  not  affected 
by  any  of  the  causes  which  produce  contractions  in  the  voluntary 
muscles,  such  as  irritation  of  the  nerves  which  supply  the  heart. 
On  the  other  hand,  the  mere  introduction  of  warm  water  into 
these  cavities,  when  previously  emptied  of  blood,  is  sufficient  to 
renew  the  action  of  the  heart.t 

451.  It  is  exceedingly  difficult  to  form  any  probable  estimate 
of  the  absolute  force  exerted  by  the  heart,  and  more  particularly 
by  the  left  ventricle,  in  propelling  its  contents.  No  inquiry  in 
physiology  was  pursued  with  more  ardour,  has  been  the  subject 
of  more  various  controversy,  or  has  given  rise  to  so  many  volu- 
'minous  and  elaborate  calculations. 

*  [See  §  457,] 

t  [The  organ  will  contract  and  relax  after  it  has  been  removed  from  the 
body.  In  the  case  of  a  monstrous  foetus,  its  motion  continued  for  some  time 
after  the  auricles  and  ventricles  were  laid  open  ;  the  organ  roughly  handled 
and  thrown  into  a.  basin  of  cold  water.  In  the  rattlesnake,  Dr.  Harlan  ob- 
served the  heart,  torn  from  the  body,  continue  its  contractions  for  ten  or  twelve 
hours;  and  Dr.  J.  K.  Mitchell  saw  the  heart  of  a  sturgeon  beat  until  the  sides 
rustled  from  dryness,  after  it  had  been  inflated  and  hung  up  to  dry.  Dungli- 
son's  Physiology,  ii.  169.] 


POWERS    CONCERNED    IN    THE    CIRCULATION.  203 

452.  It  will  be  quite  evident  that  a  very  considerable  power 
is  required,  in  order  to  enable  the  heart  to  propel  the  blood 
through  the  arteries,  when    we  consider  the   enormous   resis- 
tances  opposed   10  its  progress,  and  when  we  also  take  into 
account  the  great  velocity  given  to  it  in  its  motion.     The  co- 
lumn of  blood  already  contained  in  the  arterial  system,  must 
have   its   velocity  accelerated,  in    order  to   admit  of  the  pas- 
sage of  fresh  blood  into  the  aorta.     The   arteries  require  also  to 
be  distended  for  the  admission  of  this  additional  quantity  of  blood 
every  time  that  the  ventricle  contracts.     The  angles  and  flexures 
■which  the   blood  is  obliged  to  follow  in  its  course  through  the 
vessels,  must  be  causes  of  retardation,  and  must  be  productive  of 
a  loss  of  force,  which  the  muscular  power  of  the  heart  is  ulti- 
mately called  upon  to  supply.     The  operation  of  all  these  retard- 
ing causes  is  so   complicated,  that  we  need  not  be  surprised  at 
the  problem  of  the  force  exerted  by  the  heart,  having  baffled  the 
skill  of  the  best  mathematicians,  and  their  calculations  being  so 
widely  different  from  one  another.     Thus,  while  Keil  estimated 
the  power  of  the  left  ventricle  at  only  five  ounces,  Borelli  calcu- 
lated that  its  force  could  not  be  less  than  one  hundred  and  eighty 
thousand  pounds.     Dr.  Hales  computes  it  to  be  exactly  fifty-one 
pounds  and  a  half;  while  Tabor  concludes  its  amount  to  be  one 
hundred  and  fifty  pounds.     Such  irreconcilable  results  sufficiently 
show  the  futility  of  most  of  the  reasonings  on  which  they  are 
founded,  and  the  impossibility  of  making  any  satisfactory  approach 
towards  the  solution  of  the  problem.     We  should,  on  the  whole, 
be  more  disposed  to  place  confidence  in  the  estimate  of  Hales, 
who  moreover  states,  that  the  velocity  with  which  the  blood 
passes  into  the  aorta,  is  about  one  hundred   and  fifty  feet  per 
minute,  or  two  feet  and  a, half  per  second  ;  and  that  the  quantity 
of  blood  passing  through   the  heart  during  each  hour,  is  about 
twenty  times  the  whole  mass  of  blood  contained  in  the  body ;  or, 
in  other  words,  that  the  whole  mass  completes  twenty  entire  cir- 
culations in  an  hour.     The  great  velocity  of  the  blood  in  the 
vessels  is  exemplified  by  the  fact,  that  a  fluid  introduced  into  one 
of  the  jugular  veins  of  a  horse,  has  been  detected  in  the  opposite 
vein,  and  even  in  the  vena  saphena  of  the  leg,  in  the  course  of 
half  a  minute. 

453.  It  has  been  keenly  disputed  whether  the  heart  is  able 
completely  to  empty  its  cavities  at  each  contraction;  and  the 
question,  which  is  not  one  of  any  real  importance,  is  hardly  yet 
decided. 

454.  Another  subject  of  controversy  which  was  much  agitated 
among  the  French  physiologists  in  the  middle  of  the  last  cen- 
tury, is,  whether  the  heart  is  shortened  or  elongated  during  its 
systole ;  that  is,  whether  the  apex  approaches  the  base  during 
the  contraction  of  the  ventricle,  or  recedes  from  it.     From  the 


204  NUTRITIVE    FUNCTIONS. 

numerous  observations  of  Spallanzani,  as  well  as  of  other  experi- 
mentalists, there  seems  to  be  no  doubt  that  during  the  systole  all 
the  parts  are  brought  nearer  to  the  tendinous  ring  surrounding 
the  auriculo-ventricular  orifices,  which  may  be  regarded  as  the 
fixed  pivot  of  its  movements,  and  consequently  the  length,  as  well 
as  the  other  diameters  of  the  heart,  is  shortened.  During  this 
action,  however,  the  curvature  being  suddenly  straightened,  the 
apex  is  projected  forwards,  and  produces  that  striking  against 
the  ribs  which  is  felt  by  the  hand  applied  externally  to  the  chest.* 

455.  The  right  ventricle  having  only  to  perform  the  lighter 
task  of  circulating  the  blood  through  the  lungs,  is  much  inferior 
in  thickness  and  strength  to  the  left  ventricle,  which  has  to  pro- 
pel the  blood  through  the  whole  aortic  system,  forming  a  course 
of  much  greater  magnitude  than  that  of  the  pulmonary  vessels. 
But,  on  the  other  hand,  the  capacities  of  the  two  ventricles  are 
nearly  equal,  as  might  be  expected,  when  it  is  considered  that 
the  same  quantity  of  blood  which  is  forced  out  from  the  one, 
must,  in  the  course  of  circulation,  pass  through  the  other;  and 
that  both  the  ventricles  contract  the  same  number  of  times  in  a 
given  interval.  The  quantity  of  blood  expelled  by  the  heart  at 
each  contraction,  is  estimated  by  Blumenbach  at  two  ounces. 
So  that,  reckoning  the  whole  mass  of  blood  at  thirty-five  pounds, 
or  four  hundred  and  twenty  ounces,  and  the  contractions  to  be 
repeated  seventy-five  times  in  a  minute,  the  whole  of  the  blood 
will  have  passed  through  the  heart  in  about  three  minutes ;  thus 
agreeing  very  nearly  with  the  estimate  of  Hales  already  stated 
(§  452). 

456.  It  has  been  supposed  that  the  heart  exerts  some  force  in 
the  diastole  as  well  as  systole ;  and  that  the  recoil  of  the  mus- 
cles when  they  spring  back,  after  they  have  performed  their 
contraction,  creates  a  force  of  suction,  which  promotes  the  flow 
of  blood  in  the  great  veins  towards  the  heart.  But  the  truth  of 
this  proposition  is  exceedingly  dubious.f 

457.  The  movements  of  the  heart  are  completely  involuntary ; 
that  is,  are  entirely  beyond  the  control  of  the  will.  Nor  are  its 
natural  actions  accompanied  by  any  sensations.  They  are, 
generally  speaking,  totally  independent  of  the  nervous  system ; 
for  they  may  be  maintained  after  the  destruction  of  the  brain 
and  spinal  cord,  and  even  after  all  the  nerves  which  supply  the 

*  [This  is  one  view ;  but,  perhaps,  the  great  agency  is  the  expansive  force  of 
the  heart,  which  tends  to  project  it  forward.  It  must  be  admitted,  however,  with 
J.  Miiller,  (Physiology,  Baly's  Translation,  p.  175,)  that  great  uncertainty 
still  rests,  as  to  whether  the  impulse  is  produced  during  the  contraction  or  the 
dilatation  of  the  ventricles.] 

f  [The  existence  of  the  suction  power  of  the  heart  or  derivation,  although 
doubted  by  many,  appears  to  us  to  be  fully  established.  It  has  been  observed 
in  the  living  body  ;  and  the  observer  has  been  forcibly  struck  with  the  activity 
with  which  the  diastole  was  effected.     Dunglison,  Op,  cit,  ii.  182.] 


POWERS   CONCERNED    IN    THE    CIRCULATION.  205 

heart  have  been  divided.  Yet  these  movements  arc  capable  of 
being  influenced,  often  very  suddenly,  by  an  impression  made 
upon  any  considerable  portion  of  the  nervous  system.  The  regu- 
lar contractions  of  the  heart  appear  to  be  excited  simply  by  the 
stimulus  of  distension  from  the  periodical  influx  of  blood  into  its 
cavities.  This  organ  is  evidently  endowed  with  a  very  high 
degree,  and  a  very  peculiar  kind  of  irritability,  not  subject,  like 
that  of  the  voluntary  muscles,  to  exhaustion,  by  the  most  power- 
ful exertions,  reiterated  for  an  indefinite  time.* 

2.  Action  of  the  Arteries. 

458.  Whatever  be  the  velocity  with  which  the  blood  is  pro- 
jected from  the  heart  into  the  aorta,  that  velocity  is  soon  retarded, 
in  the  course  of  its  progress  from  the  larger  to  the  smaller  branches 
of  that  arterial  trunk.  This  is  amply  illustrated  by  the  observa- 
tion of  the  effects  which  follow  the  division  or  wounds  of  arte- 
ries in  difterent  parts  of  their  course.  A  wound  of  the  carotid 
artery  is  almost  instantly  fatal,  from  the  deluge  of  blood  which 
rushes  out  from  the  opening.  The  division  of  the  other  large 
arterial  trunks  is  no  less  certainly  fatal,  if  means  be  not  at  hand 
to  stop  the  torrent  that  gushes  out  with  resistless  impetuosity. 
In  the  smaller  arteries,  such  as  those  in  which  the  motion  of  the 
blood  can  be  viewed  with  the  microscope,  the  current  is  very 
languid  and  feeble.  It  is,  in  reality,  however,  much  slower  than 
it  appears  to  be  ;  for  it  should  be  recollected,  that  in  viewing  the 
magnified  image  of  an  object,  its  motion  is  magnified  in  the  same 
proportion  as  its  dimensions. 

459.  The  cause  of  this  continual  retardation  of  the  blood  is  to 
be  traced  in  the  structure  of  the  arterial  system  itself.  The  velo- 
city of  a  fluid  passing  through  a  tube  of  unequal  diameter  in 
different  parts,  must  be  inversely  as  the  area  of  the  tube  at  each 
respective  point  of  its  length ;  that  is,  invei'sely  as  the  square  of 
the  diameter."  Accordingly,  if  we  suppose  two  cyhnders  of  dif- 
ferent diameters  joined  together,  and  that  a  fluid  is  passing  from 
one  end  to  the  other,  it  must  evidently  move  with  less  velocity 
in  the  wider  than  in  the  narrower  part ;  for  if  it  did  not,  it  would 
leave  behind  it  a  vacant  space.  But  a  vacuum  of  this  kind  can 
never  take  place  in  the  living  body,  in  which,  with  whatever 
properties  they  may  be  endowed,  the  fluids  are  still  obedient  to 
the  laws  of  hydraulics.  The  arterial  system  consists  of  an  assem- 
blage of  tubes,  which,  though  they  continually  diminish  in  their 
diameter  as  they  divide  into  branches,  yet  as  the  united  area  of 
of  the  branches  is  always  greater  than  that  of  the  trunk  out  of 
which  they  arose,  they  constitute,  when  taken  as  a  whole,  a  sys- 

*  [See  section  450,  note  *] 
18 


206  NUTRITIVE    FUNCTIONS. 

tern  of  channels  of  continually  increasing  capacity,  as  we  fol- 
low them  from  the  heart  to  the  extremities.  The  whole  cavity 
through  which  the  blood  moves,  may  therefore  be  represented 
by  a  cone,  having  its  apex  at  the  heart,  and  its  base  at  the  ter- 
mination of  the  minutest  arterial  ramifications.  The  beginning 
of  the  aorta  is,  in  reality,  the  narrowest  part  of  the  whole  channel, 
considered  with  reference  to  the  united  areas  of  the  successive 
orders  of  branches  as  they  divide.  The  sum  of  all  the  areas  of 
the  minutest  ramifications  of  the  arteries  existing  in  the  body, 
comprising  myriads  of  myriads  of  vessels,  if  they  could  be  col- 
lected together,  would  form  an  area  of  immense  extent.  No 
wonder,  therefore,  that  the  motion  of  the  blood,  when  it  arrives 
at  this  part  of  the  circulation,  should  be  so  prodigiously  retarded 
as  actual  observation  shows  us  that  it  is. 

460.  Notwithstanding  this  great  difference  in  the  velocity  of 
the  blood  in  diflJerent  parts  of  its  arterial  circulation,  it  would 
appear  from  the  experiments  of  Poiseuille,  that  the  pressure 
exerted  by  the  blood,  as  measured  by  the  column  of  mercury  it 
will  support  at  different  distances  from  the  heart,  is  not  very 
different. 

461.  The  arteries  being  always  full  of  blood,  and  their  coats 
distended  by  its  pres-ence,  the  elasticity  of  these  coats  is  always 
exerted,  and  produces  a  constant  pressure  on  the  blood,  inde- 
pendently of  any  force  that  may  urge  it  forwards.  The  entry  of 
a  fresh  quantity  of  blood  forced  into  them  by  the  action  of  the 
heart,  produces  a  slight  additional  distention  of  their  coats,  and 
a  consequent  reaction  of  their  elasticity.  This  reaction  of  the 
arteries  in  each  interval  of  the  heart's  pulsation,  tends  much  to 
equalize  the  motion  of  the  blood ;  and  has  the  effect  also  of  pro- 
pagating the  impulse  originally  given  to  it  by  the  heart  very 
quickly  to  the  remoter  parts  of  the  arterial  system.  The  velocity 
with  which  this  impulse  is  transmitted,  is  much  greater  than  the 
actual  motion  of  the  blood,  and  partakes  of  the^nature  of  a  wave, 
which,  as  is  well  known,  advances  with  incomparably  greater 
rapidity  than  the  progressive  motion  of  the  fluid  itself.  It  is  the 
impulse  given  to  the  sides  of  the  artery  by  this  wave,  as  it  may 
be  called,  which  constitutes  the  pulse,  and  which  is  more  par- 
ticularly rendered  sensible  on  compressing  the  artery  with  the 
finsjer. 

462.  It  has  been  a  much  disputed  question,  both  here  and  on 
the  continent,  whether  the  arteries  assist  the  circulation  by  ex- 
erting any  contractile  power  of  their  own.  The  evidence  in 
favour  of  their  exerting  such  an  action  is  very  strong,  and  ap- 
parently irresistible.  The  power  of  the  heart,  however  enormous 
we  may  suppose  it  to  be,  would  appear  to  be  quite  inadequate  to 
drive  the  whole  mass  of  the  blood  through  the  infinite  number  of 
narrow  and  contorted  channels  through  which  it  actually  moves, 


POWERS    CONCERNED    IN    THE    CIRCULATION.  207 

were  it  not  assisted  by  some  additional  force,  derived  from  the 
contractions  of  the  arteries  themselves.  Many  facts  prove  that 
variations  in  the  impetus  of  the  blood,  and  in  the  quantity  which 
circulates  in  particular  parts,  occur  at  different  times,  quite  inde- 
pendently of  any  general  alteration  of  the  circulation,  or  of  any 
corresponding  change  in  the  action  of  the  heart.  The  only  as- 
signable cause  for  such  differences  is  a  variation  in  the  extent  of 
action  of  the  arteries.  Numerous  experiments  show  that  stimuli 
applied  to  the  smaller  arteries  occasion  in  them  a  temporary 
constriction  at  the  points  where  irritation  has  been  excited ; 
which,  after  a  certain  time,  goes  off  spontaneously.  Various 
■other  facts  also  prove  that  the  arteries  have  a  power  of  spon- 
taneous contraction;  this  power  is  exhibited  in  the  most  unequi- 
vocal manner  when  an  artery  has  been  cut  across;  the  consequent 
hemorrhage  being,  after  some  time,  stopped  by  the  action  of  the 
coats  of  the  artery.  This  contractile  force  of  arteries  is  probably 
deriv^ed  from  muscularity,  although  the  muscular  structure  is  not 
distinctly  perceptible.  It  is  considerably  greater  in  the  smaller 
than  in  the  larger  arteries;  and  it  is  probably  greatest  of  all  in 
the  capillaries. 

463.  Notwithstanding  the  facts  above  stated,  the  muscularity 
of  the  arteries  is  denied  by  some  of  the  most  eminent  of  the  con- 
tinental physiologists ;  and  among  others,  Magendie,  Broussais, 
Adelon,  Alard,  Rolando,  and  Muller.* 

3.  Action  of  the  Capillaries. 

464.  The  particular  agents  by  which  the  circulation  is  carried 
on  in  the  capillary  vessels  cannot  be  very  precisely  determined ; 
and  the  subject  has  given  rise  to  much  controversy  among  phy- 
siologists. The  action  of  these  vessels  is  evidently  of  the  greatest 
importance  in  relation  to  every  other  function,  and  more  espe- 
cially to  the  production  of  every  permanent  change  which  may 
take  place  in  the  form  or  composition  of  the  organs.  The  vari- 
able state  of  the  circulation  in  different  organs  at  different  times, 
must  be  occasioned  principally  by  diversities  in  the  actions  of  the 
capillaries.  It  appears  from  the  experiments  of  Hunter,  that 
while  the  larger  arteries  possess  a  greater  proportion  of  elastic 
power,  the  saialler  arteries  have  a  comparatively  greater  muscu- 
lar contractility;  and  this  reasoning  may,  with  great  appearance 
of  probability,  be  extended  to  the  capillaries.  It  would  appear, 
indeed,  from  various  observations  on  the  inferior  animals,  and  in 
particular  from  those  made  by  Dr.  W.  Philip,  that  the  circula- 
tion in  the  capillaries  may  be  kept  up  for  some  time  after  the 

*  See  Milligan's  Translation  of  Magendie,  and  Bostock's  Pliysiology, 
p.  344r.     [Also,  Dunglison,  Op.  cit.  ii.  170.] 


208  '  NUTRITIVE    rUNCTIONS. 

pulsation  of  the  heart  has  entirely  ceased,  and  even  when  that 
organ  has  been  altogether  removed  from  the  body.  In  many 
cases,  indeed,  the  capillaries,  when  viewed  with  the  microscope, 
have  been  seen  to  contract  on  the  application  to  them  of  stimuli, 
which,  in  other  cases,  excite  contractions  in  the  muscular  fibre. 
The  pulsatory  motion  of  the  blood  given  to  it  in  the  arteries  by 
the  periodical  contractions  of  the  heart,  is  scarcely  sensible  in 
the  smaller  arteries,  and  is  totally  lost  in  the  capillaries,  where 
we  find  the  blood  moving  in  a  uniform  stream.  This  is  a  ne- 
cessary consequence  of  the  tortuous  course  of  the  channels 
through  which  it  passes,  and  of  the  numerous  communications 
among  these  vessels,  which  equalize  the  ejEfects  of  the  original- 
impulse,  and  extend  them  over  the  whole  period  of  time  that 
intervenes  between  one  pulsation  and  the  next.* 

4.  Action  of  the  Veins. 

465.  The  blood  which  is  returned  from  every  part  of  the  sys- 
tem by  the  veins,  is  gradually  accelerated  in  its  progress  towards 
the  heart,  for  a  similar  reason  that  it  was  retarded  in  its  trans- 
mission through  the  arteries,  namely,  that  the  capacity  of  the 
channel  through  which  this  fluid  is  passing  is  continually  diminish- 
ing; for  the  united  area  of  the  beginnings  of  the  veins  is  incom- 
parably smaller  than  the  conjoined  area  of  the  two  vense  cavag. 
The  office  of  the  veins  generally  appears,  on  the  whole,  to  par- 
take more  of  a  mechanical  action  than  that  of  the  arteries,  though 
it  is  probable  that  the  smaller  veins  may  derive  from  their  struc- 
ture powers  analogous  to  those  of  the  capillaries.  The  power 
which  impels  the  blood  forwards  in  the  veins  is  chiefly  the 
impulse  it  has  already  received,  and  the  pressure  exerted  on  it 
from  behind,  or  what  has  been  technically  termed  the  vis  ti  tergo. 
This  force  is  assisted  also  in  many  situations  by  the  pressure 
made  on  the  veins  by  the  action  of  the  neighbouring  muscles, 
which,  in  consequence  of  the  valves  placed  in  the  course  of  the 
veins,  preventing  all  retrogade  motion  in  the  blood,  must  contri- 
bute to  force  it  onwards  towards  the  heart.  It  is  probable, 
however,  that  the  veins  are  not  altogether  destitute  of  a  power 
of  contraction,  though  less  considerable  than  that  possessed  by 
the  arteries  ;  and  that  the  exertion  of  this  power  has  some  share 
in  accelerating  the  motion  of  the  blood  in  the  venous  system. 
Whatever  power  may  arise  from  the  force  of  dilatation  exerted 
by  the  auricles  of  the  heart  during  their  diastole,  which,  hovi^- 

*  [The  capillaries  have  been  supposed,  by  some,  to  possess  a  vital  power  of 
expansibility  or  turg^escence ;  but  this  is  probably  owing  to  the  afflux  ofblood  to 
an  irritated  part.  The  erectile  tissues  become  turgid,  but  not  until  excitation 
is  induced,  directly  or  indirectly,  in  the  nerves  of  the  parts,  and  this  is  probably 
the  case  with  the  capillary  or  intermediate  vessels.] 


POWERS    CONCERNED    IN    THE    CIRCULATION.  209 

ever,  we  have  reason  to  believe  is  very  trifling,  naust  be  added  to 
the  account  of  the  forces  that  tend  to  promote  the  motion  of  the 
blood  towards  tliose  cavities.  Some  have  supposed  that  a  similar 
power  is  derived  from  the  expansion  of  the  chest  in  the  act  of 
inspiration  ;  but  this,  if  it  exist  at  all,  is  of  very  inconsiderable 
amount.  The  vena3  cavae  near  their  termination  in  the  auricles, 
are  furnished  with  a  distinct  layer  of  muscular  fibres,  apparently 
for  the  purpose  of  enabling  them  to  resist  the  retrograde  impulse 
communicated  to  the  blood  by  the  contraction  of  the  auricles.* 

5.  Pulmonary  Circulation. 

466.  There  is  nothing  very  different  in  the  circulation  through 
the  pulmonary  arteries,  capillaries,  and  veins,  from  what  takes 
place  in  the  corresponding  vessels  of  the  systemic  circulation 
excepting  that  junctions  are  occasionally  formed  between  the 
smaller  branches  of  the  bronchial  arteries  which  have  their  origin 
from  the  aorta  and  the  pulmonary  artery.  The  phenomena 
"which  occur  in  asphyxia,  or  death  from  suffocation,  prove  that 
the  pulmonary  capillaries  have  a  distinct  action  of  their  own  in 
carrying  on  the  circulation.  The  beautiful  net-work  formed  by 
the  inosculating  branches  of  the  pulmonary  capillaries  was  first 
observed  by  Malpighi,  and  has  received  the  name  of  Rete  mira- 
hile  Malpighi.  The  pulmonary  veins  are  wholly  destitute  of 
valves,  not  being  exposed  to  variations  of  pressure  from  the  ac- 
tions of  the  surrounding  muscles.  They  are  furnished,  like  the 
venae  cavae,  with  a  reinforcement  of  muscular  fibres,  in  the  neigh- 
bourhood of  the  left  auricle  in  which  they  terminate. 

467.  In  one  respect,  the  vessels  of  the  pulmonary  circulation 
differ  from  those  of  the  sysremic,  namely,  that  the  arteries  are 
carrying  dark-coloured  blood,  and  the  veins  florid  blood ;  the 
former  being  termed  venous,  from  having  the  qualities  of  that 
which  is  returned  by  the  veins  of  the  system ;  the  latter  being 
termed  arterial,  because  it  has  the  qualities  of  that  which  circu- 
lates in  the  systemic  arteries. 

*  [The  same  alternate  contraction  and  dilatation  has  been  observed  in  the 
venae  cavse  after  the  heart  was  removed  from  the  body  as  in  the  heart  itself, 
Dunglison's  Physiology,  3d  edit.  ii.  181,  and  Dr.  J.  J.  Allison,  in  Amer. 
Journ.  of  the  Med.  Sciences,  Feb.  1839. 

In  addition  to  the  powers  already  mentioned  as  concerned  in  the  circu- 
lation, it  has  been  maintained  by  many,  that  the  blood  possesses  a  power  of 
automatic  or  self  motion,  either  in  consequence  of  its  own  vital  properties,  or 
of  some  electroid  agency  derived  from  the  vessels  in  which  it  circulates  ;  but 
granting  that  such  may  be  the  fact, — as  in  the  embryo,  in  which  blood  in 
motion  can  be  detected  before  vessels  are  in  esse, — it  can  exert  but  little 
influence  on  the  circulation.] 

18* 


210  NUTRITIVE    FUNCTIONS. 


CHAPTER   IX. 


RESPIRATION. 

468.  The  object  of  the  function  of  respiration  js  the  conversion 

of  venous  into  arterial  blood,  by  its  exposure  to  the  chemical 
influence  of  atmospheric  air  received  into  the  lungs.  This  ar- 
terialization  of  the  blood  is  a  process  more  essential  to  the  con- 
tinuance of  Hfe  than  even  the  assimilation  of  aliment.  The 
necessity  for  air  is  more  imperious  than  the  demand  for  food ; 
and  the  interruption  to  its  supply  cannot  be  continued  for  a  few 
minutes  without  being  fatal  to  life.  In  comparing  the  extent  to 
which  this  function  ''  is  carried  on  in  the  different  classes  of 
animals,  we  shall  find  that  in  general  the  intensity  of  all  the  vital 
actions  is  nearly  in  proportion  to  the  perfection  in  which  the 
objects  of  this  function  are  accomplished. 

469.  The  consideration  of  the  function  of  respiration,  then, 
comprises  an  inquiry  into  the  three  following  objects  ;  first,  the 
mechanical  means  by  which  the  air  is  alternately  admitted  and 
discharged  from  the  lungs  ;  secondly,  the  provision  made  for 
bringing  the  blood  to  the  lungs,  and  exposing  it  to  the  action  of 
the  air ;  and,  lastly,  the  chemical  changes  which  are  produced 
on  the  blood  by  the  action  of  the  air  in  that  organs  The  means 
of  fulfilling  the  second  of  these  objects  has  already  been  suffi- 
ciently explained  in  the  account  we  haye  just  given  of  the  cir- 
culation. It  remains,  therefore,  that  we  consider  the  first  and 
tiiird  branches  of  the  inquiry. 


Sect.  I. — Mechanism  of  Respiration. 

470.  The  anatomical  structure  of  the  organs  of  respiration, 
namely,  the  lungs  with  the  air  pr.ssages,  including  the  trachea, 
bronchia,  and  air  cells,  together  with  the  general  conical  cavity 
of  the  thoi'ax,  bounded  by  the  sternum  in  front,  the  spine  behind,' 
and  the  ribs  on  every  other  side,  while  its  lower  side,  or  basis  of 
the  cone,  is  closed  by  the  diaphragm,  are  subjects  of  anatomical 
inquiry. 

471.  The  mechanical  act  of  respiration  is  divisible  into  two 
periods,  that  of  inspiration,  during  which  air  is  drawn  into  the 
lungs,  so  as  to  distend  their  vesicles,  and  expiration,  during  which 
the  air  which  had  been  so.received  is  expelled. 

472.  Inspiration  is  accomplished  by  enlarging  the  capacity  of 


MECHANISM    OF    RESPIRATION.  211 

the  thorax  in  all  its  dimensions.  This  is  eflected  by  the  action  of 
different  sets  of  muscles.  The  principal  muscle  of  inspiration  is 
the  diaphragm,  which  has  an  arched  form,  the  convexity  being 
towards  the  chest.  Its  attachments,  by  radiating  fibres  arising 
from  a  central  tendinous  portion,  and  inserted  into  the  ribs 
which  form  the  lower  margin  of  the  chest,  are  such,  that  when 
they  contract  they  draw  down  the  middle  tendon,  and  render  the 
diaphragm  more  f^at  than  it  was  before.  Hence  the  space  above 
is  enlarged.  The  flattening  of  the  diaphragm  takes  place  chiefly 
in  the  fieshy  lateral  portions,  but  the  middle  tendon  is  also  slightly 
depressed. 

473.  The  second  set  of  muscles  employed  in  inspiration  are 
those  which  elevate  the  ribs ;  and  the  principal  of  these  are  the 
two  layers  of  intercostal  muscles.  Each  rib  is  capable  of  a  small 
degree  of  motion  on  the  extremity  by  which  it  is  articulated 
with  the  vertebrae.  This  motion  is  chiefly  an  upward  and  a 
downward  motion.  But  since  the  ribs,  as  they  advance  from  the 
spine  towards  the  sternum,  bend  downwards  in  their  course,  the 
effect  of  the  vertical  motion  just  described  will  be  that  of  raising 
the  sternum,  and  increasing  its  distance  from  the  spine ;  enlarg- 
ing, consequently,  the  capacity  of  the  chest.  The  intercostal 
muscles  are  disposed  in  two  layers,  each  passing  obliquely,  but 
with  opposite  inclinations,  from  one  rib  to  the  adjacent  rib. 
Hence  they  act  with  the  advantage  of  oblique  muscles  on  the 
principles  formerly  explained. 

474.  Thus  there  are  two  ways  in  which  the  chest  may  be 
dilated  ;  first,  by  the  diaphragm,  and,  secondly,  by  the  muscles 
which  elevate  the  ribs.  In  general,  when  the  respiration  is 
natural  and  unconstrained,  we  chiefly  breathe  by  means  of  the 
diaphragm  ;  but  we  also  employ  the  intercostal  muscles  when 
the  respiration  is  quickened  or  impeded  by  any  cause.  If  respi- 
ration should  be  rendered  difficult  several  other  muscles  are 
called  into  play  in  aid  of  the  intercostals  ;  namely,  the  great 
muscles  situate  in  the  back  and  sides,  which  connect  the  ribs  to 
the  spine  and  to  the  scapula ;  and  several  of  the  muscles  of  the 
neck  are  also  thrown  into  action  as  auxiliaries  on  these  occasions, 
when  the  respiration  becomes  laborious. 

475.  The  glottis  is  kept  open,  during  inspiration,  by  the  muscles 
of  the  larynx  which  perform  that  office  ;  and  when  a  foixible 
inspiration  is  made,  the  nostrils  are  expanded,  the  lower  jaw 
depressed,  and  every  action,  which  can  in  the  remotest  degree 
concur  in  the  effect  of  removing  all  obstruction  to  the  passage 
of  the  air  into  the  trachea,  is  exerted. 

476.  Having  thus  shown  how  the  cavity  of  the  thorax  is 
dilated,  let  us  next  trace  the  effect  of  this  expansion  upon  the 
lungs.  It  is  obvious,  that  if  when,  by  the  descent  of  the  diaphragm 
and  elevation  of  the  ribs,  the  cavity  of  the  chest  is  enlarged,  the 


212  NUTRITIVE    FUNCTIONS. 

lungs  were  to  remain  in  their  original  situation,  an  empty 
space  would  be  left  between  them  and  the  sides  of  the  chest.  But 
no  vacuum  can  ever  take  place  in  the  living  body ;  the  air  already 
present  in  the  air-cells  of  the  lungs  must,  by  its  elasticity,  expand 
these  organs ;  and  the  external  air,  having  access  to  them  by 
means  of  the  trachea,  will  rush  in  through  that  tube  in  order  to 
restore  the  equilibrium.     This,  then,  is  inspiration. 

477.  The  expulsion  of  the  air  from  the  lungs  constitutes  expi- 
ration. This  takes  place  as  soon  as  the  air  which  had  been  in- 
spired has  lost  a  certain  portion  of  its  oxygen,  and  received  in 
return  a  certain  quantity  of  carbonic  acid  gas  and  of  watery  vapour, 
by  having  had  communication  with  the  blood  in  the  pulmonary 
capillaries.  When  thus  contaminated  it  excites  an  uneasy  sensa- 
tion in  the  chest,  and  the  intercostal  muscles  relaxing,  the  ribs 
fall  into  their  original  situation,  and  the  relaxed  diaphragm  is 
pushed  upwards  by  the  action  of  the  abdominal  muscles.  The 
lungs,  being  compressed,  expel  the  air  they  had  received,  and 
this  air  escapes  through  the  trachea.  The  movements  of  inspir- 
ation are  in  like  manner  prompted  by  an  uneasy  sensation  con- 
sequent upon  the  presence  of  venous  blood  in  the  pulmonary 
system. 

478.  Thus  the  lungs  are  merely  passive  agents  in  the  me- 
chanism of  respiration ;  for  it  does  not  appear  that  they  have, 
as  was  at  one  time  supposed,  any  inherent  power  of  extension  or 
contraction,  if  we  except  only  that  arising  from  the  elasticity 
which  they  possess  in  common  with  all  membranous  textures. 
Hence,  if  an  opening  be  made  in  the  sides  of  the  chest,  the  lung 
on  that  side  immediately  collapses,  in  consequence  of  the  inter- 
nal pressure  of  the  air  against  its  air-cells,  which  kept  the  lung 
expanded,  being  balanced  by  the  external  pressure  of  the  atmos- 
phere which  has  been  admitted  on  the  outer  surface  of  the  lung. 

479.  The  alternations  of  inspiration  and  expiration,  which 
together  constitute  one  act  of  breathing,  take  place,  in  ordinary 
health,  about  once  for  every  four  pulsations  of  the  heart;  and  as 
both  are  generally  accelerated  in  the  same  proportion,  the  same 
rule  usually  holds  good  in  states  of  disease.* 

480.  The  quantity  of  air  taken  into  the  lungs  at  each  inspira- 
tion has  been  very  variously  estimated  by  different  experi- 
mentalists. It  differs,  indeed,  considerably  in  different  persons, 
and  in  different  states  of  the  system  ;  but  from  the  concurrent 
testimony  of  the  most  accurate  experimentalists,  the  average 
quantity  appears  to  be  about  forty  cubic  inches.  By  a  forcible 
expiration  there  may  be  expelled,  in  addition  to  this  quantity, 
about  a  hundred  and  seventy  inches  more.     But  even  after  this 

*  [The  number  of  expirations  or  inspirations,  in  a  given  time,  varies. 
The  average  may  be  estimated  at  about  18  per  minute.] 


CHEMICAL    EFFECTS    OF    RESPIRATION.  213 

effort  has  been  made,  there  still  remain  about  a  hundred  and 
twenty  cubic  inches  in  the  lungs  ;  so  that,  adding  all  these  quanti- 
ties together,  it  will  appear  that  the  lungs  are  capable  of  contain- 
ing, while  in  their  most  expanded  state,  after  ordinary  inspiration, 
about  three  hundred  and  thirty  cubic  inches  of  air.  One-eighth 
of  the  whole  contents  of  the  lungs,  therefore,  is  changed  at  each 
respiration.  If  we  suppose  that  we  respire  twenty  times  each 
minute,  the  quantity  of  air  respired  during  twenty-four  hours 
will  amount  to  six  hundred  and  sixty-six  cubic  feet.* 

Sect.  II. — Chemical  Effects  of  Respiration. 

481.  Before  we  inquire  into  the  changes  produced  on  the  blood 
by  its  exposure  to  the  air  in  the  lungs,  it  will  be  proper  to  notice 
the  changes  which  the  air  undergoes  by  this  process.  The  air 
of  the  atmosphere  is  found  by  chemical  analysis  to  consist  of 
seventy-nine  per  cent,  of  nitrogen,  twenty  of  oxygen,  and  one  of 
carbonic  acid.f  When  expired,  the  principal  change  which  has 
taken  place  in  it  is  the  substitution  of  a  certain  quantity,  which, 
on  an  average,  is  about  seven  and  a  half  per  cent,  of  carbonic 
acid  gas  for  a  nearly  equal  quantity  of  oxygen  gas,  and  the  addi- 
tion of  a  quantity  of  aqueous  vapour.  Air  which  has  passed 
through  the  lungs  only  once  is  incapable  of  supporting  the  com- 
bustion of  a  taper,  which  is  accordingly  extinguished  the  moment 
it  is  immersed  in  the  air.  The  weight  of  the  oxygen  consumed 
in  the  air  respired  in  the  course  of  a  day,  will  be  found  to 
amount  to  about  two  pounds  and  a  quarter  avoirdupois,  or  nearly 
15,500  grains,  occupying  in  its  gaseous  state  a  volume  of  45,000 
cubic  [inches,  or  a  little  more  than  twenty-six  cubic  feet.  The 
quantity  of  carbonic  acid  expelled  from  the  lungs  is  somewhat 
less  ttian  this;  its  total  bulk  in  the  twenty-four  hours  amounting 
on  an  average  only  to  40,000  cubic  inches,  or  23-2  cubic  feet. 
Its  total  weight  is  18,600  grains,  or  2-86  pounds  avoirdupois. 
The  weight  of  the  quantity  of  carbon  contained  in  this  amount 
of  carbonic  acid  is  5,208  grains,  or  very  nearly  three  quarters  of 
a  pound  ;  and  that  of  the  quantity  of  oxygen  is  13,392  grains. 
Hence  the  quantity  of  oxygen  which  disappears  from  the  air 
respired,  over  and  above  that  which  enters  into  the  composition 
of  the  carbonic  acid  gas,  is  2,108  grains,  and  had  occupied,  while 
in  a  gaseous  state,  5000  cubic  inches.  The  only  way  in  which 
we  account  for  the  disappearance  of  this  oxygen  is,  by  supposing 
it  to  have  been  absorbed  by  the  blood. 

*  See  Bostock  on  Respiration,  and  also  his  Physiology,  3d  edition,  pages 
321  and  361. 

f  The  recent  experiments  of  De  Saussure  tend  to  show  that  the  propor- 
tional quantity  of  carbonic  acid  gas  in  atmospheric  air  is  even  less  than  this. 
He  estimates  it  at  only  four  parts  by  volume  in  a  million  volumes  of  air. 


214  NUTRITIVE    FUNCTIONS. 

482.  The  numbers  given  above  are,  of  course,  to  be  taken  as 
imperfect  approximations  to  the  truth,  being  deduced  as  the  mean 
of  the  best  authenticated  observations,  in  which,  however,  there 
exist  such  great  discrepancies  as  to  render  any  accurate  appre- 
ciations nearly  hopeless.  An  excellent  summary  of  the  results 
which  have  been  arrived  at  by  different  experimentalists,  with 
critical  remarks  on  their  respective  values,  will  be  found  in  Dr. 
Rostock's  Elementary  System  of  Physiology.* 

483.  Much  difference  of  opinion  has  prevailed  with  respect  to 
the  absorption  or  evolution  of  nitrogen  during  respiration.  From 
the  accurate  experiments  on  this  subject  made  by  Dr.  Edwards, 
it  appears  that  on  some  occasions  there  is  a  small  increase,  and 
in  others  a  diminution  of  the  nitrogen  of  the  air  respired.  But 
the  limits  within  which  we  must  confine  ourselves  in  this  treatise, 
forbid  our  entering  into  the  experimental  details  from  which  this 
conclusion  is  deduced. 

484.  The  quantity  of  water  exhaled  from  the  lungs  in  the 
course  of  a  day,  has  been  estimated  by  Dr.  Thomson  at  nineteen 
ounces,  and  by  Dr.  Dalton  at  twenty-four. 

485.  It  should  be  observed,  that  the  quantity  of  carbonic  acid 
thrown  off  from  the  lungs,  is  liable  to  great  variation  from  several 
causes ;  it  has  been  found  by  Dr.  Prout  to  be  greatest  at  noon, 
and  least  at  midnight.  It  has  also  been  ascertained  that  it  is  less 
in  youth  than  in  middle  age  ;  and  that  it  is  diminished  by  causes 
which  induce  fatigue  or  lessen  the  vital  energies. 

486.  We  have  next  to  inquire  what  changes  have,  in  the  mean- 
while, been  effected  in  the  blood  by  the  action  of  the  air  to  which 
it  has  been  subjected  in  the  lungs.  A  visible  alteration  in  the 
first  place,  is  produced  in  its  colour,  which,  from  being  of  a  dark 
purple,  nearly  approaching  to  black,  when  it  arrives  at  the  air 
cells  by  the  pulmonary  arteries,  has  acquired  the  bright  intensely 
scarlet  hue  of  arterial  blood,  when  brought  back  to  the  heart  by 
the  pulmonary  veins.  In  other  respects,  however,  its  sensible 
qualities  do  not  appear  to  have  undergone  any  material  change. 
Judging  from  the  changes  produced  on  the  air,  which  has  been 
in  contact  with  it,  we  are  warranted  in  the  inference  that  it  has 
parted  with  a  certain  quantity  of  carbonic  acid  and  of  water, 
and  that  it  has  in  return  acquired  a  certain  proportion  of  oxygen. 
Since  it  has  been  found  that  the  quantity  of  oxygen  absorbed,  is 
greater  than  that  which  enters  into  the  composition  of  the  car- 
bonic acid  evolved,  it  is  obvious  that  at  least  the  excess  of  oxygen 
is  directly  absorbed  by  the  blood ;  and  this  absorption,  constitutes, 
no  doubt,  an  essential  part  of  its  arterialization. 

.  487.    It  has  been  much  disputed  whether   the  combination 

*|We  refer  particularly  to  the  3d  section  of  chap.  vli.  p.  336-362.     [See, 
Iso,  on  the  whole  of  this  subject,  Dunglison's  Physiology,  3d  edit.  ii.  99.] 


CHEMICAL    EFFECTS    OF    RESPIRATION.  •  215 

"which  seems  to  be  effected  between  the  oxygen  of  the  air  and  the 
carbon  furnished  by  the  blood,  occurs  during  the  act  of  respira- 
tion, and  takes  place  in  the  air  cells  of  the  lungs,  or  whether  it 
takes  place  in  the  course  of  circulation.  On  the  first  hypothesis, 
the  chemical  process  would  be  very  analogous  to  the  simple 
combustion  of  charcoal,  which  may  be  conceived  to  be  contained 
in  the  venous  blood  in  a  free  state,  exceedingly  divided  and  ready 
to  combine  with  the  oxygen  of  the  air;  and  imparting  to  that 
venous  blood  its  characteristic  dark  colour;  while  arterial  blood, 
from  which  the  carbon  had  been  eliminated,  would  exhibit  the 
red  colour  natural  to  blood.  On  the  second  hypothesis,  we  must 
suppose  that  the  whole  of  the  oxygen,  which  disappears  from  the 
air  respired,  is  absorbed  by  the  blood  in  the  pulmonary  capilla- 
ries, and  passes  on  with  it  into  the  systemic  circulation.  The 
blood  becoming  venous  in  the  course  of  the  circulation,  by  the  dif- 
ferent processes  to  which  it  is  subjected  for  supplying  the  organs 
with  the  materials  required  in  the  exercise  of  their  respective 
functions,  the  proportion  of  carbon  which  it  contains  is  increased, 
both  by  the  abstraction  of  the  other  elements,  and  by  the  addition 
of  nutritive  materials  prepared  by  the  organs  of  digestion.  The 
oxygen,  which  had  been  absorbed  by  the  blood  in  the  lungs,  now 
combines  with  the  redundant  carbon,  and  forms  with  it  either 
oxide  of  carbon,  or  carbonic  acid,  which  is  exhaled  during  a 
subsequent  exposure  to  the  air  in  the  lungs.  Many  facts  tend 
strongly  to  confirm  our  belief  in  the  latter  of  these  hypotheses.* 
488.  It  appears  from  a  multitude  of  experiments,  as  well  as 
from  observations  of  the  phenomena  which  take  place  in  asphyxia, 
(that  is,  in  the  suspension  of  the  vital  actions  from  an  interrup- 
tion to  respiration,  as  in  hanging  or  drowning,  or  immersion  in 
any  gas  not  fitted  for  respiration,)  that  if  the  blood  be  not  arte- 
rialized,  and  if,  retaining  its  venous  character,  it  be  circulated  in 
that  state  through  the  arteries  of  the  system,  it  will  act  as  a 
poison  to  the  organs  to  which  it  is  sent,  destroying  both  the 
nervous  and  sensorial  powers,  and  impairing  the  irritability  of 
the  muscles  ;  and  that  this  is  the  cause  of  the  rapidity  with  which 

*  [The  knowledge  we  have  attained,  of  late  years,  on  the  transmission  of 
gases  through  animal  membranes,  aids  us  materially  in  the  solution  of  this 
interesting  question.  The  rate  of  transmission  of  carbonic  acid  is  greater  than 
that  of  nitrogen.  We  can  hence  understand,  that  more  oxygen  than  azote 
may  pass  through  the  coats  of  the  pulmonary  blood-vessels,  and  can  compre- 
hend the  facility  with  which  the  carbonic  acid,  formed,  as  we  conceive,  in  the 
course  of  the  circulation,  permeates  the  same  vessels,  and  mixes,  by  diffusion, 
with  the  air  in  the  lungs.  Miiller  considers,  that  the  air  passes  into  the  blood- 
vessels of  the  lungs,  where  he  thinks  it  is  decomposed,  owing  to  the  affinity 
of  oxygen  for  the  red  particles  of  the  blood;  carbonic  acid  being  formed, 
which  is  exhaled  in  the  gaseous  form,  along  with  the  greater  part  of  the 
'  nitrogen.] 


216  NUTRITIVE    FUNCTIONS. 

death  ensues  under  these  circumstances.*  It  thus  appears  that 
respiration  requires  to  be  constantly  kept  up  in  order  to  free  the 
blood  from  the  continual  additions  of  carbon  which  are  made  to 
it  by  the  various  processes  of  assimilation  and  absorption.  It  is 
also  a  principal  agent  in  perfecting  the  animahzation  of  the  chyle, 
which  is  added  to  the  blood,  and  in  converting  it  into  fibrin. 


Sect.  III. — Animal  Temperature. 

489.  Since  we  find  that  the  human  body,  as  well  as  those  of 
all  warm-blooded  animals,  is  constantly  maintained  during  life  at 
a  temperature  higher  than  that  of  the  surrounding  medium,  at 
least  in  temperate  cUmates,  it  becomes  interesting  to  inquire  into 
the  sources  whence  this  heat  is  evolved.  The  union  of  carbon 
and  oxygen,  which  takes  place  in  consequence  of  respiration,  is 
the  most  obvious  of  these  sources  ;  and  suggests  that  the  evolu- 
tion of  animal  heat  takes  place  in  a  manner  somewhat  analogous 
to  the  ordinary  combustion  of  carbonaceous  fuel.  The  circum- 
stance of  the  equable  heat  of  every  part  of  the  body,  excepting 
the  immediate  surface  where  it  is  cooled  by  the,  contact  bf  the 
air,  and  by  cutaneous  perspiration,  would  be  in  perfect  accord- 
ance with  the  theory  of  Dr.  Crawford  already  explained ;  for  if 
the  combination  of  oxygen  with  carbon  take  place  gradually  in 
the  course  of  the  circulation,  it  will  follow  that  the  evolution  of 
heat  will  also  take  place  at  the  same  time,  and  in  the  vessels 
employed  in  the  circulation.  Or  even  if  the  combination  took 
place  in  the  lungs,  if  it  could  be  shown,  as  Dr.  Crawford  endea- 
voured to  prove,  that  arterial  blood  has  a  greater  capacity  for 
caloric  than  venous  blood,  all  the  heat  that  would  have  been 
.evolved  in  the    pulmonary  vessels  would   be  absorbed    by  the 

arterial  blood,  and  given  out  in  the  course  of  its  circulation, 
during  its  gradual  conversion  into  venous  blood,  which  has  a  less 
capacity  for  caloric. 

490.  It  would,  appear,  however,  from  some  recent  experiments 
of  Dulong  and  Despretz,f  that  only  three-fourths  of  the  whole 

*  [This  was  the  view  of  Bichat,  but  there  are  numerous  difficulties  in  the 
way  of  its  adoption.  The  experiments  of  Williams  (Edinburg  Med.  and 
Surgical  Journal,  Ixxvii.  1823,)  and  of  Kay  (Ibid.  xxix.  and  the  Physiology 
and  Pathology,  &c.  of  Asphyxia,  Lond.  1834.)  have  shown,  that  the  inter- 
ruption is  owing  to  the  nonconversion  of  venous  into  arterial  blood,  and  to  the 
non-adaptation  of  the  radicles  of  the  pulmonary  veins  for  anything  but  arterial 
blood ;  owing  to  which  causes,  stagnation  of  blood  supervenes  in  the  pulmo- 
nary radicles,  and  the  passage  of  the  blood  from  the  right  to  the  left  side  of 
the  heart  is  prevented.  Art.  Asphyxia,  in  Amer.  Cyclopedia  of  Practical 
Medicine  and  Surgery,  Part  X.  Philadelphia,  1836  ;  and  Dr.  W.  P.  Allison,  in 
Edin.  Med.  and  Surgical  Journal,  Jan.  1836.] 

t  See  Miiller's  Physiology,  by  Baly,  p.  83. 


SECRETION. 


217 


quantity  of  caloric  produced  by  the  living  system  can  be  explained 
by  the  combination  of  oxygen  with  carbon  in  respiration.  Proba- 
bly, therefore,  several  of  the  other  chemical  changes  induced  on  the 
blood  by  the  processes  of  secretion  and  nutrition,  contribute  to 
the  further  evolution  of  caloric,  and  to  the  maintenance  of  the 
animal  temperature.*  This  evolution  appears,  although  primarily 
dependent  on  respiration,  to  be  in  a  great  measure  controlled  by 
the  action  of  the  nervous  powers;  and  to  be  regulated  by  a  variety 
of  circumstances  in  the  condition  of  the  other  functions,  espe- 
cially that  of  the  circulation,  which  are  very  imperfectly  known; 
and  the  inquiry  into  which  would  lead  us  into  a  field  of  discussion 
far  too  extensive  for  the  limits  within  which  we  must  confine 
ourselves  in  the  present  treatise.  We  must  content  ourselves, 
therefore,  wilh  again  referring  to  the  work  of  Dr.  Bostock  for 
more  ample  information  on  these  subjects.f 


CHAPTE 


SECRETION.  *J& 

491.  Secretion  is  that  function  by  \vhiSlT*^^?*eHS-^ubstances 
are  cither  separated  from  the  blood  or  formed  from  it,  in  order 
to  be  applied  to  some  useful  purpose  in  the  economy.  We  have 
noticed,  in  the  course  of  the  preceding  inquiries,  several  instances 
of  fluids  prepared  from  the  blood,  and  rendered  subservient  to 
different  uses  in  the  economy.  The  saliva,  the  gastric  and  pan- 
creatic juices,  the  bile,  and  the  mucus  lubricating  the  surface  of 
the  alimentary  canal,  are  all  examples  of  secretions  subservient 
to  digestion  and  assimilation. 

492.  Such  being  the  general  purpose  answered  by  this  function, 
we  have  first  to  examine  the  apparatus  provided  for  its  perform- 


*  [The  view  of  those  who  regard  the  evolution  of  caloric  to  take  place  in 
the  system  of  nutrition  over  every  part  of  the  body  appears  to  be  most  con- 
sistent with  observed  phenomena.  It  would  seem,  that  caloric  is  disengaged 
in  every  part  by  a  special  action  under  the  nervous  influence,  and  the  presence 
of  arterial  blood.  In  this  way  we  can  account  for  the  increased  heat  met 
with  in  certain  local  affections,  and  for  the  different  temperatures  of  different 
portions  of  the  body, — the  activity  of  the  function  varying  according  to  the 
organs.  It  would  not  be  easy  to  explain  this  difference  without  sup- 
posing that  each  part  has  the  power  of  disengaging  its  own  heat,  and  that 
the  conduction  of  caloric  from  one  part  to  another  is  not  sufficiently  ready  to 
prevent  the  difference  from  being  perceptible.] 

f  [See  an  elaborate  chapter  on  this  subject,  in  Dunglison's  Physiology, 
3d  edit.  ii.  238.] 

19 


218  NUTRITIVE    FUNCTIONS. 

ance ;  secondly,  the  nature  of  the  effects  obtained ;  and,  thirdly, 
the  peculiar  powers  which  are  concerned  in  their  production. 


Sect.  I. — Apparatus  for  Secretion. 

493.  The  apparatus  employed  by  nature  for  the  performance 
of  secretion  varies  considerably  in  its  structure,  in  different  in- 
stances, according  to  the  nature  of  the  product  which  is  to  result 
from  the  operation ;  and  according  as  that  product  is  merely 
separated  from  the  blood,  in  which  it  may  already  have  existed, 
oris  formed  by  the  combination  of  certain  elements  and  proximate 
principles  furnished  by  that  fluid.  In  the  simplest  cases,  where 
that  product  is  principally  aqueous,  and  apparently  consists  of 
nothing  more  than  the  serous  portion  of  the  blood  separated  from 
it  by  mere  transudation,  we  find  no  other  organs  requisite  than 
those  smooth  membranous  surfaces  which  we  have  already  des- 
cribed under  the  name  of  the  serous  membranes.  The  mucous 
secretions  proceed,  in  like  manner,  from  the  modified  yet  still 
simple  action  of  a  membranous  surface,  of  a  rather  more  refined 
structure,  namely  the  mucous  membranes.  The  more  elaborate 
products  of  secretion,  on  the  other  hand,  which  are  apparently 
formed  by  combinations  of  pre-existing  elements,  are  obtained 
by  the  agency  of  organs  of  a  more  complicated  structure,  which 
are  denominated  glands. 


Sect.  II. — Glandular  Apparatus. 

494.  The  essential  part  of  the  structure  of  a  gland  consists  in 
a  collection  of  tubes,  more  or  less  convoluted,  united  by  cellular 
substance  into  masses  of  a  rounded  form,  constituting  a  lobule. 
Each  lobule  has  a  separate  investment  of  membrane ;  and  the 
whole  aggregate  of  lobules  is  furnished  with  a  general  membra- 
nous envelope,  or  capsule.  In  every  gland  we  meet  with  a  com- 
plex arrangement  of  numerous  arteries,  veins,  nerves,  a'nd  lym- 
phatics, provided  with  ramified  excretory  ducts,  which  conduct 
away  the  secreted  matter  that  has  been  prepared  in  the  substance 
of  the  gland. 

495.  The  above  description  of  a  gland  does  not  include  those 
organs,  which,  although  resembling  the  proper  glands  in  their 
general  appearance,  perform  no  distinct  office  of  secretion,  and 
are  therefore  unprovided  with  any  excretory  duct.  This  is  the 
case  with  those  bodies  belonging  to  the  absorbent  system,  which 
bear  improperly  the  title  oi  lymphatic  or  conglobate  glands.  The 
spleen,  the  renal  capsules,  the  pineal  gland,  the  thyroid  gland, 
and  the  thymus,  are,  in  like  manner,  improperly  included  in  the 


GLANDULAR  APPARATUS.  219 

class  of  glands  ;  for  we  have  no  evidence  of  their  secreting  any 
fluid,  and  indeed  know  nothing  of  their  real  functions. 

496.  The  catalogue  of  glands,  strictly  answering  to  the  defini- 
tion, will  comprise  the  following  organs,  nanaely,  the  liver, 
pancreas,  and  kidneys ;  the  salivary,  lacrymal,  and  meibomian 
glands;  the  tonsils,  the  ceruminous  glands  of  the  ear,  and  the 
sebaceous  glands  of  the  face;  the  mammie,  the  prostate,  the  tes- 
ticle, Cowper's  glands,  the  gland ulee  odoriferas,  and  the  extensive 
system  of  mucous  glands  about  the  head  and  trunk.  These  parts, 
although  differing  widely  from  each  other  in  many  respects, 
agree  in  a  sufficient  number  of  particulars  to  allow  of  being 
classed  together  in  one  organic  system,  which  Bichat  has  termed 
the  glandular  system.* 

497.  Most  of  the  glands  are  arranged  in  pairs,  as  the  kidneys, 
testicles,  salivary  and  lacrymal  glands,  while  others  are  single, 
as  the  liver  and  the  pancreas. 

498.  The  organization  of  the  glandular  system  is  exceedingly 
complex,  and  cannot  be  unravelled  without  great  difficulty.  The 
tissue  of  which  they  are  composed  presents  us  with  no  regular 
arrangement  of  tibres,  such  as  we  see  in  the  muscles,  ligaments, 
nerves,  or  bones;  but  the  whole  structure  is  made  up  of  a  con- 
geries of  vessels  and  cells,  having  no  very  firm  cohesion  amongst 
themselves,  and  hence  admitting  very  readily  of  being  separated 
by  slight  mechanical  causes.  Whilst  organs  which  have  a  more 
extensive  fibrous  organization  possess  considerable  powers  of 
resistance,  a  very  moderate  degree  of  violence  is  sufficient  to 
tear  asunder  the  texture  of  a  gland.  The  resistance  in  the  latter 
case  is  owing  solely  to  the  cohesion  of  the  cellular  tissue  which 
connects  their  parts,  and  which  differs  in  its  density  and  strength 
in  different  glands. 

499.  There  are  three  different  ways  in  which  the  glandular 
tissue,  ov  parenchyma  of  glands,  as  it  has  been  generally  termed, 
is  disposed.  In  those  glands  which  have  been  called  conglome- 
rate, a  term  which,  as  we  have  seen,  has  been  used  in  contradis- 
tinction to  the  conglobate,  or  lymphatic  glands,  the  organ  is  made 
up  of  distinct  portions,  connected  together  by  a  large  quantity 
of  loose  cellular  tissue,  in  the  intervals  of  which  the  vessels  and 
nerves  are  situated.  These  larger  lobes  are  again  made  up  of 
smaller  lobes  united  in  the  same  way.  By  successive  divisions 
we  obtain  smaller  and  smaller  component  portions,  till  we  arrive 
at  last  at  very  small  bodies  still  visible  to  the  naked  eye,  and 

=f  [A  more  common  division  at  the  present  day  of  the  organs  of  secretion  is 
into,  1.  The  simple  exhalanl,  as  met  with  in  the  serous  membrane.  2.  The 
follicle,  in  which  there  is  a  crypt  without  any  distinct  duct,  as  in  the  tonsils, 
mucous  crypts  of  the  mucous  membranes,  sebaceouscrypts  of  the  skin,  &c.;  and, 
3.  T\\e  gland,  an  organ  of  a  solid  and  more  complex  organization,  furnished 
with  a  distinct  excretory  duct,  as  in  the  kidney,  liver,  &c.] 


220  NUTRITIVE    FUNCTIONS. 

which  are  called  by  anatomists  glandular  acini.  These  succes- 
sive lobules  are  firmer  in  proportion  as  they  are  smaller,  being 
surrounded  and  connected  with  the  adjoining  portions,  by  shorter 
and  denser  cellular  substance.  The  second,  third,  and  even  the 
fourth  subdivisions  of  these  lobes  may  easily  be  followed  with 
the  scalpel.  _The  acini  themselves  are  of  a  roundish  figure  and 
pale  colour,  and  readily  distinguishable  from  other  parts  by  the 
absence  of  fibres.  The  microscope  shows  them,  however,  to  be 
still  farther  divisible  into  smaller  portions,  between  which  are 
seen  plates  of  cellular  substance,  and  if  we  attempt  to  pursue 
these  subdivisions  with  successively  greater  magnifying  powers, 
we  do  not  find  that  -^e  can  reach  their  limit.  The  above  descrip- 
tion is  particularly  applicable  to  the  saUvary,  lacrymal,and  pan- 
creatic glands. 

500.  The  second  modification  of  glandular  structure  occurs  in 
the  liver  and  the  kidneys,  in  which  it  is  impossible  to  trace  these 
successive  divisions  into  lobules,  after  we  have  distinguished  the 
primary  lobes  which  they  present.  Their  structure  exhibits  an 
uniform  and  even  tissue,  made  up  of  glandular  acini,  closely  united 
together  into  one  substance.  The  connecting  cellular  substance, 
if  any  such  exist,  is  short  and  very  small  in  quantity;  and 
hence  these  organs  may  be  torn  asunder  with  great  ease,  and 
their  ruptured  surfaces  present  the  appearance  of  granulations. 

501.  The  third  description  of  glands  applies  to  the  prostate,  to 
the  tonsils,  and  in  general  to  all  the  mucous  glands. 

502.  On  examining  the  course  of  the  blood-vessels,  the  small 
arteries  which  enter  into  a  gland  are  found  to  ramify  in  various 
ways  through  a  mass  of  cellular  texture.  But  it  is  a  matter  of 
great  uncertainty  what  specific  structure  intervenes  between  the 
secreting  arteries  and  the  commencement  of  the  excretory  ducts. 
Two  opinions  have  long  divided  anatomists  on  this  subject. 
Malpighi,  who  was  one  of  the  first  who  investigated  the  minute 
anatomy  of  glands,  asserted  that  the  acini  invariably  contain  a 
central  cavity,  or  follicle,  as  it  was  termed,  on  the  inner  surface 
of  which  the  arteries  are  distributed,  while  the  secreted  fluid  is 
collected  in  the  follicle,  and  conveyed  away  by  the  branch  of 
the  excretory  duct  which  arises  from  the  follicle.  He  considered 
the  mucous  glands  of  the  alimentary  canal,  which  undoubtedly 
present  a  structure  of  this  kind,  as  the  most  simple  forms  of 
glandular  structure ;  the  larger  glands  being  only  aggregations 
of  these  simpler  structures. 

503.  The  theory  of  Ruysch,  who  also  bestowed  extraordinary 
care  in  the  examination  of  glandular  structures,  is  founded  on 
the  supposed  continuity  of  the  extremities  of  the  arteries  with  the 
commencements  of  the  excretory  duct.  This  theory  is  so  far 
opposed  to  that  of  Malpighi,  that  itpre-supposes  all  the  glands  to 
consist  merely  of  an  assemblage  of  vessels  and  of  cellular  sub- 


GLANDULAR    APPARATUS.  221 

stance,  without  any  membranous  cavities  interposed  between  the 
arteries  and  excretory  ducts.  The  opportunities  of  dissection 
which  Ruysch  enjoyed,  and  his  unrivalled  skill  in  the  arts  of  in- 
jecting the  vessels,  and  tracing  their  modes  of  distribution,  gave 
great  weight  to  his  opinions,  which  seemed  to  be  immediate 
deductions  from  what  he  saw,  and  had  established  as  matters  of 
fact.  Fluids  could  be  made  by  injection  to  pass  very  readily 
from  the  blood-vessels  into  the  excretory  ducts,  both  in  the  kid- 
neys and  liver.  After  these  organs  have  been  accurately  injected, 
they  may  be  resolved,  by  subsequent  maceration,  into  small 
clusters  of  blood-vessels ;  what  Malpighi  had  represented  as 
hollow  acini,  seemed  to  be  in  reality  composed  of  a  congeries  of 
these  minute  vessels.  This  appeal  to  the  evidence  of  the  senses, 
and  the  admirable  preparations  which  supported  it,  brought  over 
almost  all  the  anatomists  of  that  time  to  the  opinion  of  Ruysch  ; 
and  Boerhaave  himself,  who  had  been  a  zealous  defender  of  the 
doctrine  of  Malpighi,  and  written  in  support  of  it,  was  at  length 
induced  to  adopt  the  views  of  Ruysch. 

504.  This  controversy  was  sustained  for  a  great  many  years 
in  the  schools  of  medicine  ;  and  the  opinions  of  anatomists  con- 
tinue even  at  the  present  time  to  be  divided  upon  this  subject. 
Probably  both  these  opinions  may  in  part  be  correct,  as  applied 
to  different  glands,  though  not  universally  trtie  ;  and  secretion 
may  perhaps  be  in  some  cases  performed  by  continuous  vessels, 
and  in  others  by  an  interposed  parenchyma,  of  a  cellular  or  more 
intricate  organic  apparatus. 

505.  As  the  structure  of  the  secreting  organs  admits  of  great 
variety,  it  may  be  useful  to  advert  to  some  of  the  terms  by  which 
these  minute  parts  have  been  designated.  The  terms  acini, 
cotulcB,  cryptce,  folliculi,  glandulcB,  lacuncB,  loculi,  utriculi,  have 
been  almost  promiscuously  used ;  being,  as  Bell  humorously  ob- 
serves, "  so  many  names  for  bundles,  bags,  bottles,  holes,  and 
partitions."  The  term  acinus  has  been  already  explained  (§499). 
CotuIcB  are  merely  superficial  hollow's,  from  the  surface  of  which 
the  secretion  is  poured  forth.  A  crypta  is  a  soft  body,  consisting 
of  vessels  not  completely  surrounded  with  a  membrane,  but  re- 
solvable by  boiling  or  maceration.  Follicles  are  little  bags  ap- 
pended to  the  extremity  of  the  ducts,  into  which  the  secretion  is 
made,  and  from  which  it  is  carried  ofi'  by  the  ducts.  LacuncB  are 
little  sacs,  opening  largely  into  certain  passages,  and  into  which 
generall}'  mucus  is  secreted. 

506.  The  excretory  ducts,  whatever  maybe  their  exact  origin, 
consist  at  first  of  an  infinite  number  of  capillary  tubes,  which, 
like  the  veins,  soon  unite  together  into  more  considerable  tubes. 
These  generally  pursue  a  straight  course  through  the  glandular 
tissue,  unite  wilh  one  another,  and  form  at  last  one  or  more  large 
tubes.     The  only  exception  to  this  general  proposition  occurs  in 

19* 


222  NUTRITIVE    rUNCTIONS. 

the  excretory  ducts  of  the  testicle,/which  pursue  a  singularly- 
tortuous  course  before  they  unite  into  the  vas  deferens  on  each 
side. 

507.  There  are  three  varieties  in  the  mode  of  termination, 
with  regard  to  the  excretory  ducts  of  glands.  In  the  first  case, 
the  ducts  unite  into  several  distinct  tubes,  which  open  separately, 
and  without  any  previous  communication.  Sometimes  these 
separate  apertures  are  met  with  in  a  more  or  less  distinct  pro- 
minence, as  in  the  breasts,  the  prostate,  and  the  sublingual  glands. 
At  other  times,  the  orifices  are  found  in  a  depression,  or  kind  of 
cul-de-sac,  as  in  tjie  tonsils,  and  in  the  foramen  coecum  of  the 
tongue.  In  the  second  case,  which  includes  the  greater  number 
of  glands,  their  fluids  are  poured  out  by  a  single  tube,  having  a 
simple  orifice.  In  the  third  case,  some  glands  deposit  the  pro- 
duce of  their  secretion  in  a  reservoir,  where  it  is  retained,  in 
order  to  be  expelled  at  particular  times  :  as  is  exemplified  in  the 
kidneys,  liver,  and  testicles.  In  this  case  there  must  be  two  ex- 
cretory tubes  ;  one  to  convey  the  secretion  from  the  gland  to  the 
reservoir,  and  the  other  to  transmit  it  to  its  final  destination. 
The  size  of  the  excretory  ducts  will,  of  course,  be  regulated  very 
much  by  their  number :  when  several  are  produced  from  one 
gland,  they  are  very  small,  and  sometimes  scarcely  perceptible. 
Those  which  are  single  are  longer  with  reference  to  the  size  of 
the  gland,  and  generally  pass  for  some  distance,  after  quitting 
the  gland.  In  the  pancreas,  however,  this  is  not  the  case,  the 
common  duct  being  concealed  in  the  substance  of  the  gland. 

508.  Whatever  the  arrangement  of  the  excretory  ducts  may 
be,  they  aU  pour  their  fluids,  either  on  the  surface  of  the  body, 
or  on  the  surface  of  some  of  the  mucous  membranes.  In  no 
instance  whatever  do  they  terminate  on  serous  or  synovial  sur- 
faces, or  in  the  common  cellular  membrane.  All  the  excretory 
ducts  are  themselves,  indeed,  provided  with  an  internal  mucous 
membrane,  which  is  a  continuation  of  the  cutaneous,  or  mucous 
surface  on  which  they  terminate.  In  addition  to  this  they  are 
furnished  with  an  exterior  coat,  formed  of  a  dense  and  compact 
membranous  and  fibrous  substance.  Every  excretory  duct  may 
therefore  be  considered  as  made  up  of  these  two  coats,  namely 
the  external  one,  which  is  membranous,  and  the  internal  one, 
which  is  mucous. 

509.  Amongst  the  latest  theories  relating  to  the  structure  of 
the  organs  of  secretion,  is  that  adopted  by  Muller,*  who  con- 
ceives that  the  glandular  organization  consists  essentially  of  a 
modification  of  the  excretory  duct,  the  remote  extremity  of 
which,  or  that   most  distant  from  the  discharging  orifice,  is 

*  De  Glandularum  Secernentium  Structura,  &c.     Lipsiae,  1830. 


PROPERTIES    OF    THE    SECRETIONS.  223 

closed  ;*  and  the  particles  of  which  exhibit  a  fine  net-work,  or 
plexus  of  minute  blood-vessels,  whence  the  secretion  is  in  the 
first  place  derived,  and  afterwards  conveyed  away  by  the  duct, 
into  the  cavity  of  which  it  is  poured.  The  duct  itself  may  be 
variously  divided  and  subdivided;  and  its  trunk  and  ramifica- 
tions may  be  variously  contorted  and  convoluted  in  different 
cases,  without,  however,  constituting  any  material  difference  in 
its  essential  structure. 

Sect.  III. — Arrangement  and  Properties  of  the  Secretions. 

510.  The  classification  of  the  various  secretions  which  are 
met  with  in  the  system  has  been  attempted  by  different  physiolo- 
gists, but  great  difficulty  has  presented  itself  in  fixing  on  a  princi- 
ple susceptible  of  being  practically  apphed  to  substances  of  such 
different  chemical  and  mechanical  properties,  as  are  those  which 
are  to  be  the  subjects  of  this  arrangement.  Haller,t  adopting 
for  his  basis  their  chemical  qualities,  distributed  them  under  the 
four  classes  of  aqueous,  mucous,  gelatinous,  and  oily.  Fourcroy 
arranged  them  under  eight  heads ;  namely,  the  hydrogenated, 
the  oxygenated,  the  carbonated,  the  azotated,  the  acid,  the  saline, 
the  phosphated,  and  the  mixed.J  Richerand  adopts  the  six 
classes  of  lacteous,  aqueous,  salivary,  mucous,  adipose,  and 
serous  ;§  and  Dr.  Young  those  of  aqueous,  urinary,  milky,  albumi- 
nous, mucous,  unctuous,  and  sebaceous. || 

511.  Dr.  Bostockl  distributes  the  secretions  under  the  eight 
heads  of  the  aqueous,  the  albuminous,  the  mucous,  the  gelatinous, 
the  fibrinous,  the  oleaginous,  the  resinous,  and  the  saline ;  an  ar- 
rangement which,  in  a  chemical  point  of  view,  is  the  clearest 
and  most  natural  that  has  yet  been  devised.**  We  shall  briefly 
notice  these  several  classes  in  the  order  above  stated. 

*  [This  arrangement,  sn  far  as  regards  the  biliary  system,  was  well  shown 
in  a  pathological  case,  which  fell  under  the  observation  of  Dr.  Dunglison.»  In 
consequence  of  cancerous  matter  obstructing  the  common  choledoch  duct,  the 
whole  excretory  apparatus  of  the  liver  was  enormously  distended  ;  ihe  common 
duct  was  dilated  to  the  size  of  the  middle  finger;  at  the  point  where  the 
two  branches  that  form  the  hepatic  duct  emerge  from  the  gland,  they  Avere 
large  enough  to  receive  the  tip  of  the  middle  finger,  and  as  they  were  propor- 
tionately dilated  to  their  radicles,  in  the  intimate  tissue  of  the  liver,  their  ter- 
mination in  a  blind  extremity  was  clearly  exhibited.  These  blind  extremities 
were  closely  clustered  together,  and  the  ducts  proceeding  from  them  were 
seen  to  converge,  and  to  terminate  in  the  main  trunk  for  the  corresponding 
lobe.] 

f  Elementa  Physiologiae,  v.  b.  2. 

X  Systeme  des  Connaiss.  Chym.  ix.  159.        §  Physiologie,  §  8B.  p.  235. 

II  Med.  Lit.  p.  109.  <j[  Physiology,  p.  480. 

**  [Other  classifications  have  been  founded  on  the  nature  of  the  secreting 
organ,  or  the  functions  of  the  secreted  fluid.  Bichat,  Magendie,  Lepelletier, 
and  others,  adopt  the  division  into  exhaled,  foUicuhr,  and  glandular  secre- 
tions (See  note  to  §  496).     Boyer,  Sabatier,  and  Adelon,  divide  them   into 

»Physiologj-,  ii.28!. 


224  NUTRITIVE    FUNCTIONS. 


1.   The  Aqueous  Secretions. 

512.  The  aqueous  secretions  are  those  which  consist  almost 
entirely  of  water,  and  of  which  the  properties  depend  principally 
on  its  watery  part;  any  other  ingredient  it  may  contain  being  in 
too  small  a  quantity  to  give  it  any  specific  characters.  The  two 
secretions  which  are  referable  to  this  class  are  the  cutaneous 
perspiration,  and  the  exhalation  from  the  lungs. 

513.  With  regard  to  the  fluid  of  perspiration,  it  seems  doubt- 
ful whether  it  contains  any  ingredients  that  are  constantly  pre- 
sent in  it,  or  that  are  essential  to  its  nature.  It  appears  to  differ, 
indeed,  considerably  in  difierent  individuals ;  and  varies  even  in 
the  same  individual,  according  to  the  state  of  the  system.  Its 
analysis  was  attempted  by  Berthollet,  and  afterwards  by  Four- 
croy ;  but  the  most  complete  examination  into  its  properties  is 
that  of  Thenard,  who  considers  it  to  be  essentially  acid,  and  that 
acid  to  be  the  acetic.  He  found  in  it,  also,  an  appreciable  quan- 
tity of  the  muriates  of  soda  and  potass,  with  traces  of  the  earthy 
phosphates  and  of  oxide  of  iron,  together  with  a  very  minute 
quantity  of  animal  matter.  Berzelius,  on  the  other  hand,  who 
has  examined  this  fluid  still  more  recently,  finds  the  free  acid  to 
be  the  lactic,  accompanied  with  the  lactate  of  soda.  An  elabo- 
rate analysis  of  the  fluid  of  perspiration  in  a  person  labouring 
under  disease,  has  also  been  made  by  Dr.  Bostock.*  The  aqueous 
exhalations  from  the  lungs  appears  to  be  so  perfectly  similar  to 
that  from  the  skin,  as  not  to  require  further  notice. 

2.   The  Albuminous  Secretions. 

514.  The  albuminous  class  of  secretions  are  numerous,  and 
comprehend  both  solid  and  fluid  substances.  We  have  already 
seen  that  all  membranous  and  fibrous  textures,  but  especially  the 
latter,  are  composed  principally  of  a  material  corresponding  in 
its  chemical  properties  to  coagulated  albumen  (see  §  165).  But 
there  are  many  fluid  secretions  which  contain  large  proportions 
of  this  ingredient  in  an  uncoagulated,  or  liquid  state  ;  such  as  the 
secretion  M'hich  exudes  from  serous  membranes,  and  also  occu- 
pies the  interstices  of  the  cellular  texture,  and  which  has  been 
termed  the  liquid  of  surfaces  (see  §  135).     This  fluid  also  con- 


recrementitial  secretions,  or  such  as  are  taken  up  by  internal  absorption,  and 
re-enter  the  circulation";  and  into  excremenlifial,  or  such  as  are  evacuated  from 
the  body,  and  constitute  the  excretions.  Some  have  added  a  third  division; 
the  recreinento-excrementitial,  in  which  a  part  of  the  humour  is  absorbed,  and 
the  remainder  ejected.] 

*  Medico-Chirurgical  Transactions,  xiv.  424. 


PKOPERTIES  OP  THE  SECRETIONS.  226 

tains,  besides  coagulable  albumen,  an  animal  matter  similar  to 
that  which  is  tbund  in  the  serosity  of  the  blood,  and  a  small 
quantity  of  the  usual  saline  matters  which  enter  into  the  compo- 
sition of  almost  all  animal  products. 

3.  Mucous  Secretions. 

515.  The  mucous  secretions  are  characterised  by  the  presence 
of  a  substance  which  does  not  pre-exist  in  the  blood,  but  which 
is  prepared  by  a  proper  secretory  or  glandular  action.  The 
properties  of  this  substance,  or  mucus,  have  been  already  noticed 
(§  301).  To  the  head  of  the  mucous  secretions.  Dr.  Bostock  is 
inclined  to  refer  also  the  saUva,  the  gastric  and  pancreatic  juices, 
the  tears,  and  the  semen. 

4.   The  Gelatinous  Secretions. 

516.  The  gelatinous  secretions  derive  their  essential  character 
from  the  predominance  of  gelatin  in  their  composition.  This 
substance  is  found  in  great  abundance  in  most  of  the  soUds,  and 
particularly  in  the  nnembranous  structures.  It  is  strictly  a  pro- 
duct of  secretion  ;  for  it  is  not  met  with  in  the  blood,  and  must 
therefore  be  formed  by  some  chemical  change  in  the  elements  of 
the  blood,  from  which  the  materials  for  its  preparation  are  derived. 
There  is  reason  to  believe,  from  the  discovery  of  Mr.  Hatchett  of 
the  possibility  of  converting  albumen  into  gelatin  by  digestion 
in  diluted  nitric  acid,  during  which  the  albumen  combines  with 
an  additional  quantity  of  oxygen,  that  some  change  analogous  to 
this  is  effected  in  the  Uving  body  during  the  process  of  its  secre- 
tion.    The  characteristic  properties  of  gelatin  have  already  been 

'  noticed  (§279). 

5.  The  Fibrinous  Secretions. 

517.  The  fibrinous  secretions  compose  the  fifth  class,  and  are 
so  named  from  their  correspondence  in  chemical  properties  to 
the  fibrin  of  the  blood,  which  fibrin  is  probably  the  source  from 
whence  these  secretions  derive  this  ingredient.  They  constitute 
the  organic  products  most  completely  animalized  in  their  che- 
mical constitution  ;  and  they  at  the  same  time  retain,  in  their 
physical  properties,  the  peculiar  cohesive  tendency  and  fibrous 
character  of  the  substance  from  which  they  are  produced.  The 
muscular  fibre  is  the  principal,  if  not  the  only  substance  which 
comes  under  this  head. 


226  NUTRITIVE    FUNCTION?. 


6.  The  Oleaginous  Secretions. 

518.  The  oleaginous  secretions  derive  their  essential  character 
from  the  presence  of  an  oily  ingredient.  They  compose  a  nu- 
merous and  varied  class,  comprehending  those  in  which  the  oil 
forms  the  greatest  part  of  the  substance,  and  those  in  which  it  is 
more  or  less  mixed  with  a  large  proportion  of  other  animal  prin- 
ciples. The  fat  is  the  principal  secretion  included  in  the  first 
division;  a  substance  which,  from  its  being  extensively  deposited 
ixi  various  parts  of  the  body,  must  evidently  be  formed  by  some 
peculiar  action  of  the  capillary  system  of  vessels.  As  it  consists 
almost  wholly  of  hydrogen. and  carbon,  we  must  conclude  that 
its  formation  is  effected  by  the  exclusion  of  nitrogen  and  oxygen 
from  the  proximate  elements  of  the  blood,  and  the  consequent 
intimate  combinations  of  their  carbon  and  hydrogen.  It  is  well 
known,  that  the  formation  of  fat,  by  whatever  chemical  operation 
it  may  be  effected,  often  proceeds  with  great  rapidity,  whenever 
circumstances  favour  its  production.  The  marrow,  as  was  for- 
merly observed,  belongs  also  to  this  class  of  secretions.  Dr. 
Bostock  is  disposed  to  refer  to  the  same  head  the  substance  termed 
cholesterine,  which  forms  the  basis  of  biliary  calculi. 

519.  Milk  is  a  secretion  owing  its  principal  characters  to  the 
oil  which  it  contains,  and  which  is  combined  with  albumen,  so 
as  to  form  a  kind  of  natural  emulsion.  When  collected  in  a 
separate  mass,  it  forms  the  well-known  substance  termed  butter. 
The  oily  particles  are,  however,  in  the  "original  state  of  milk, 
merely  diffused  by  mechanical  mixture  throughout  the  watery 
fluid,  as  is  evident  from  the  appearance  of  milk  under  the  micro- 
scope, when  it  exhibits  a  multitude  of  extremely  minute  globules 
swimming  in  a  transparent  liquor.  The  size  of  these  globules 
has  been  variously  estimated  by  different  observers,  and  indeed 
appears  to  be  by  no  means  uniform,  varying  in  different  instances 
from  the  10,000th  to  the  5000th  of  an  inch  in  diameter.  These 
oily  globules  have  a  tendency  to  adhere  together  when  the  milk 
is  allowed  to  rest,  and  in  the  course  of  a  few  hours  collect  at 
the  surface  in  the  form  of  cream,  and  by  further  coalescence 
they  compose  butter.  The  albumen  'may  be  obtained  from  the 
remaining  fluid  by  the  ordinary  means  of  coagulation,  and  con- 
stitutes curd,  which,  as  is  well  known,  is  the  basis  of  cheese.  The 
clarified  liquor  which  remains,  yields,  by  evaporation,  a  saccha- 
rine substance  capable  of  being  crystallized,  and  which  is  known 
under  the  name  of  sugar  of  milk.  It  differs  from  common  sugar 
by  being  less  soluble  in  water,  and  by  its  insolubility  in  alcohol. 
Milk  contains,  besides  these  ingredients,  several  saHne  substances, 
as  the  muriate  and  sulphate  of  potass,  the  phosphates  of  hmeand 
of  iron,  and  also  a  peculiar  animal  matter,  which  yields  a  pre- 
cipitate with  infusion  of  galls.     Milk  is  found  to  differ  from  the 


PROPERTIES  OF  -THE  SECRETIONS.  227 

blood,  and  from  most  of  the  animal  fluids,  by  the  base  of  its  salts 
being  potass  instead  of  soda.  A,  peculiar  acid,  called  the  lactic, 
is  formed  by  the  fermentation  of  milk,  and  even  alcohol  may  be 
obtained  during  this  process.  By  the  action  of  nitric  acid  on  the 
lactic  acid,  a  new  acid  is  produced,  termed  the  sacc/iolactic  or 
rnucic  acid,  which  unites  readily  with  alkaline  or  earthy  bases, 
and  forms  a  peculiar  class  of  salts. 

520.  The  substance  of  the  brain  bears  a  considerable  analogy 
to  the  oleaginous  secretions,  more  especially  to  that  of  milk ;  for 
it  consists  of  albumen  intimately  combined  with  a  peculiar  oily 
ingredient.  Rather  more  than  one-fourth  of  its  solid  substance, 
consists,  according  to  Vauquelin,*  of  a  fatty  substance,  and  nearly 
one-third  of  albumen;  the  remainder  being  composed  of  osmazome 
phosphorus,  acids,  salts,  and  sulphur. 

7.  The  Resinous  Secretions. 

521.  The  resinous  secretions,  which  compose  the  seventh  class, 
derive  their  specific  characters  from  an  ingredient  which  is  solu- 
ble in  alcohol,  and  is  analogous  to  resin.  Of  these  the  most 
remarkable  is  the  substance  which  constitutes  the  basis,  or  specific 
ingredient  of  bile.     (See  §  366.)  , 

522.  In  connexion  with  the  process  of  secretion  which  takes 
place  in  the  liver,  we  have  here  to  notice  the  remarkable  pecu- 
liarity which  occurs  in  the  mode  in  which  the  blood  is  circulated 
through  that  organ.  The  liver  is  supplied,  like  the  other  organs, 
with  arterial  blood,  by  the  hepatic  arteries,  which  are  branches 
from  the  aorta.  But  it  likewise  receives  a  still  larger  quantity 
of  venous  blood,  which  is  distributed  through  its  substance  by  a 
separate  set  of  vessels  derived  from  the  venous  system.  The  veins 
which  collect  the  blood  that  has  circulated  in  the  usual  manner 
through  the  abdominal  viscera,  unite  together  into  a  large  trunk, 
termed  the  vena  portce;  and  tiiis  vein,  on  entering  the  liver,  rami- 
fies like  an  artery,  and  ultimately  terminates  in  the  branches  of 
the  hepatic  veins,  which  transmit  the  blood  in  the  ordinary  course 
of  circulation  to  the  venae  cavse. 

523.  This  complex  arrangement  of  the  vessels  which  compose 
the  hepatic  system  has  lately  been  unravelled  with  singular  feli- 
city by  Mr.  Kiernan,  who,  in  a  paper  contained  in  the  Philoso- 
phical Transactions,  gives  an  account  of  his  valuable  discoveries, 
of  which  we  shall  present  the  following  abstract.  The  hepatic 
veins,  together  with  the  lobules  which  surround  them,  resemble 
in  their  arrangement  the  branches  and  leaves  of  a  tree,  the  sub- 
stance of  the  lobules  being  disposed  around  the  minute  branches 
of  the  veins  like  the  parenchyma  of  a  leaf  around  its  fibres.     The 

*  Annales  de  Chimie,  Ixxxi.  p.  37. 


228  NUTRITIVE    FUNCTIONS. 

hepatic  veins  may  be  divided  into  two  classes,  namely,  those  con- 
tained in  the  lobules,  and  those  contained  in  canals  formed  by 
the  lobules.  The  first  class  is  composed  of  interlobular  branches, 
one  of  which  occupies  the  centre  of  each  lobule,  and  receives 
the  blood  from  a  plexus  formed  in  the  lobule  by  the  portal  vein ; 
and  the  second  class  of  hepatic  veins  is  composed  of  all  those 
vessels  contained  in  canals  formed  by  the  lobules,  and  including 
numerous  small  branches,  as  well  as  the  large  trunks  terminating 
in  the  inferior  cava.  The  external  surface  of  every  lobule  is 
covered  by  an  expansion  of  Glisson's  capsule,  by  which  it  is  con- 
nected to,  as  well  as  separated  from,  the  contiguous  lobules,  and 
in  which  branches  of  the  hepatic  duct,  portal  veins,  and  hepatic 
artery,  ramify.  The  ultimate  branches  of  the  hepatic  artery 
terminate  in  the  branches  of  the  portal  vein,  where  the  blood 
they  respectively  contain  is  mixed  together,  and  from  which 
mixed  blood  the  bile  is  secreted  by  the  lobules,  and  conveyed 
away  by  the  hepatic  ducts  which  accompany  the  portal  veins  in 
their  principal  ramifications.  The  remaining  blood  is  returned 
to  the  heart  by  the  hepatic  veins,  the  beginnings  of  which  occupy 
the  centre  of  each  lobule,  and  when  collected  into  trunks,  pour 
their  contents  into  the  inferior  cava.  Hence  the  blood  whiclj^ 
has  circulated  through  the  liver,  and  has  thereby  lost  its  arterial 
character,  is,  in  common  with  that  which  is  returning  from  the 
■other  abdominal  viscera,  poured  into  the  vena  portas,  and  con- 
tributes its  share  in  furnishing  materials  for  the  biliary  secretion.*' 

524.  The  general  conclusion  which  Mr.  Kiernan  draws  from 
his  anatomical  researches  is,  that  the  hepatic  artery  is  destined 
solely  for  the  nutrition  of  the  liver,  and  has  no  direct  connections, 
except  with  the  branches  of  the  vena  portee,  after  its  own  blood 
has  become  venalized. 

525.  Urea  is  another  substance  of  a  resinous  nature,  which 
may  be  ranked  among  the  secretions,  and  which  constitues  the 
peculiar  or  specific  ingredient  in  urine.  It  is  remarkable  for 
containing  a  very  large  proportion  of  nitrogen,  which  is  by  this 
channel  discharged  from  the  system.     This  substance  has  been 

*  [This  is  one  view.  Analogy,  however,  would  suggest,  that  the  bile,  like^ 
every  other  secretion,  is  secreted  from  arterial  blood  ;  and  sufficient  function, 
it  appears  to  us,  remains  for  the  vena  porta,  in  being  the  agent  for  the  admix- 
ture of  the  various  heterogeneous  fluids,  which  are  received  into  the  stomach, 
and  pass  by  imbibition  into  the  venous  blood.  Were  there  no  capillary 
system  through  which  the  veins  of  the  stomach  and  duodenum  had  to  pass 
in  their  way  towards  the  heart,  these  fluids  would  be  but  imperfectly  mixed 
with  the  blood,  and  would  reach  the  central  organ  of  the  circulation  in  such  a 
state  of  concentration,  as  to  interfere  materially,  perhaps  fatally,  with  its 
functions.  The  capillary  distribution  of  the  vena  porta  in  the  liver  must 
obviate  this;  and  the  same  circumstances  will  aid  us  in  accounting  for  induration 
of  the  liver  in  the  spirit-drinker.  Light  is  thrown  on  the  subject  of 'he  secre- 
tion of  the  bile,  by  the  pathological  case  referred  to  in  the  note  to  §  509.] 


THEORY    OF    SECRETION.  229 

found  in  the  blood  of  animals  from  whom  the  kidneys  had  been 
removed. 

526.  The  peculiar  proximate  animal  principle,  termed  by 
Th6nard  osmazome,  is  referred  by  Dr.  Bostock  to  the  class  of 
resinous  secretions.  It  was  procured  originally  from  the  muscu- 
lar fibre,  of  which  it  forms  one  of  the  component  parts ;  and  it 
appears  to  be  the  ingredient  in  which  the  peculiar  flavour  and 
odour  of  the  flesh  of  animals  principally  depends.  It  is  found, 
however,  in  most  of  the  component  parts  of  the  body,  as  well 
solids  as  fluids.  The  cerumen,  or  ear-wax,  appears  also  from  the 
analysis  of  Vauquelin,  to  have  a  relation  to  the  resinous  secretions. 

8.    The  Saline  Secretions. 

527.  This  class  comprehends  all  those  fluids  in  which  saline 
ingredients  predominate  ;  they  are  very  numerous,  are  dispersed 
over  every  part  of  the  system,  and  are  more  or  less  mixed  with 
its  constituents.  They  consist  of  acids,  alkalies,  and  neutral  and 
earthy  salts.  The  following  are  the  acids  entering  into  the  com- 
position of  animal  substances,  and  which  are,  for  the  most  part, 
united  with  alkahne  or  earthy  bases ;  namely,  the  phosphoric, 
muriatic,  sulphuric,  fluoric,  hthic,  lactic,  benzoic,  carbonic,  and 
oxalic  acids  ;  and  perhaps  also  the  rosacic  and  the  amniotic.  Soda, 
potass,  and  ammonia,  are  found  in  almost  all  animal  fluids ;  but 
only  the  first  of  these  is  met  with  in  an  uncombined  state.  Of 
the  earths,  lime  is  by  far  the  most  abundant ;  magnesia  is  found 
in  small  quantity,  and  also  silex. 

528.  With  reference  to  their  saline  qualities.  Dr.  Bostock  pro- 
poses a  division  of  the  secretions  into  four  classes.  1.  Those 
which  are  nearly  without  any  admixture  of  salts.  2.  Those 
which  possess  a  definite  quantity  of  salts,  and  these  salts  different 
from  those  which  exist  in  the  blood.  3.  Those  containing  salts 
similar  both  in  their  nature  and  quantity  to  those  of  the  blood. 
And,  4.  Such  as  contain  salts  different  from  those  in  the  blood, 
and  which  are  also  variable  in  quantity.  The  fat,  the  sahva,  the 
liquor  of  surfaces,  and  the  urine,  may  be  given  as  examples  of 
each  of  these  divisions. 


Sect.  IV. —  Theory  of  Secretion. 

529.  The  nature  of  the  powers  and  processes  by  which  the 
products  of  secretion  are  prepared,  is  a  subject  involved  in  the 
greatest  obscurity.  There  is  scarcely  any  question  in  physiology, 
indeed,  the  investigation  of  which  presents  greater  difficulties. 
At  the  very  outset  of  the  inquiry  we  are  embarrassed  by  the  very 
imperfect  state  in  which  the  science  of  organized  chemistry  still 

20 


230  NUTRITIVE    FUNCTIONS. 

remains ;  a^nd  it  follows  as  a  necessary  consequence,  that  the 
precise  nature  of  tiie  chemical  changes  effected  during  secretion 
cannot  be  properly  understood.  That  the  operations  themselves 
are  of  a  chemical  nature,  must  be  inferred  from  their  results, 
consisting  of  substances  which  differ  in  most  instances  very  con- 
siderably from  the  constituents  of  the  blood,  whence  their  elements 
are  obtained.  The  blood  is  evidently  the  great  reservoir  of 
nutriment,  and  the  fountain  whence  all  the  materials  of  the 
secretions  are  derived.  In  a  few  instances,  as  we  have  seen,  the 
process  of  secretion  appears  to  consist  simply  of  the  separation 
of  some  of  the  proximate  principles  of  the  blood.  The  operation 
is,  in  that  ease,  more  of  a  mechanical  than  of  a  chemical  nature, 
and  is  analogous  to  mere  transudation  or  filtration,  subject,  how- 
ever, to  a  certain  power  of  selection  exercised  by  the  secreting 
organ.  In  the  greater  number  of  instances,  however,  the  product 
of  secretion  appears  to  be  a  new  formation,  differing  entirely 
from  any  of  the  proximate  principles  contained  in  the  blood,  and 
resulting  therefore  from  a  new  combination  of  its  elements. 

530.  Scarcely  any  light  has  been  thrown  on  this  mysterious 
subject  by  the'anatomical  investigation  of  the  organs  of  secretion. 
Their  intimate  structure  is  generally  so  minute  and  complicated, 
as  to  elude  the  severest  scrutiny  of  the  anatomist,  even  when  as- 
sisted by  the  best  optical  instruments.  What  increases  the  diffi- 
culty of  finding  any  clue  to  the  labyrinth,  is,  that  we  often  see 
parts  having  apparently  very  different  structures  giving  rise  to 
secretions  w^hich  are  nearly  identical  in  their  qualities  ;  and 
conversely,  we  see  substances  having  very  different  properties 
produced  by  organs  very  closely  resembling  each  other  in  their 
structure. 

531.  Sometimes  we  find  no  distinct  secretory  apparatus,  the 
whole  process  appearing  to  be  conducted  in  the  capillary  vessels, 
out  of  the  sides  of  which  the  product  seems  to  transude.  In 
other  instances,  the  secreted  fluid  exudes  from  the  smooth  surface 
of  a  membrane,  as  is  the  case  with  the  serous  secretions  in  all 
the  closed  cavitiefe  of  the  body,  such  as  those  of  the  peritoneum, 
pleura,  pericardium,  and  pia  mater.  The  matter  of  perspiration 
finds  its  way  through  the  skin  and  cuticle  without  any  visible 
ducts  or  even  pores,  appearing  simply  to  transude  through  the 
bibulous  substance  of  the  latter. 

532.  In  other  cases  we  find  the  secreting  membrane  furnished 
with  minute  processes,  or  villi,  from  the  extended  surface  of 
which  the  secretion  is  produced.     At   other  times,  there  are 

follicles,  or  crypts,  as  they  are  called,  into  which  the  secreted  fluid 
is  poured,  and  where  it  is  collected  previously  to  its  discharge 
by  its  appropriate  channels.  These  minute  cavities  are  occa- 
sionally grouped  together,  and  covered  with  a  denser  investing 
membrane  common  to  the  whole  assemblage,   constituting  the 


THEORY    OF    SECRETION.  231 

masses  which  are  called  glands.  But  no  practical  advantage 
has  arisen  from  the  technical  or  anatomical  classification  of 
glands,  neither  has  any  information  of  value  been  gathered  from 
the  examination  of  the  mode  in  which  the  blood-vessels  are  dis- 
tributed in  those  organs ;  although  this  mode  of  distribution  is 
apparently  very  diflerent  in  different  cases,  each  seeming  to  be 
intended  for  the  application  of  some  definite  but  unknown  princi- 
ple of  action.  Being  wholly  in  the  dark  with  regard  to  the 
specific  objects  intended  to  be  answered,  we  can  form  no  ra- 
tional conjecture  as  to  the  designs  of  nature  in  the  contrivances 
she  has  adopted.  We  see,  in  some  instances,  the  smaller  arteries 
divide  suddenly,  as  soon  as  they  have  reached  the  gland,  into 
very  numerous  minuter  branches,  like  ihe  fibres  of  a  hair  pencil. 
This  has  been  called  the  fencillated  structure.  The  arrangement 
in  other  cases  is  somewhat  different,  though  similar  in  its  princi- 
ple ;  the  minuter  branches  spi'eading  out  from  their  origin,  like 
rays  from  a  centre,  and  forming  a  stellated  structure.  Sometimes 
we  observe  the  arteries  of  the  secreting  organ  much  twisted  and 
contracted  in  their  course,  and  collected  into  spiral  coils,  before 
they  terminate.  All  the  varieties  of  secreting  organs,  as  Mr, 
Mayo  observes,  appear  to  be  only  contrivances  for  conveniently 
packing  a  large  extent  of  vascular  surface  into  a  small  compass. 
So  intricate,  indeed,  are  those  complex  arrangements,  that  it  is 
impossible  to  attempt  to  unravel  them  with  any  prospect  of  suc- 
cess. In  a  word,  nothing  hitherto  known  relative  to  the  structure 
of  glands  has  explained  the  mode  in  which  they  act,  or  has 
thrown  any  light  upon  the  nature  of  the  substances  they  produce. 
533.  In  this,  as  in  other  subjects,  where  facts  are  wanting  for 
its- elucidation,  we  find  numberless  hypotheses 'proposed  in  their 
stead.  Secretion  was  formerly  pronounced  to  be  a  species  of 
fermentation,  by  those  who  could  attach  no  definite  idea  to  the 
term  they  emploj^ed.  Others  sought  to  explain  secretion  by  vari- 
ous mechanical  hypotheses,  supposing  it  to  be  the  result  of  a 
mere  organic  filtration  of  particles  already  existing  in  the  blood  ; 
they  racked  their  imaginations  for  the  invention  of  forms  of 
apertures  and  channels  capable  of  admitting  particles  having 
corresponding  figures,  and  of  refusing  a  passage  to  the  rest. 
Leibnitz  compared  the  glands  to  filters,  of  which  the  pores  were 
originally  impregnated  with  a  particular  fluid,  which  fluid  would 
therefore  be  allowed  to  pass,  to  the  exclusion  of  all  other  fluids, 
in  the  same  manner  as  a  paper  impregnated  with  oil  prevents  the 
passage  of  water,  but  allows  oil  to  be  transmitted.  This  unche- 
mical  theory  proceeded  on  the  hypothesis  that  all  the  secreted 
matters  pre-exist  ready  formed  in  the  blood,  and  require  only  to 
be  separated  by  the  glands  ;  a  supposition  of  which  the  latter 
improvements  in  animal  chemistry  have  sufficiently  exposed  the 
falsehood. 


232  NUTRITIVE    FUNCTIONS. 

534.  But  even  admitting  the  operation  of  the  secretory  organs 
to  be  wholly  of  a  chemical  nature,  we  are  still  completely  in  the 
dark  as  to  the  means  which  nature  employ's  in  the  hidden  labora- 
tories of  organization;  nor  do  they  appear  in  any  way  reconcile- 
able  to  the  ordinary  laws  of  chemical  affinities  to  which  inorganic 
substances  are  obedient.  The  means  employed  are  superior  to 
mere  chemical  agency,  in  the  same  degree  as  the  operations  of 
chemical  affinities  transcend  those  of  mechanism.  All  that  we 
can  conceive  to  be  the  office  of  the  different  series  of  vessels, 
which,  by  ramifying  into  smaller  and  smaller  tubes,  have  the  ef- 
fect of  subdividing  the  blood,  as  by  a  strainer,  to  certain  degrees 
of  tenuity,  is  that  merely  of  preparing  it  for  the  changes  it  is  to 
undergo  in  that  stage  of  the  process  in  which  the  essential  con- 
version consists.  Farther  than  this  we  cannot  venture  to  specu- 
late, knowing,  as  we  do,  so  imperfectly  either  the  changes  produ- 
ced, or  the  means  by  which  these  changes  can  be  effected ;  unless, 
indeed,  we  endeavour  to  call  to  our  assistance  the  power  of  gal- 
vanism, which  has  been,  in  modern  times,  proved  to  be  so  impor- 
tant and  powerful  an  agent  in  effecting  changes  of  chemical  com- 
position. But  the  analogy  is  yet  too  vague  to  serve  as  the  basis 
of  any  solid  theory. 

535.  There  is  no  doubt  that  in  many  cases  the  process  of  secre- 
tion is  considerably  influenced  by  the  condition  of  the  nervous 
powers.  Thus  the  section  of  the  par  vagum  is  invariably  follow- 
ed by  the  diminution  or  total  suppression  of  the  gastric  juice,  and 
by  the  increase  of  the  secretion  of  bronchial  mucus.  Under  these 
circumstances,  the  secretions  of  the  stomach  are  restored  by  di- 
recting a  stream  of  galvanic  electricity  through  the  nerves  that 
have  been  divided;  a  fact  which  is  explicable  only  in  one  of  two 
ways,  namely,  either  by  supposing  that  the  galvanic  influence  is 
the  same  as  the  influence  derived  from  the  nerves,  or  that  galvan- 
ism excites  a  fresh  exertion  of  the  nervous  influence,  in  the  por- 
tion of  the  nerve  on  which  its  action  is  directed. 

536.  On  the  whole,  as  it  appears  impossible  to  refer  the  pheno- 
mena of  secretion  to  any  of  the  other  known  laws  of  matter,  whe- 
ther chemical  or  mechanical,  it  becomes  us  to  acknowledge  our 
ignorance  of  the  real  causes  that  produce  them,  and  to  ascribe 
them  to  the  agency  of  those  powers  to  which  we  have  given  the 
name  of  the  organic  affinities;  by  which  term,  however,  we  are 
far  from  wishing  to  imply  that  these  affinities  essentially  differ  in 
their  kind  from  the  ordinary  chemical  affinities  which  regulate  the 
coiTibinations  of  the  same  elements  in  unorganized  bodies ;  but 
only  that  their  operation  is  modified  by  the  peculiarity  of  the  cir- 
cumstances in  which  they  are  placed.  One  of  the  principal  causes 
of  this  peculiarity  appears  to  be  the  influence  of  the  nermus power ; 
a  power  carefully  to  be  distinguished  from  the  sensorial  powers 
hereafter  to  be  considered,  and  wholly  of  a  physical  character 


STRUCTURE    OF    THE    ABSORRENT    SYSTEM.  233 

exercised  by  the  nervous  system,  and  controlling  the  actions 
of  the  blood-vessel,  and  more  especially  of  the  capillaries,  and 
also  those  chemical  changes  which  produce  the  evolution  of  ani- 
mal heat,  regulating  in  a  particular  manner  the  processes  of  secre- 
tion, and  in  some  instances  producing  the  contractions  of  the  mus- 
cles in  a  v^'ay  directed  to  some  beneficial  purpose,  and  in  cases 
where  the  interference  of  the  mind  does  not  take  place.  But  of 
this  latter  exercise  of  the  nervous  power  we  shall  have  to  speak 
more  at  large  when  we  come  to  treat  of  the  involuntary  motions. 


CHAPTER    XL 


ABSORPTION. 


537.  The  objects  of  the  function  of  absorption  are,  first,  the 
removal  of  those  materials  which  have  become  unserviceable  and 
noxious  from  the  situations  where  their  presence  is  injurious  ;  and, 
secondly,  their  transmission  into  the  general  mass  of  circulating 
fluids.  The  lymphatic  vessels  are  appropriated  to  this  office,  and 
form,  with  the  lacteals,  which  perform  a  similar  service  with 
respect  to  the  chyle,  one  extensive  system  of  vessels  denorni- 
nated  the  ahsorhents. 


Sect.  I. — Structure  of  the  Absorbent  System. 

538.  The  absorbent  system,  then,  is  understood  to  compre- 
hend two  sets  of  vessels,  distinguished  only  by  a  certain  dif- 
ference in  the  office  which  they  perform,  but  agreeing  in  their 
structure  and  general  functions.  The  first  are  the  lacteals, 
which,  as  we  have  seen,  are  appropriated  to  the  conveyance  of 
the  chyle,  or  nutritious  fluid  prepared  in  the  intestines,  into  the 
general  reservoir  of  nutriment,  the  sanguiferous  system.  The 
second  are  the  lymphatics,  which  perform  a  similar  office  with 
regard  to  the  materials  of  the  body  itself,  that  have  become 
either  useless  or  noxious,  or  with  respect  to  foreign  substances 
applied  to  the  external  surface,  or  introduced  into  any  part  of  the 
body.  The  same  general  description,  as  to  structure,  will  apply 
to  both  these  systems  of  vessels. 

539.  Absorbent  vessels  are  met  with  in  almost  every  part  of 
the  body.  They  may  be  regarded  as  analogous,  or  even  supple- 
mentary in  their  office,  to  the  veins;  and,  accordingly,  their 
structure  and   mode  of  distribution  are  very  similar  to  that  por- 

20* 


334 


NUTRITIVE    PITNCTIONS. 


tion  of  the  sanguiferous  system.  The  absorbents  arise  from  the 
various  surfaces  of  the  body,  external  as  well  as  internal,  by  very 
minute  branches  ;  but  whether  these  branches  commence  by  open 
orifices,  or  imbibe  the  fluids  they  receive  through  the  medium 
of  their  coats,  we  have  hitherto  no  certain  knowledge.  The 
lesser  branches  of  the  lymphatics,  like  those  of  the  veins,  join 
together  to  form  larger  branches ;  while  these  again  successively 
unite  into  larger  and  larger  trunks,  till  they  conduct  their  con- 
tents into  the  veins,  into  which  they  open.  They  communicate 
with  one  another  freely  in  their  course;  and  these  connexions 
are  frequently  so  numerous  and  intricate,  as  to  form  an  extensive 
net-work,  or  plexus  of  lymphatic  vessels.  They  are  furnished 
with  numerous  valves,  which,  like  those  of  the  veins,  are  of  a 
semilunar  or  parabolic  form,  disposed  in  pairs,  and  placed  so 
as  to  prevent  any  retrograde  motion  of  the  contents  of  the  ves- 
sels. 

540.  Like  the  veins,  the  absorbents  have  thin  and  transparent 
coats,  which  are  possessed  of  considerable  strength,  so  as  to 
admit  of  being  distended  much  beyond  their  natural  size,  without 
being  ruptured,  by  injected  fluids  urged  into  them  with  considera- 
ble force.  When  they  are  thus  enlarged  by  injection,  they 
resemble  a  string  of  beads ;  an  appearance  arising  from  the 
numerous  valves  they  contain,  and  which  occur  at  short,  but 
generally  unequal  intervals. 

541.  The  absorbent  vessels  are  formed  of  two  coats,  which  in 
the  principal  trunks  are  very  distinct  from  each  other.  The  ex- 
ternal coat  is  the  one  which  constitutes  the  chief  bulk  of  the  ves- 
sel, and  gives  it  its  general  form.  It  is  of  a  membranous  struc- 
ture, and  is  connected  with  the  surrounding  parts  by  a  loose  tissue 
of  cellular  substance.  It  exhibits,  where  it  joins  the  inner  coat, 
more  or  less  of  a  fibrous  structure ;  and  some  anatomists  have 
pretended  even  to  have  perceived  traces  of  muscular  fibres  at 
this  part.  The  interior  membrane  which  lines  the  former,  is  more 
thin  and  deUcate;  and  it  is  by  duplicatures  of  this  membrane  that 
the  valves  are  formed.  These  valves  are  remarkable  for  their 
strength,  not  being  rupiured  without  the  greatest  diificulty. 

542.  The  continuity  of  the  course  of  the  absorbents  is  interrup- 
ted in  a  variety  of  places,  by  small  rounded  bodies,  which  have 
been  called  lymphatic  or  conglobate  glands,  and  which  are  situate 
on  the  track  both  of  the  lacteals  and  lymphatics.  They  seem  to 
have  a  similar  relation  to  the  absorbents  which  the  ganglia  have 
to  the  nerves ;  and  they  have,  on  that  account,  been  sometimes 
called  the  lymphatic  ganglia.  They  are  of  various  sizes ;  the 
smaller  being  placed  near  the  origin,  and  the  larger  on  the  more 
considerable  trunks  of  these  vessels.  Those  of  greatest  magnitude 
are  situate  at  the  root  of  the  mesentery,  in  the  course  of  the  lac- 
teals, and  are  denominated  the  mesenteric  glands.     These  glands 


STRUCTURE    OF    THE    ABSORBENT    SYSTEM.  235 

are  sometimes  detached,  and  sometimes  in  groups  or  clusters,  and 
commonly  of  an  oblong  rounded  shape,  and  somewhat  flattened, 
bearing  some  general  resemblance  to  an  almond.  Their  colour 
is  a  whitish  red,  of  more  or  less  intensity,  according  as  they  are 
situate  more  externally.  Those  of  the  mesentery  are  nearly  white  ; 
those  of  the  spleen  brown:  and  those  belonging  to  the  lungs  are 
of  a  very  dark,  or  almost  black  hue.  Each  gland  is  enveloped 
in  a  thin,  fibrous,  and  very  vascular  membrane,  surrounded  with 
dense  cellular  tissue,  which  sends  down  processes  into  the  sub- 
stance of  the  gland,  dividing  it  into  numerous  compartments. 

543.  It  would  appear  from  the  extensive  researches  of  Mascag- 
ni,  that  every  absorbent  vessel,  during  its  course,  passes  through 
one  or  more  of  these  glands.  Previous  to  their  penetrating  into 
the  gland,  each  absorbent  trunk  branches  out  suddenly  into  nume- 
rous subdivisions,  distinguished  by  the  name  of  vasa  inferentia. 
These  vessels  are  distributed  on  the  surface  of  the  gland  in  a  ra- 
diating form,  so  as  to  surround  it  with  a  kmd  of  net-work.  After 
they  have  entered  the  gland,  their  course  becomes  extremely  dif- 
ficult to  unravel,  from  their  numerous  and  minute  ramifications, 
their  tortuous  course,  and  their  frequent  communications.  It  would 
appear,  however,  that  while  some  acquire  and  retain  an  extreme 
degree  of  tenuity,  others  become  dilated,  and  form  cells,  somewhat 
resembling  the  erectile  tissue  formerly  described.  That  portion 
of  the  vessels  which  is  destined  again  to  collect  the  fluid,  and  con- 
duct it  forwards  on  its  course,  appears  to  have  a  similar  structure, 
presenting  a  congeries  of  minute  ramifications,  and  of  dilatations 
or  cells. 

544.  By  the  successive  reunion  of  these  branches,  they  are  all 
collected  into  a  certain  number  of  trunks  which  emerge  from  the 
gland,  under  the  name  of  the  liasa  efferentia.  The  total  capacity 
of  the  vasa  efferentia  is,  in  general,  less  than  that  of  the  vasa  in- 
ferentia. Large  clusters  of  lymphatic  glands  exist  in  the  neck, 
the  groin,  the  axilla,  as  well  as  in  the  course  of  the  greater  trunks, 
not  far  from  their  termination  in  the  thoracic  duct. 

545.  The  great  trunks  of  the  lymphatics  occupy  two  principal 
.  situations ;  the  one  near  the  surface,  and  the  other  more  deeply 

seated ;  and  for  the  most  part  they  follow  the  course  of  the 
veins.  The  main  branches  are  finally  reduced  to  three  or  four 
great  trunks,  which  terminate  for  the  most  part  in  the  thoracic 
duct.  This  is  a  vessel  of  considerable  size,  passing  upwards  close 
to  the  spine,  in  a.somewhat  tortuous  course,  to  about  half  an  inch 
above  the  trunk  of  the  left  subclavian  vein.  It  then  bends  down- 
wards, and  opens  into  that  vein,  nearly  at  its  junction  with  the 
jugular  vein.  Another  similar,  but  shorter  trunk,  is  found  on  the 
opposite  side,  which  pours  its  contents  into  the  right  subclavian 
vein. 

546.  The  nature  of  the  lymph,  or  fluid  contained  in  the  lym- 


236  NUTRITIVE    FUNCTIONS, 

phatic  vessels,  is  but  imperfectly  known,  in  consequence  of  the 
difficulty  of  collecting  it  in  sufficient  quantity  for  examination. 
When  viewed  under  the  microscope  it  is  seen  to  contain  a  num- 
ber of  colourless  globules,  much  smaller  and  less  numerous  than 
the  red  particles  of  the  blood.*  Mr.  Brande  separated  a  small 
quantity  of  albumen  from  it  by  the  application  of  voltaic  elec- 
tricity: he  found  that  it  also  contained  some  muriate  pf  soda. 
Berzelius  states  that  the  lactates  are  likewise  present  in  it, 
derived,  as  he  supposes,  from  the  decomposed  substance  of  dif- 
ferent parts  of  the  body,  which  is  taken  up  by  the  absorbents. 
Reuss,  Emmert,  and  Lassaigne  obtained  fibrin  from  the  lymph 
of  the  horse,  and  Nasse  and  Miillerf  obtained  some  also  from 
human  lymph.  When  removed  from  the  body,  this  fluid  fibrin 
coagulates  in  less  than  ten  minutes.  Besides  the  above  ingre- 
dients, Tiedemann  and  Gmelin  state  that  the  lymph  contains 
salivary  matter,  osmazome,  carbonates,  sulphates,  muriates,  and 
acetates  of  soda  and  potass,  with  phosphate  of  potass. 


Sect.  II. — Function  of  the  Absorbents. 

547.  Whilst  the  office  of  the  lacteals  is  confined  to  the  absorp- 
tion of  a  particular  kind  of  fluid,  namely,  the  chyle,  the  power 
of  the  lymphatics  extends  to  the  removal  of  every  species  of 
matter  which  enters  into  the  composition  of  the  body,  as  occa- 
sion may  require,  as  also  various  extraneous  substances  that  may 
happen  to  be  placed  in  contact  with  their  mouths.  Whether  the 
lymphatics  have  the  power  of  taking  up  solid  materials  of  the 
body  without  their  being  previously  liquified,  is  a  point  which  is 
yet  far  from  being  determined.  We  are  certain  that  the  hardest 
and  densest  structures,  such  as  the  bones,  are  liable  to  absorption, 
in  various  instances,  not  only  during  the  natural  processes  of  their 
formation  ?nd  growth,  but  also  on  occasions  when  they  are 
subjected  to  extraneous  pressure.  We  find  that  the  bones  are 
modelled  by  the  pressure  even  of  soft  living  parts,  during  their 
natural  growth,  or  morbid  enlargement.  The  rapid  disap- 
pearance of  the  red  tinge,  which  the  use  of  madder  in  the  food 
had  communicated  to  the  bones,  when  that  food  is  discontinued, 
has  been  supposed  to  warrant  the  conclusion  that  the  particles  of 
bones  are  at  all  times  undergoing  a  quick  periodical  renova- 
tion. But  it  appears  from  more  recent  inquiries,  that  this  in- 
ference has  been  too  hastily  drawn :  the  change  of  colour  being  the 
result  of  the  disappearance  of  the  colouring  particles  of  the  mad- 
der only,  without  its  being  at  all  necessary  to  suppose  that  the 

*  Miiller's  Elements  of  Physiology,  by  Baly,  p.  258.        f  Ibid.  p.  259. 


VENOUS    ABSORPTION.  237 

earthy  particles  of  the  bone  are  themselves  changed,  or  succes- 
sively absorbed  and  deposited  along  with  the  madder.* 

548.  The  nature  of  the  process  by  which  the  particles  to  be 
absorbed  are  prepared  for  being  taken  up  by  the  lymphatics ;  the 
mode  in  which  they  are  conveyed  to  the  orifices  of  these  ves- 
sels, if  indeed  they  take  their  rise  like  the  lacteals,  by  open 
orifices ;  and  the  power  by  which  they  find  their  way  into  these 
vessels,  and  are  conveyed  onwards  to  their  termination  in  the 
thoracic  duct ;  are  all  subjects  involved  in  the  greatest  obscurity. 
Capillary  attraction  is  the  only  power  to  which  the  rise  of  the 
lymph  in  the  lymphatic  vessels  appears  to  bear  any  near  resem- 
blance ;  but  the  analogy  is  far  too  vague  and  remote  to  be  of 
much  assistance  to  us  in  the  solution  of  the  difficulty.  How  far 
the  powers  recently  discovered,  and  which  have  been  termed 
endosmose  and  exosmose,  whereby  membranous  substances  allow 
the  transmission  in  a  certain  direction,  of  particular  fluids  only, 
to  the  exclusion  of  others,  are  concerned  in  the  phenomena,  re- 
mains a  subject  for  future  investigation.  It  seems  likely,  how- 
ever, to  throw  some  light  on  the  processes  both  of  secretion  and 
absorption ;  and  perhaps  may  furnish  an  explanation  of  the 
selection  evinced  by  the  lymphatics  in  absorbing  certain  mate- 
rials in  preference  to  others.  Absorption  takes  place  with  great 
facility  from  the  mucous  surfaces,  and  also  from  those  formed 
by  ulceration.  It  also  takes  place  from  the  surface  of  serous 
membranes,  though  with  less  activity.  From  the  external  surface 
of  the  skin,  absorption  takes  place  with  great  difficulty,  and  only 
under  particular  circumstances,  as  when  substances  ai-e  forcibly 
pressed  through  the  cuticle.  Considerable  absorption  often  oc- 
curs from  the  interior  of  the  pulmonary  air-cells.  ■''  Absorption 
from  the  surface  of  the  body  is  diminished,  or  even  suspended, 
by  greatly  diminishing  the  pressure  of  the  atmosphere  on  the 
part,  as  by  the  apphcation  of  a  cupping-glass. 


Sect.  III. —  Venous  Absorption. 

I 
549.  Soon  after  the  discovery  of  the  lymphatic  absorbents,  a 
keen  controversy  arose  as  to  whether  absorption  was  performed 
exclusively  by  these  vessels :  for  it  was  contended  by  many  that 
the  veins  assisted  in  this  process,  and  occasionally  acted  as  ab- 
sorbinaj  vessels.  The  arguments  and  reasonings  of  Hunter  and 
Monro,  founded  on  numerous  experiments,  appeared  to  nave 
completely  decided  the  question,  and  established  the  exclusive 
agency  of  the  lymphatics  in  the  performance  of  this  function. 

*  See  a  paper  on  this  subject  by  Mr.  Gibson,  in  the  Memoirs  of  the  Literary 
and  Philosophical  Society  ot'  Manchester.     Second  Series,  i.  146. 


238 


NUTRITIVE    FUNCTIONS. 


Of  late  years,  however,  the  ancient  opinion  has  been  revived  by 
Magendie  and  others,  who  seem  to  have  satisfactorily  proved 
that  absorption  is  occasionally  carried  on  by  the  veins  themselves; 
and  that  many  of  the  lesser  lymphatic  vessels  terminate  in  the 
small  veins,  instead  of  proceeding  to  the  thoracic  duct.  It  has 
been  ascertained,  for  instance,  that  where  the  great  lymphatic 
trunks  are  tied  in  animals,  substances  injected  into  the  stomach 
quickly  find  their  way  into  the  general  mass  of  circulating  blood, 
and  may  be  detected  in  the  urine.  Poison,  introduced  into  a 
portion  of  intestine,  completely  isolated  from  the  rest  of  the  body, 
with  the  exception  only  of  the  artery  and  the  vein,  produces  its 
effect  upon  the  system  nearly  in  the  same  time  as  if  the  natural 
connexions  had  been  preserved.  The  same  result  takes  place 
when  a  limb  is  separated  from  the  body,  by  dividing  every  part 
excepting  the  artery  and  the  vein,  and  the  poison  is  introduced 
under  the  skin.  It  proves  fatal  in  the  usual  time,  ahhough  the 
only  medium  through  which  its  influence  can  be  supposed  to  be 
transmitted  is  the  circulating  blood,  which  must  therefore,  it  is 
concluded,  have  received  the  poison  by  venous  absorption. 

550.  The  subject  of  venous  absorption,  and  of  the  connexion 
between  the  lymphatic  and  sanguiferous  systems,  has  of  late 
years  much  occupied  the  attention  of  physiologists.  Great  labour 
has  been  bestowed  on  its  investigation  by  Fohmann,  Lauth,  and 
Panizza,  on  the  continent ;  and  recently  in  this  country  by  Dr. 
Hodgkin,  who  was  appointed,  with  others,  to  form  a  committee 
for  conducting  this  inquiry  by  the  British  Association  for  the 
advancement  of  science.  A  short  provisional  report  by  this 
gentleman  is  pubhshed  in  the  report  of  the  sixth  meeting  of  that 
association,  in  vol.  v.  p.  289,  to  which  we  must  refer  our  readers, 
as  containing  the  latest  information  on  this  important  branch  of 
physiology.  Many  facts  render  it  exceedingly  probable  that  the 
contents,  both  of  the  lacteals  and  of  the  lymphatics,  are  inter- 
mixed with  that  of  the  veins  in  the  lymphatic  glands.* 

Sect.  IV. — Effects  of  Absorption. 

551.  The  absorbents  have  a  powerful  influence  in  modifying 
the  fluid  secretions,  as  well  as  the  solid  materials  of  the  body. 
Their   agency  in   assisting  the   arteries  and  capillaries  which 

*  [A  careful  investigation  of  the  whole  of  this  interesting  subject  leads  us 
to  infer,  that  the  chj'liferous  and  lymphatic  vessels  form  only  chyle  and  lymph, 
refusing  all  other  substances  with  the  exception  of  saline  matters,  which  enter 
probably  by  imbibition  ;  that  the  veins  admit  every  liquid  which  possesses  the 
necessary  degree  of  tenuity  ;  and  that  whilst  all  the  absorptions,  which  require 
the  substances  acted  upon  to  be  decomposed  and  transformed,  are  effected  by 
the  chyliferous  and  lymphatic  vessels,  those  that  are  sufficiently  thin,  and 
demand  no  alteration,  are  accomplished  directly  through  the  coats  of  the  veins 
by  imbibition.     See  Dunglison's  Physiology,  3d  edit.  ii.  81.] 


FUNCTION    OF    THE    LYMPHATIC    GLANDS.  239 

effect  the  growth  and  nutrition  of  the  body  is  beautifully  exem- 
plified in  the  processes  of  ossification  and  of  dentition,  where 
the  changes  can  more  easily  be  followed  than  in  the  progressive 
modifications  of  softer  organs.  All  these  facts  lead  to  the  con- 
clusion that  the  absorbent  vessels  possess  very  extensive  powers 
in  modelling  the  organization  of  the  body  in  all  its  parts.  In  the 
progress  of  life,  various  changes  are  efl^ected  in  the  size  and  form 
of  different  parts,  either  in  the  natural  course,  or  from  the  effects 
of  disease.  We  see  various  organs  diminish  in  size,  sometimes 
with  great  rapidity,  from  the  general  absorption  of  their  sub- 
stance, or,  as  it  has  been  termed,  from  interstitial  absorption ; 
and  in  other  instances  from  causes  external  to  the  organ  affected, 
such  as  pressure  or  ulceration ;  in  which  cases  the  process  is 
denominated  progressive  absorption.  In  some  structures,  espe- 
cially those  which  are  but  scantily  furnished  with  vessels,  the 
renewal  of  particles  is  much  slower  than  in  more  vascular  parts  ; 
but  even  these  are  in  a  certain  degree  subject  to  a  constant  ab- 
sorption and  renewal  of  their  particles. 


Sect.  V. — Function  of  the  Lymphatic  Glands. 

552.  Of  the  offices  performed  by  the  lymphatic  glands,  which 
are  so  numerously  interspersed  in  the  course  of  the  vessels,  we 
are  still  in  profound  ignorance ;  an  ignorance  which  is  little  to 
be  wondered  at,  when  it  is  considered  that  we  are  but  imperfectly 
acquainted  with  their  structure,  and  the  course  which  the  branches 
of  the  absorbents  take  in  the  interior  of  those  bodies,  and  that  we 
are  also  very  much  in  the  dark  with  regard  to  the  nature  of 
glandular  action,  and  of  the  changes  which  it  induces  on  the 
fluids  subjected  to  its  influence.  These  glands  may  either  be 
proper  secreting  organs,  intended  to  prepare  a  peculiar  substance, 
which  is  to  be  mixed  with  the  chyle  and  lymph,  in  order  to  assi- 
milate them  more  and  more  to  the  nature  of  the  blood  with  which 
they  are  to  be  united;  or  they  may,  by  their  tortuous  passages, 
offer  a  mechanical  obstruction  to  the  progress  of  these  fluids,  and 
thus  occasion  in  them  spontaneous  changes  in  the  arrangement 
of  their  constituent  parts.  This  latter  view  of  the  uses  of  the 
glands  was  taken  by  Mascagni,  and  he  endeavoured  to  confirm 
it  by  pointing  out  differences  in  the  nature  of  the  lymph  before 
and  after  it  had  passed  through  a  gland ;  but  this  fact,  if  esta- 
blished, would  be  equally  explicable  on  either  hypothesis.  The 
greater  size  and  vascularity  of  these  glands  in  youth,  when  the 
growth  of  the  organs  is  most  rapid,  would  lead  to  the  belief  that 
their  functions  are  of  importance  in  the  elaboration  of  nutritive 
matter  to  meet  the  greater  demand  for  the  materials  of  growth 
at  that  period  of  life. 


240  NUTRITIVE    FUNCTIONS. 


CHAPTER     XII. 


EXCRETION. 

553.  The  expulsion  from  the  system  of  those  materials  which 
are  useless  or  noxious,  is  the  office  of  excretion ;  and  the  organs 
or  channels  by  which  it  is  performed  are  called  the  excretory  or- 
gans. They  consist  of  the  lungs,  the  skin,  the  kidneys,  and  pro- 
bably also  the  liver. 


Sect.  I. — Excretory  Function  of  the  Lungs. 

554.  Of  the  office  of  the  lungs  in  purifying  the  blood  from  its 
redundant  carbonaceous  matter,  we  have  already  fully  treated. 
Besides  carbon,  or  rather  carbonic  acid,  a  large  quantity  of  water 
is  also  exhaled  by  means  of  the  lungs.  As,  however,  there  is 
reason  to  beheve  that  considerable  absorption  of  water  also  takes 
place  from  the  same  surface,  the  amount  of  loss  sustained  by  the 
united  operation  of  these  two  functions  is  only  the  excess  of  the 
exhalation  over  the  absorption.  < 


Sect.  II. — Excretory  Function  of  the  Skin.* 

555.  We  have  already  given  the  results  of  the  chemical  analysis 
of  the  matter  of  perspiration,  in  our  account  of  the  aqueous  secre- 
tions (§  514).  The  chief  ingredient  is  unquestionably  water ;  and 
the  average  amount  of  water  which  escapes  from  the  body  through 
the  channel  of  the  skin,  has  been  very  variously  estimated  by  dif- 
ferent physiologists;  for,  indeed,  it  is  hardly  possible  to  arrive  at 
any  definite  conclusion  on  this  subject,  from  the  great  variations 
that  occur  even  in  the  same  individual  at  difiierent  times,  especially 
according  to  the  variable  states  of  atmospheric  temperature  and 
humidity,  and  also  according  to  differences  in  the  activity  of  the 
circulation.  The  only  satisfactory  information  we  can  hope  to 
attain  is,  as  to  the  aggregate  loss  by  exhalation  from  the  skin  and 

*  [MM.  Breschet  and  Roussel  de  Vauzeme  have  described  an  apparatus  in 
the  skin  for  the  secretion  of  the  sweat,  consisting  of  a  glandular  parenchyma, 
which  secretes,  and  of  ducts,  which  pour  the  secreted  humour  on  the  surface 
of  the  body.  These  ducts  are  said  to  be  arranged  spirally,  and  to  open  very 
obliquely  under  the  scales  of  the  epidermis.  To  this  apparatus  they  apply 
the  epithet  "  diapnogenous,"  and  to  the  ducts  the  epithet  "  sudoriferous"  or 
"hidrophorous."] 


EXCRETORY    FUNCTION    OF    THE    KIDNEYS.  241 

the  lungs.  The  daily  loss  of  weight  from  these  two  sources  taken 
together  is  stated  by  Haller*  to  vary  from  thirty  ounces  in  the 
colder  climates  of  Europe,  to  sixty  in  the  warmer,  and  is  estima- 
ted by  Lavoisier  and  Seguinf  at  forty-five  ounces  in  the  climate 
of  Paris.  But  this  quantity  is,  of  course,  from  the  causes  already 
mentioned,  liable  to  extreme  variation.  It  has  been  estimated 
that,  of  the  whole  quantity  thus  exhaled  from  the  skin  and  from 
the  lungs,  about  two-thirds  are  derived  from  the  former  source, 
and  one-third  from  the  latter. 


Sect.  III. — Excretory  Function  of  the  Kidneys. 

556.  A  considerable  proportion  of  fluid  is  also  carried  off  from 
the  system  by  the  kidneys  ;  the  peculiar  office  of  which,  however, 
appears  to  be  to  eliminate  more  especially  the  saline  materials, 
which  are  to  be  thrown  oft';  and,  in  particular,  the  peculiar  sub- 
stance termed  urea,  which,  as  we  have  already  remarked >  par- 
takes much  of  the  character  of  resinous  bodies.  As  urea  contains 
a  very  large  proportion  of  nitrogen,  it  is  probable  that  the  kidneys 
are  the  channels  provided  in  the  economy  for  the  removal  of  any 
excess  of  this  element  which  takes  place  in  the  system. 

557.  The  chemical  analysis  of  the  urine  has  engaged  the  at- 
tention of  a  great  number  of  physicians  and  philosophers,  not  only 
from  its  supposed  connexion  with  various  states  of  the  body  in 
health  and  disease,  but  also  from  its  containing  a  great  multitude 
of  constituents,  some  of  which  have  very  peculiar  properties. 
Above  twenty  different  substances  have  been  detected  as  entering 
into  its  composition  ;  and  almost  every  year  is  adding  to  the  list 
of  newly  discovered  ingredients.  The  existence  of  phosphorus 
in  this  fluid  has  long  been  known  ;  and  the  urine  was,  till  lately, 
the  only  source  whence  this  elementary  substance  could  be  pro- 
cured in  any  quantity.  Scheele  discovered  the  uric  or  lithic 
acid,  which  is  one  of  the  most  remarkable  of  the  animal  products. 
The  labours  of  Fourcroy  and  Vauquehn  led  to  the  knowledge  of 
the  exact  composition  of  many  of  the  neutral  salts  contained  in 
the  urine.  This  analysis  was  carried  still  farther  by  Cruickshank 
in  England,  and  by  Proust  in  Spain,  but  has  been  brought  to  its 
present  state  of  perfection  chiefly  by  the  labours  of  BerzeliusJ  in 
Sweden. 

558.  The  daily  quantity  voided,  as  well  as  the  sensible  qualities 
of  this  secretion,  is  greatly  modified  by  circumstances.  The 
former  has  been  estimated  at  an  average  as  being  about  two  pounds 


*  Elementa  Physiologise,  xii.  2,  11. 

f  Memoires  de  1'  Academie  des  Sciences,  pour  1790,  p.  601. 
X  Annals  of  Physiology,  ii.  4-28. 
21 


242  NUTRITIVE    FUNCTIONS. 

avoirdupois.*  Its  mean  specific  gravity  has  been  fixed  at  l-03.-|- 
In  a  healthy  state  it  generally  exhibits  acid  properties,  arising 
from  the  presence  of  uncombined  phosphoric,  lactic,  uric,  benzoic, 
and  carbonic  acids.  These  acids,  together  with  the  muriatic 
and  fluoric  acids,  also  exist  in  combination  with  several .  earthy 
and  alkaline  bases,  comprising  ammonia,  lime,  magnesia,  potass, 
and  soda;  the  principal  compounds  thus  formed  being  the  phos- 
phates of  lime  and  magnesia,  ammonia  and  soda,  the  sulphates 
of  potass  and  of  soda,  the  lactate  of  ammonia,  the  muriate  of  soda, 
and  the  fluate  of  lime.  There  exist,  besides,  a  large  proportion 
of  urea  (composing  nearly  one-thirteenth  of  the  whole  quantity 
of  urine,  and  about  one-half  of  its  solid  ingredients),  mucus, 
gelatin,  albumen,  and  a  small  portion  of  the  unacidified  sulphur. 
The  presence  of  a  minute  quantity  of  silica  has  also  been  detected 
by  Berzelius,  amounting  to  about  the  220th  part  of  the  solid 
matter  contained  in  the  urine.  The  weight  of  the  solid  ingredients 
obtained  by  evaporation  is  one-fifteenth  of  the  whole  fluid,  the 
rest  being  water.  The  several  ingredients  above  mentioned 
may  each  be  rendered  evident  by  the  application  of  appropriate 
tests. 

559.  Urea  is  a  peculiar  animal  product,  which  is  procured 
from  urine  evaporated  to  the  consistence  of  a  syrup  and  allowed 
to  crystallize ;  after  which  alcohol  is  added,  which  dissolves  the 
urea,  whence  that  substance  is  obtained  by  evaporation.  It  then 
appears  in  the  form  of  crystalline  plates,  and  has  a  light  yellow 
colour,  a  smell  resembling  garlic,  and  a  strong  acrid  taste.  It  is 
chiefly  characterised  by  the  bulky  flaky  compound  which  it  forms 
with  nitric  acid.  By  distillation  it  yields  about  two-thirds  of  its 
weight  of  carbonate  of  ammonia:  and  by  spontaneous  decompo- 
sition it  is  resolved  into  ammonia  and  acetic  acid.  It  possesses 
the  very  remarkable  property  of  changing  the  form  of  ihe  crys- 
tals of  common  salt  of  muriate  of  soda,  which,  as  is  well 
known,  usually  crystallize  in  cubical  crystals  ;  but  which,  when 
mixed  with  a  small  quantity  of  urea,  assume  the  form  of  octohe- 
drons.  What  adds  to  the  singularity  of  this  effect  is,  that  its 
operation  is  precisely  the  reverse  on  muriate  of  ammonia,  or  sal 
ammoniac ;  the  ordinary  form  of  the  crystals  of  this  salt  are 
octohedrons,  but  when  urea  is  present,  they  take  the  form  of 
cubes.     Urea  contains  a  much  larger  proportion  of  nitrogen  than 

*  [The  estimates  of  observers  vary;  Boissier  states  the  average  daily 
quantity  to  be  tweniy-two  ounces;  Dr.  Thomas  Thomson  fifty-three;  and 
Lining-  from  fifty-six  to  fifty-nine  ounces.  Perhaps  the  average  in  the  text 
is  rather  too  small.] 

t  [This  is  probably  too  high.  Its  specific  gravity  of  course  varies  according 
to  circumstances.  Chossat  estimated  it  from  1.001  to  1.038;  Cruickshank 
from  1.005  to  1.033;  Prout  from  1.010  to  1.015,  Gregory  .from  1.005 
to  1.033  ;  Elliotson,  from  1.015  to  1.025;  and  Dr.  Thomas  Thomson  found 
%he  average,  during  ten  days,  to  be  1.013.     Dunglison's  Physiology,  ii.  299.] 


EXCRETORY    FUNCTION    OF    THE    LIVER.  243 

any  other  animal  principle.  This  substance  has  been  found  in 
the  blood,  after  its  separation  by  the  kidneys  has  been  prevented, 
by  the  extirpation  of  those  glands.  Berzelius  has  advanced  an 
opinion,  that  urea  is  furnished  by  the  animal  matter  of  the  sero- 
sity  of  the  blood,  from  the  similarity  of  some  of  its  properties, 
and  also  from  the  circumstance,  that  after  the  kidneys  have  been 
removed,  the  animal  matter  of  the  serosity  is  first  increased  in 
quantity,  and  afterwards  assumes  the  character  of  urea.  It 
appears  probable  that  the  principal  function  of  the  kidney  is  the 
separation  from  the  blood  of  the  excess  of  nitrogen  which  it 
may  contain,  and  its  excretion  in  the  form  of  urea  ;  thus  per- 
forming an  operation  with  respect  to  this  element  analogous  to 
that  of  the  lungs  with  regard  to  the  superfluous  carbon  of  the 
blood.* 


Sect.  IV. — Excretory  Function  of  the  Liver. 

560.  Cholesterine,  or  the  peculiar  matter  found  in  the  bile,  and 
which  composes  about  eight  per  cent,  of  that  fluid,  contains  a 
large  proportion  of  nitrogen.  Whatever  may  be  its  uses  in  con- 
tributing to  the  formation  of  chyle,  it  is  ultimately  rejected  from 
the  body,  and  may  therefore  be  classed  among  the  excrementi- 
tious  substances.  We  have  already  noticed  the  singular  circum^ 
stance  regarding  the  mode  of  its  preparation,  in  being  formed 
from  venous  instead  of  arterial  blood,  as  is  the  case  with  all  the 
other  known  secretions. 

561.  It  is  doubtful  how  far  these  two  peculiar  substances,  urea 
and  cholesterine,  may  be  considered  as  pre-existing  in  the  blood, 
or  as  formed  by  the  organs  which  respectively  secrete  them.  It 
has  been  ascertained  by  the  experiments  of  Prevost  and  Dumas, 
that  in  animals  in  whom  the  secretion  of  urine  is  suppressed  by 
the  removal  of  the  kidneys,  urea  may,  after  some  time,  be 
detected  in  the  blood ;  and  Dr.  Bostock  ascertained  that  a  simi- 
lar substance  makes  its  appearance  in  the  human  blood,  in  cases 
where  the  secretion  of  urine  had  been  much  obstructed  by  disease 
of  the  kidneys.  The  secretion  from  the  liver  is  not  liable  to  so 
much  variation  in  its  amount,  as  that  from  the  other  excernent 
organs;  it  is,  however,  diminished  during  febrile  excitement  and 
inflammatory  conditions  of  the  circulation,  and  increased  by 
moderate  exercise,  and  by  external  warmth.  Both  the  liver  and 
the  kidneys,  accordingly,  may  be  ranked  among  the  compensa- 
ting organs,  or  those  which  have  their  actions  occasionally 
increased  in  order  to  supply  deficiencies  in  the  functions  of 
others.     The  excretion  of  watery  fluid  from  the  skin  and  lungs 

*  See  Berard,  Annales  de  Chemie  et  de  Physique,  v.  296. 


244  NUTRITIVE    FUNCTIONS. 

is  evidently  made  to  alternate  with  that  fron:i  the  kidneys,  each 
of  these  organs  being  capable  of  occasionally  supplying  the 
office  of  the  others.  The  chemical  properties  of  the  urine  are 
very  much  influenced  by  the  condition  of  the  digestive  functions. 
But  the  necessity  of  the  excretion  of  urea  is  apparent  from  the 
rapidly  fatal  consequences  which  ensue  from  its  accumulation 
in  the  system,  when  the  secretion  from  the  kidneys  is  suppressed, 
and  which  would  lead  to  the  conclusion,  that  this  substance,  when 
present  in  sufficient  quantity,  speedily  acts  on  the  nervous  sys- 
tem as  a  virulent  poison. 


CHAPTER   XIII. 

NUTRITION. 

562.  Nutrition  consists  in  the  ayjpropriation  of  the  materials 
furnished  by  the  blood  in  the  course  of  circulation,  and  modified 
by  the  processes  of  secretion,  to  the  purposes  of  growth,  and  to 
the  repair  of  that  waste  which  is  continually  experienced  by  the 
solid  structures  of  the  body,  in  consequence  of  the  exercise  of 
their  respective  offices.  We  understand  as  little  what  are  the 
particular  processes  by  which  these  purposes  are  accomplished 
as  we  do  respecting  those  of  secretion.  No  mechanical  or 
chemical  hypothesis  which  can  be  devised  appears  at  all  ade- 
quate to  the  solution  of  this  mysterious  problem.  The  analogy 
of  crystallization,  implied  in  the  celebrated  definitions  of  Linnasus, 
in  which  the  three  kingdoms  of  nature  are  contrasted,  is,  in  a 
philosophical  point  of  view,  utterly  fallacious.  According  to 
this  great  naturalist,  "  minerals  grow,  vegetables  grow  and  live, 
animals  grow,  live,  and  feel."  It  requires  no  lengthened  argu- 
ment to  show  that  the  growth  of  an  animal,  or  of  a  plant,  is  a 
phenomenon  belonging  to  a  class  entirely  different  from  the 
increase  of  a  mineral  body.  The  latter  is  effected  \)y  the  succes- 
sive accretion  of  new  layers  of  materials,  which  merely  augment 
the  volume  of  the  body,  without  adding  to  it  any  new  properly; 
so  that  the  separation  of  its  parts  destroys  only  the  form  of  the 
aggregate,  and  not  any  of  its  essential  qualities.  But  organized 
bodies  are  nourished  from  internal  resources,  and  the  materials 
which  are  incorporated  with  their  substance  have  undergone  a 
slow  and  gradual  elaboration  in  the  organs  themselves,  and  have 
been  assimilated  to  the  qualities  of  the  body  of  which  they  are 
to  form  a  component  part.  We  may  consider  them  as  the  result 
of  the  operation  of  the  organic  affinities,  to  which  we  have 
already  referred  the  phenomena  of  secretion. 


OSSIFICATION.  245 

563.  The  only  general  fact  of  importance  which  has  been  es- 
tablished with  regard  to  the  succession  of  phenomena  in  this  func- 
tion, is,  that  the  enlargement  of  any  organ  appears  to  depend  es- 
sentially on  the  state  of  the  circulation,  in  that  part,  and  on  the 
supply  of  blood  by  its  arteries.  The  increased  growth  of  a  part 
at  any  period,  compared  with  that  of  neighbouring  parts,  is  always 
preceded  and  accompanied  by  a  marked  enlargement  of  the 
arteries  which  furnish  it  with  blood  ;  and  this  is  invariably  obser- 
ved, whether  that  growth  be  natural  or  morbid.  A  theory  has 
been  advanced,  that  nutrition  is  effected  by  the  direct  union  of 
the  red  particles  of  the  blood,  or  of  their  nuclei,  with  the  tissues. 
This  theory  is  successfully  combated  by  Miiller.* 

564.  Although  we  are  unable  to  trace  the  exact  nature  of  the 
processes  of  nutrition,  yet  much  curious  information  may  be  col- 
lected by  observing  the  succession  of  phenomena  in  the  case  of 
the  formation  of  particular  structures.  Those,  which  we  shall 
select  for  the  purpose  of  illustration,  are  the  bones  and  the  teeth, 
in  which  the  several  stages  of  growth  admit  of  being  observed. 


Sect.  I. — Ossification. 


565.  The  process  of  ossification  is  particularly  interesting,  from 
its  exhibiting  the  operations  of  nature  in  the  completion  of  an  ela- 
borate structure  of  such  great  importance  in  its  mechanical  rela- 
tions to  the  system,  as  the  osseous  fabric.  In  the  early  periods 
of  the  foetal  state,  we  can  but  just  trace  the  figures  of  some  of  the 
larger  bones,  which  appear  to  be  modelled  in  a  soft  gelatinous 
matter  contained  in  a  delicate  membrane.  This  substance,  as 
well  as  its  membrane,  acquires  greater  density,  and  the  form 
assumes  more  the  appearance  of  cartilage.  In  process  of  time, 
opaque  white  spots  are  perceived  on  different  parts  of  its  surface, 
which,  when  examined  by  the  microscope,  exhibit  a  fibrous  appear- 
ance. These  lines  increase  in  number  and  extent ;  and,  after  a  time, 
red  points  are  seen  dispersed  throughout  the  future  bone,  in  conse- 
quence of  the  enlargement  of  the  vessels  which  now  admit  the  red 
globules  of  the  blood.  Soon  after  this,  we  find  the  earthy  matter 
deposited  in  great  abundance,  imparting  hardness  and  rigidity  to 
the  structure.  In  the  long  bones  of  the  extremities,  the  osseous 
substance  forms  at  first  a  short  hollow  cylinder,  as  if  it  were 
deposited  from  the  vessels  of  the  investing  membrane,  or  perios- 
teum. In  the  flat  bones  of  the  cranium,  ossification  commences 
froni  a  few  central  points,  and  spreads  on  all  sides,  the  fibres 
taking  a  radiating  direction.  In  proportion  as  the  bony  material 
extends,  the  cartilage  is  removed  by  the  absorbent  vessels,  in  order 

•  Elements  of  Physiology,  translated  by  Baly,  p.  359. 
21* 


246  NUTRITIVE    FUNCTIONS. 

to  make  room  for  the  extension  of  the  bone.  After  a  certain 
time,  in  the  cylindrical  bones,  a  cavity  is  formed  in  the  middle,  in 
consequence  of  the  absorption  of  central  portions  of  cartilages  and 
of  bone  which  had  occupied  that  situation.  These  two  opposite  pro- 
cesses of  absorption  and  deposition  continue  during  the  whole  of 
the  future  growth  of  the  bone,  the  interior  parts  being  removed  in 
proportion  as  fresh  bony  layers  are  added  at  the  exterior  surface. 
Thus,  when  the  outer  part  of  the  bone  is  compact  and  hard,  the 
interior  is  either  formed  into  a  complete  cavity,  or  into  the  can- 
cellated structure  formerly  described. 

566.  Such  are  the  few  well  ascertained  known  facts  relative 
to  ossification  ;  but  numberless  have  been  the  speculations  to 

^  which  they  have  given  rise.  Most  of  the  opinions  of  the  ancients 
on  this  subject  were  extremely  vague  and  hypothetical,  and  have 
been  fully  refuted  by  modern  physiologists.  Many  of  the  hypo- 
theses of  the  latter  have  undergone  a  similar  fate.  The  one 
which  has  acquired  most  celebrity  is  that  of  Duhamel,  who,  fol- 
lowing the  analogy  of  the  growth  of  trees,  conceived  that  the 
bones  were  formed  of  concentric  rings,  or  laminae,  deposited 
from  the  periosteum.  He  endeavoured  to  adduce  in  support  of 
his  theory  the  results  of  experim.ents  in  which  bones  acquired  a 
red  tinge,  when  madder  vufes  given  with  the  food.  He  alleged 
that  when  the  madder  wew  occasionally  intermitted,  and  again 
resumed,  many  times  in  succession,  the  bones  of  the  animal  ex- 
hibited alternate  rings  of  a  red  and  white  colour,  corresponding 
to  the  periods  when  the  animal  had  taken  madder,  and  had  in- 
termitted it.  It  has  since  been  shown,  however,  that  his  ima- 
gination in  this  instance  must  have  misled  him  ;  for  no  such  result 
takes  place  under  the  circumstances  he  describes, 

567.  The  reparation  of  fractured  bones  by  the  powers  of  the 
constitution  is  a  striking  instance  of  the  beautiful  provisions  of 
nature  for  remedying  injuries  accidentally  occurring  to  the  body. 
The  fractured  ends  are  quickly  united  by  li  bony  substance  called 
callus,  formed  in  a  manner  very  similar  to  that  by  which  the 
bone  itself  is  originally  constructed.  The  arteries  near  the  seat 
of  the  injury  pour  out  a  kind  of  lymph,  which  coagulates,  and  is 
either  gradually  converted  into  cartilage,  or  replaced  by  carti- 
lage after  it  has  itself  been  absorbed.  The  deposition  of  phosphate 
of  hme  then  takes  place  within  this  cartilage,  which  is  either  re- 
moved or  adapted  to  its  reception,  and  thus  the  ends  of  the  bone 
are  cemented  together,  and  the  limb  rendered  as  firm  as  before 
the  accident. 

Sect.  II. — Dentition. 

568.  No  less  curious  and  interesting  is  the  process  employed 
in  the  formation  of  the  teeth.  The  rudiments  of  every  tooth, 
when  examined  in  the  foetus,  consists  of  a  gelatinous  pulp,  which 


NUTRITION    OF    THE    SQFTER    TEXTURES.  247 

is  extremely  vascular,  enclosed  in  a'  double  investment  of  mem- 
brane. The  outer  membrane  is  soft  and  spongy,  and  is  appa- 
rently destitute  of  vessels ;  while  the  inner  one  is  firmer,  and 
extremely  vascular.  The  first  depositions  are  those  of  bony 
matter,  which  take  place  on  the  exterior  surface  of  the  vascular 
pulp,  and  chiefly  on  the  upper  part,  but  within  the  membranous 
coverings  already  noticed.  The  shell  of  bone  thus  formed  has 
the  shape  of  the  future  tooth,  and  acquires  thickness  from  suc- 
cessive deposits  of  bone  in  its  inner  surface,  which  are  still  made 
by  the  outer  surface  of  the  vascular  pulp.  When  the  ossification 
is  sufficiently  advanced,  the  pulp  which  has  thus  served  as  a 
mould  for  the  tooth,  divides  itself  into  two  or  more  parts,  cor- 
responding to  the  intended  number  of  fangs,  so  that  the  ossific 
matter  is  now  deposited  in  the  form  of  as  many  tubes  round  these 
portions  of  the  pulp,  and  growing  in  a  direction  towards  the  jaw, 
forces  the  tooth  in  the  contrary  direction ;  thus  ip  the  lower  jaw 
the  tooth  rises,  and  in  the  upper  jaw  it  descends.  The  enamel  is 
deposited  after  the  body  of  the  tooth  is  considerably  advanced  in 
its  formation.  It  is  the  product  of  a  secretion  from  the  inner 
surface  of  the  outermost  of  the  two  membranes,  which  form  the 
capsule  of  the  tooth,  and  the  materials  deposited  from  it  adhere 
strongly  to  the  bony  crown  of  the  tooth  which  they  surround. 
This  secreting  capsule  has  been  called  the  chorion  by  Herissant, 
who  has  given  an  accurate  description  of  the  process  of  denti- 
tion. Layer  after  layer  of  enamel  is  thus  deposited,  till  the 
growth  of  that  part  of  the  tooth  has  been  completed  ;  then  the 
chorion  shrivels  and  is  absorbed,  and  the  tooth  still  continuing  to 
grow  at  the  root,  pierces  the  gum,  the  resistance  of  which  has 
been  gradually  diminishing  by  the  absorption  of  its  substance. 


Sect.  III. — Nutrition  of  the  Softer  Textures. 

569.  Greater  difficulty  exists  in  following  the  succession  of 
changes  which  attend  the  growth  and  nutrition  of  the  softer 
textures,  than  of  those  we  have  now  considered,  because  the  ma- 
terials employed  in  their  construction  are  less  distinguishable  by 
the  eye  from  the  other  animal  substances,  and  their  changes  are 
less  easily  traced,  than  those  exhibited  by  the  calcareous  deposits 
of  the  osseous  fabric. 

A  question  here  presents  itself,  of  great  importance  with  rela- 
tion to  our  knowledge  of  the  nature  of  the  vital  powers,  but  of 
which  the  solution  is  attended  with  the  greatest  difficulties.  It 
is  this  :  how^  far,  it  may  be  asked,  are  the  powers  of  secretion 
exerted  in  merely  separating  from  the  blood  those  organic  pro- 
ducts which  are  already  contained  as  ingredients  of  that  fluid, 
and  how  far  do  they  also  extend  to  the  actual  formation  of  new 


248  NUTRITIVE    FUNCTIONS. 

1 

proximate  elements;  and  next,  what  reason  is  there  to  believe 
that  the  vital  powers  are  capable  of  producing,  from  the  mate- 
rials presented  to  them,  originally  derived  from  the  food,  or  the 
atmosphere,  any  quantity  of  those  chemical  substances,  which, 
never  having  hitherto  been  decomposed,  must,  in  the  present 
state  of  the  science,  be  regarded  as  elementary? 

The  consideration  of  the  chemical  analysis  of  the  blood,  and 
of  the  substances  prepared  from  it  will  suffice  to  show  that  most, 
if  not  all  the  secretions,  may  very  possibly  be  produced  solely 
by  the  operation  of  ordinary  chemical  affinities.  It  has  been 
found,  indeed,  that  we  are  able,  by  certain  chemical  processes, 
to  form  from  the  blood,  out  of  the  body,  substances  similar  to 
many  of  the  secretions;  and  we  are  therefore  warranted  in  the 
supposition  that  operations  of  the  same  kind  are  carried  on  by 
the  secreting  organs  within  the  body.  It  is  interestng,  however, 
to  trace  the  orig,in  of  many  of  the  products  of  the  secretion,  from 
the  ingredients  contained  in  the  blood  itself.  On  this  subject 
Muller*'  remarks,  that  some  of  the  proximate  elements  of  the 
tissues  exist  in  part  ready  formed  in  the  blood.  The  albumen 
which  enters  into  the  composition  of  the  brain  and  glands,  and 
of  many  other  structures,  in  a  more  or  less  modified  state,  is 
contained  in  the  blood ;  the  fibrin  of  the  muscles  and  muscular 
structures  is  the  coagulable  matter  dissolved  in  the  lymph  and 
blood ;  the  fatty  matter,  which  contains  no  nitrogen,  exists  in  a 
free  state  in  the  chyle;  the  azotised  and  phosphoretted  fatty 
matter  of  the  brain  and  nerves  exists  in  the  blood  combined  with 
the  fibrin,  albumen,  and  cruorin.  The  iron  of  the  hair,  pigmen- 
tum  nigrum,  and  crystalline  lens,  is  also  contained  in  the  blood; 
the  silica  and  manganese  of  the  hair,  and  the  fluor  and  calcium 
of  the  bones  and  of  the  teeth,  have  not  hitherto  been  detected  in 
the  blood,  probably  from  their  existing  in  it  in  but  very  small 
proportion.  The'  matters  here  enumerated  are  attracted  from 
the  blood  by  particles  of  the  organs  analogous  to  themselves, 
partly  in  the  state  .in  which  they  afterwards  exist  in  the  organs ; 
in  other  instances,  their  ultimate  elements  are  newly  combined 
in  them,  so  as  to  form  new  proximate  principles;  for  the  opinion 
that  all  the  component  elements  of  the  organs  exist  previously  in 
the  blood  in  their  perfect  state,  cannot  possibly  be  adopted  ;  the 
components  of  most  tissues  in  fact  present,  besides  many  modifi- 
cations of  fibrin,  albumen,  fat,  and  osmazome,  other  perfectly 
peculiar  matters,  such  as  the  gelatin  of  the  bones,  tendons,  and 
cartilages,  nothing  analogous  to  which  is  contained  in  the  blood. 
The  substance  of  the  vascular  tissue,  and  also  the  different  glan- 
dular substances,  cannot  be  referred  to  any  of  the  simple  compo- 
nents of  the  blood.     Even  the  fibrin  of  muscle  cannot  be  consi- 

*  Physiology,  &c.  p.  361. 


GENERAL  PHENOMENA  OP  NUTRITION. 


249 


dered  as  exactly  identical  with  the  fibrin  of  the  liquor  sanguinis. 
Between  coagulated  fibrin  and  coagulated  albumen,  there  is 
scarcely  any  chemical  difl^erence,  except  in  their  action  on 
peroxide  of  hydrogen;  the  only  very  important  distinction  be- 
tween the  fibrin  dissolved  in  the  blood  and  the  albumen  is,  that 
the  former  coagulates  as  soon  as  it  is  withdrawn  from  the 
animal  body,  while  the  latter  does  not  coagulate  spontaneously, 
but  requires  a  heat  of  from  158°  to  167°  Fahr.,  or  some  chemical 
agents,  such  as  acids,  concentrated  solutions  of  fixed  alkali,  or 
metallic  salts ;  and  the  fibrin  of  muscle  in  its  chemical  characters 
has  scarcely  a  greater  analoijy  with  coagulated  fibrin,  than  with 
coagulated  albumen.  In  its  vital  properties  the  fibrin  of  muscle 
differs  from  both.  The  comparison  of  nervous  substance,  again, 
with  the  fatty  matter  containing  nitrogen  and  phosphorus,  is  only 
justified  by  the  present  imperfect  state  of  organic  chemistry. 

The  blood,  as  Dr.  Bostock*  observes,  is  a  substance,  the  com- 
position of  which  is  peculiarly  well  adapted  to  undergo  the  change 
necessary  for  the  processes  both  of  secretion  and  of  nutrition,  as 
it  consists  of  a  number  of  ingredients,  which  are  held  together  by 
a  weak  affinity,  liable  to  be  disturbed  by  a  variety  even  of  what 
might  appear  the  slightest  causes.  As  examples  of  the  facility 
with  which  these  changes  may  be  effected,  we  may  cite  the 
numerous  reagents  which  have  the  power  of  coagulating  albumen; 
the  action  upon  it  and  upon  fibrin  of  dilute  nitric  acid,  which 
converts  these  substances  respectively  into  adipose  matter  and 
jelly,  changes  which  are  probably  the  result  of  the  addition  of 
oxygen  to  the  fibrin  and  to  the  albumen ;  and  there  is  some  reason 
to  believe  that  by  applying  the  same  reagent  to  the  red  particles, 
we  may  obtain  a  substance  nearly  resembling  bile. 

With  regard  to  the  formation  of  the  saline  secretions,!  and  of 
those  substances,  the  elements  of  which  are  not  to  be  found  in 
the  blood,  or  at  least  not  in  sufiicient  quantity  to  account  for  the 
great  accumulation  that  takes  place  in  certain  parts  of  the  system, 
and  of  which  the  source  is  not  apparent,  we  must  confess  that 
the  present  state  of  the  science  aitords  no  means  of  explaining 
the  phenomena.  "  To  suppose,"  as  Dr.  Bostock  justly  remarks, 
"  that  we  are  affording  any  real  explanation  by  ascribing  it  to  the 
operation  of  the  vital  principle,  or  to  any  vital  affinities,  which 
is  merely  a  less  simple  mode  of  expressing  the  fact,  is  one  ot 
those  delusive  attempts  to  substitute  words  for  ideas,  which  have 
so  much  tended  to  retard  the  progress  of  physiological  science." 

Sect.  IV. — General  Phenomena  of  Nutrition. 
570.  The  instances    we  have  above  given  of  the   processes 

*  Elementary  System  of  Physiology,  p.  518.  t  ^^^^-  P-  ^32. 


250  NUTRITIVE    FUNCTIONS. 

employed  in  ossification  and  dentition,  together  with  the  varied 
operations  concerned  in  the  formation  and  nutrition  of  all  the 
softer  textures  of  the  body,  forcibly  illustrate  the  beneficent  care 
displayed  in  the  construction  of  every  part  of  the  frame,  and  the 
admirable  adjustment  of  the  long  series  of  means  which  have 
been  provided  for  the  attainment  of  these  diversified  and  fre- 
quently remote  objects  of  the  animal  economy.  Every  part 
undergoes  a  continued  and  progressive  change  of  the  parti- 
cles which  compose  it,  even  though  it  remain  to  all  outward 
appearance  the  same.  The  materials  which  had  been  united 
together  by  the  powers  of  nutrition,  and  fashioned  into  the  several 
organs,  are  themselves  severally  and  successively  removed  and 
replaced  by  others,  which  again  are  in  their  turn  discarded,  and 
new  ones  substituted  in  their  place,  until,  in  process  of  time, 
scarcely  any  portion  of  the  substance  originally  constituting  the 
organs  remains  as  their  component  part. 

571.  We  see  from  the  examples  of  the  bones,  that  this  con- 
tinual renovation  of  the  materials  of  the  body  takes  place  in  the 
most  solid,  as  well  as  in  the  softest  textures;  and  so  great  is  the 
total  amount  of  these  changes,  that  doubts  may  reasonably  be 
entertained  as  to  the  identity  of  any  part  of  the  body  at  different 
epochs  of  its  existence.  The  ancients  assigned  a  period  of  seven 
years  as  the  time  required  for  the  complete  renovation  of  all 
the  materials  of  the  system,  but  perhaps  this  entire  change  may 
take  place  during  a  shorter  interval.* 

572.  The  two  functions  we  have  been  considering,  namely, 
nutrition  and  absorption,  may  be  regarded  as  antagonist  powers, 
each  continually  counteracting  the  effects  of  the  other.  In  the 
early  periods  of  life,  though  both  are  in  full  activity,  the  former 
predominates ;  all  the  organs  enlarging  in  their  dimensions  by  the 
addition  of  fresh  materials  in  greater  quantity  than  the  losses  by 
absorption,  the  whole  body  is  in  a  state  of  growth.  In  the  course 
of  time,  the  frame  having  attained  its  prescribed  dimensions, 
these  opposite  processes  of  reparation  and  decay  approach  nearer 
to  an  equality  ;  and  at  length  are  exactly  balanced.  The  parts 
then  cease  to  grow,  and  the  system  may  be  said  to  have  reached 
its  state  of  maturity.  This  is  the  condition  of  the  adult,  in  which 
the  equilibi'ium  of  the  functions  is  maintained  for  a  great  num- 
ber of  years.  At  length,  however,  the  period  arrives  when 
the  balance,  hitherto  so  evenly  kept,  begins  to  incline,  the  reno- 
vating powers  of  the  system  are  less  equal  to  the  demands  made 
upon  them,  and  the  waste  of  the  body  exceeds  the  supply.  It 
contracts  in  its  dimensions ;  it  has  attained  its  period  of  declen- 
sion, which  marks  the  progress  of  age,  and  ultimately  leads  to 

*  See  the  Article  Age,  in  the  Cyclopaedia  of  Practical  Medicine,  vol.  i. 
p.  34. 


SENSORIAL    FUNCTIONS — GENERAL    VIEWS.  251 

decrepitude.  The  fabric  then  betrays  unequivocal  symptoms 
of  decay,  the  functions  are  imperfectly  performed,  the  vigour  of 
the  circulation  flags,  the  flame  flickers  in  the  socket,  and  is  finally 
extinguished  in  death.  Thus  is  the  whole  duration  of  life,  from 
the  first  development  of  the  germ  to  the  period  of  its  dissolu- 
tion, occupied  by  a  series  of  actions  and  reactions,  perpetually 
varying,  yet  constantly  tending  to  definite  and  salutary  ends. 

573.  We  have  now  concluded  the  account  we  proposed  to 
give  of  the  long  series  of  functions  which  maintain  the  various 
organs  of  the  system  in  that  mechanical  condition  and  chemical 
composition  fitting  them  for  the  exercise  of  their  several  offices 
in  the  economy.  We  have  next  to  enter  into  the  consideration 
of  the  higher  order  of  functions  connected  with  the  nervous  sys- 
tem. 


CHAPTER    XIV. 


THE  SENSORIAL  FUNCTIONS. 

Sect.  I. — -General  Views. 

574.  The  functions  we  have  hitherto  considered,  however 
admirably  contrived,  and  beautifully  adjusted,  are  calculated 
only  for  the  maintenance  of  a  simply  vital  existence.  All  that 
is  obtained  by  their  means  is  a  mass  of  organized  materials,  which 
lives,  which  is  nourished,  which  grov/s,  which  declines,  and  which 
perishes  in  a  certain  definite  period,  by  its  mere  internal  mecha- 
nism. But  these  can  never  be  the  real  ends  of  animal  existence. 
Sensation,  voluntary  motion,  pleasure  and  pain,  together  with  all 
the  intellectual  operations  to  which  they  lead,  these  must  be  the 
proper  objects  of  animal  life;  these  the  purposes  for  which  the 
animal  was  created.  In  man  we  find  the  extension  of  these 
latter  faculties  to  an  extraordinary  degree,  and  the  addition  of 
moral  attributes  which  elevate  him  so  far  above  the  brute  crea- 
tion, and  place  him  one  step  nearer  to  that  divine  essence  after 
whose  likeness  he  was  made. 

575.  The  functions  of  sensation,  of  voluntary  motion,  and  of 
thought,  are  those  which  establish  our  mental  connexions  with 
the  external  world;  which  enable  us  to  acquire  a  knowledge  of 
the  existence  and  properties  of  the  material  objects  that  surround 
us  ;  which  awaken  in  us  the  operations  of  our  own  minds ;  which 


252  SENSORIAL   FUNCTIONS. 

bring  us  in  communication  with  other  intellectual  and  sentient 
beings,  and  which  enable  us  to  react  on  matter,  to  exercise  over 
it  the  dominion  of  the  will,  and  to  influence  the  condition  of  those 
other  beings  which  like  us  have  received  the  gift  of  hfe,  of  sen- 
sation, and  of  intellect. 

576.  Throughout  the  whole  of  the  inquiries  in  which  we  are 
about  to  engage  it  is  important  to  keep  steadily  in  view  the 
essential  and  fundamental  distinction  between  mind  and  matter. 
Of  the  existence  of  our  own  sensations,  ideas,  thoughts,  and  voli- 
tions, we  have  the  highest  degree  of  evidence  that  human  know- 
ledge can  admit  of, — that  of  our  own  consciousness.  Of  the 
existence  of  matter,  that  is,  of  causes  foreign  to  our  own  mind, 
but  acting  on  it,  and  giving  rise  to  sensations,  which  are  strictly 
mental  affections,  we  have  merely  a  strong  presumption ;  still, 
however,  the  belief  in  the  existence  of  those  causes,  however 
irresistibly  it  may  operate  in  producing  in  us  convictions,  and  in- 
fluencing our  actions,  is  yet  but  an  inference  from  the  regularity 
in  the  succession  of  our  sensations.  We  are  not  justified  in 
saying  that  it  is  impossible  we  can  be  deceived  in  this  belief; 
whereas  in  the  consciousness  of  our  mental  existence  we  can- 
not possibly  be  mistaken,  because  that  consciousness  implies  the 
very  fact  of  our  existence. 

577.  It  is,  however,  most  true,  that  notwithstanding  our  ideas 
of  mind  and  matter  are  such  as  wholly  to  exclude  our  conceiving 
any  property  to  belong  to  both  of  them  in  common ;  yet  some 
inscrutable  link  of  connexion  has,  in  our  present  state  of  exist- 
ence, been  established  between  them,  so  that  each  may,  under 
certain  circumstances,  be  affected  by  the  other.  External  matter 
acts  on  our  bodily  organs,  which  are  still  mere  matter;  but 
our  bodily  organs  act  on  our  minds  ;  and  our  minds  in  turn  react 
on  our  bodily  organs,  and  occasion  movements  which  enable  us 
to  act  on  extraneous  objects.  Moreover,  it  is  impossible  for  us 
ifi  our  present  state  to  carry  on  any  intellectual  operation,  but  by 
the  instrumentality  of  our  material  organs  ;  we  can  neither  feel, 
nor  think,  nor  will,  without  the  healthy  condition  of  the  brain, 
and  all  the  other  physical  conditions  which  such  a  state  implies. 
Disturbance  of  the  physiological  functions  of  the  brain  is  invari- 
ably attended  by  a  disturbance  of  the  mental  operations  connected 
with  those  functions.  Both  are  excited  by  certain  states  of  the 
circulation  in  the  brain  ;  both  are  instantly  suspended  by  pressure 
upon  that  organ ;  both  are  restored  by  the  removal  of  the  pres- 
sure, or  other  disturbing  cause. 

578.  The  nervous  system  is  the  name  given  to  that  assemblage 
of  organs  which  perform  the  important  functions  of  which  we 
are  now  speaking.  The  primary  office  of  the  fibres  composing 
that  system  appears  to  be  to  transmit  certain  affections,  which 
we  may  call  impressions,  from  one  part  of  that  system  to  another ; 


SENSORIAL    FUNCTIONS — GENERAL    VIEWS.  253 

and  more  particularly  to  convey  thenn  both  to  and  from  that 
particular  part  of  the  brain,  the  aflbctions  of  which  give  rise  to 
sensation,  and  accompany  our  mental  operations.  In  the  one 
case,  the  impression  made  on  one  extremity  of  a  nervous  fibril, 
adapted  to  receive  such  impression,  in  a  part  called  an  organ 
of  sense,  is  propagated  to  the  part  of  the  brain  above  described, 
and  to  which  the  name  of  sevsorium  has  been  given,  and 
thereby  producing  a  certain  physical  effect,  the  nature  ^f 
which  is  wholly  unknown  ;  sensation,  which  is  a  mental  effect, 
ensues.  In  another  case,  the  fibres  of  the  brain  are  by  their  ac- 
tion instrumental  in  retracing,  in  combining,  in  modifying  these 
impressions,  and  forming  them  into  ideas,  which  are  linked  to- 
gether by  the  laws  of  association.  Again,  the  mental  act  we 
term  volition,  and  of  which  we  are  always  conscious,  affects 
some  particular  fibres  or  portion  of  the  sensorium,  the  impres- 
sion made  upon  which  is  followed  by  an  affection  of  certain 
nervous  filaments  proceeding  from  those  parts  of  the  brain,  and 
conveying  an  influence,  (which  for  want  of  a  more  specific  term 
we  may  also  call  irritation)  to  the  muscles  in  which  these  nerves 
terminate;  and  this  is  immediately  follow^ed  by  the  contraction 
of  those  muscles.     This  constitutes  voluntary  motion. 

579.  But  the  office  of  the  nerves  extends  yet  farther.  Various 
muscles  subservient  to  many  of  the  vital  functions,  such  as  tlie 
heart,  the  stomach,  and  the  intestines,  act  without  any  interfer- 
ence, or  even  control  of  the  will.  They  compose  the  class  of 
involuntauj  muscles ;  yet  these  muscles  are  supplied  with  nerves, 
and  have  a  certain  dependence  on  the  nervous  system,  which  is 
of  a  very  peculiar  kind,  and  will  be  considered  afterwards.  These 
nerves  supplying  the  involuntary  muscles,  appear  to  have  the 
office  of  establishing  connexions  between  the  actions  of  these 
muscles,  and  of  uniting  the  various  organs  of  the  different  func- 
tions into  one  connected  harmonious  whole. 

580.  Thus  the  various  phenomena  which  relate  to  the  nervous 
system  in  the  performance  of  the  functions  we  are  considering, 
will  arrange  themselves  under  the  following  heads,  according  to 
the  natural  order  of  their  sequence  : 

First,  the  impressions  made  by  external  objects  on  the  sentient 
extremities  of  the  nerves  distributed  to  the  organs  of  sense,  through 
the  medium  of  those  organs.  Secondly,  the  transmission  of  the 
impressions  so  made  to  the  sensorium,  through  the  medium  of  the 
nerves  of  sensation.  Thirdly,  the  physical  changes  made  on  the 
sensorium.  Fourthly,  the  mental  change  consequent  on  this  phy- 
sical change  in  the  sensorium  ;  which  mental  change  is  termed 
sensation  ;  and  in  experiencing  which  the  mind  is  wholly  passive. 
Fifthly,  the  recurrence,  associations,  and  combinations  of  the 
phvsical  changes  originally  induced  in  the  sensorium,  but  probably 

22 


254  SENSORIAL    FUNCTIONS. 

extended  through  various  parts  of  the  substance  of  the  brain,  and 
simultaneous  with  various  mental  operations,  in  exercising  which 
the  mind  is  partly  passive  and  partly  active.  Sixthly,  the  mental 
act  denominated  volition,  which  is  accompanied  with  conscious- 
ness, and  in  which  the  mind  is  wholly  active.  Seventhly,  the 
corresponding  change  induced  by  volition  on  the  sensorium,  or 
origin  of  the  nerves  of  voluntary  motion.  Eighthly,  the  trans- 
mission of  the  impression  so  received  by  the  nerves  of  voluntary 
motion,  to  the  muscles  on  which  they  are  distributed.  Ninthly, 
the  contractions  of  these  muscles,  constituting  voluntary  motion^ 
Tenthly,  the  influence  of  the  nerves  on  the  muscles  of  involuntary 
motion,  and  on  various  functions  apparently  depending  on  invo- 
hmtary  actions.* 


Sect.  II. — Organization  of  the  Nervous  System. 

581.  The  nervous  system  comprises  organs  of  a  curious  and 
complicated  structure,  and  which  are  of  the  highest  importance 
in  the  animal  economy.  Their  study  is  exceedingly  interesting, 
whether  they  be  viewed  as  instruments  of  sensation,  as  sources 
of  action,  or  as  the  medium  of  connexion  between  the  body  and 
the  mind.  This  system  is  composed  of  a  considerable  mass  of 
a  soft  pulpy  substance  called  the  brain,  which  occupies  the  cavity 
of  the  skull;  a  prolongation  of  this  substance  filling  the  canal  of 
the  spine,  and  called  the  spinal  cord,  or  spinal  marrow ;  and 
of  various  processes  in  the  form  of  cords,  called  nerves,  which 
extend  from  the  brain  and  spinal  cord,  to  almost  all  parts  of  the 
body.  There  are  found  also  interspersed  in  various  parts  along 
the  course  of  the  nerves,  small  rounded  or  flattened  bodies,  called 
ganglia,  which  also  belong  to  this  system  of  organs.  All  the 
parts  of  this  system  are  intimately  related  to  each  other,  and 
although  they  differ  considerably  in  their  general  appearance, 
they  possess  many  characters  in  common.  In  point  of  structure 
they  present  us  with  three  different  modifications ;  the  ^rst  com- 
prehending the  substance  of  the  central  masses,  which  include 
the  brain  and  spinal  cord  ;  the  second,  the  nerves  ;  and  the  third, 
the  ganglia.  We  shall  proceed  to  consider  each  of  these  in  the 
above  order. 

1.  Organization  of  the  Brain  and  Spinal  Cord. 

582.  The  brain,  or  general  mass  which  fills  the'  cavity  of  the 
skull,  is  composed  of  a  number  of  parts  of  various  shapes,  the  par- 
ticular forms  and  dispositions  of  which  belong  properly  to  descrip- 

*  See  Bridgewater  Treatise  on  Animal  and  Vegetable  Physiology,  vol.  ii. 
p.  535,  note.     [Amer.  edit.  ii.  376.] 


ORGANIZATION    OF    THE    NEUVOUS    SYSTEM.  255 

live  anatomy.  It  will  be  sufficient  for  our  present  purpose  to  state 
that  it  is  divided  into  three  masses  distinguished  by  the  names  of 
cerebrum,  which  is  by  far  the  largest  portion,  and  which  occupies 
the  whole  of  the  upper  and  fore  part  of  the  cavity  of  the  skull ; 
cerehelhim,  or  lesser  brain,  which  is  situate  at  the  hinder  and 
lower  part  of  the  cerebrum ;  and  medulla  ohlongata,  which  lies  at 
the  central  part  of  the  base,  or  inner  surface  of  the  cerebrum, 
and  connects  it  with  the  cerebellum,  and  with  the  spinal  cord. 
All  these  parts,  as  well  as  the  spinal  cord  itself,  are  formed  of 
two  kinds  of  substance  ;  the  cineritious,  or  ash-coloured  substance, 
which  has  also  been  called  the  corizca/ substance;  and  the  white, 
or  medullary  substance.  These  two  substances  ai'e  variously 
intermixed,  sometimes  forming  strata  of  different  thickness,  and 
sometimes  the  one  enveloping  separate  portions  of  the  other,  in 
different  parts  of  the  whole  mass.  There  is  a  layer  of  cortical 
substance  placed  on  the  outside  of  the  cerebrum  ;  it  does  not 
however  form  a  smooth  uniform  plane,  but  is  moulded  into  con- 
volutions. In  the  cerebellum  there  is  a  similar  superficial  stratum 
formed  into  concentric  lamina).  The  convolutions  are  of  con- 
siderable depth ;  and  if  any  of  them  be  cut  through,  they  are 
seen  to  consist  of  both  cortical  and  niedullary  substance.  The 
cortical  forms  a  layer  of  considerable  thickness ;  and  on  looking 
attentively  on  its  divided  edge,  a  very  narrow  lamina  of  medullary 
substance  will  be  perceived  passing  through  it,  and  following  it 
through  all  its  windings.  This  fact  has  been  particularly  noticed 
by  Dr.  Baillie.  The  concentric  laminae  on  the  surface  of  the 
cerebellum,  are  composed  also  of  cortical  and  medullary  matter. 
By  this  arrangement,  the  quantity  of  cortical  substance,  as  well 
as  the  extent  of  its  surface  on  the  outer  part  of  the  brain,  is  very 
much  increased. 

583.  In  the  interior  of  the  brain  we  find  cavities  of  consider- 
able size,  termed  ventricles,  and  bodies  of  regular,  but  various 
shapes,  presenting  many  different  mixtures  of  two  species  of 
matter.  Where  these  bodies  appear,  from  their  outside,  to  be 
formed  of  cortical  substance  only,  on  cutting  into  this,  there  is 
found  a  considerable  mixture  of  medullary  matter ;  and  where 
they  seem,  from  their  outside,  to  be  formed  of  medullary  matter 
alone,  they  are  discovered,  on  dividing  them,  to  contain  some  corti- 
cal substance  in  the  interior.  Thus  there  is  no  particular  part  of  the 
brain  composed  purely  of  the  one  kind  of  substance  or  the  other; 
although  the  proportions  of  each  in  the  various  parts  may  be  very 
different.  A  similar  intermixture  of  cortical  and  medullary  mat- 
ter exists  in  the  spinal  cord ;  but  contrary  to  what  takes  place  in 
the  large  mass  of  the  brain,  the  cortical  part  is  placed  in  the 
interior,  and  is  enveloped  by  the  medullary. 

584.  The  medullary  substance  has  generally  been  considei'ed 
as  constituting  the  most  perfect  state  of  nervous  matter,  or  that 


256  SENSORIAL    FUNCTIONS. 

which  more  especially  exercises  the  functions  of  the  nervous 
system.  Some  physiologists,  on  the  contraiT,  consider  the  grey 
substance  as  the  seat  or  origin  of  nervous  power;  whilst  the 
fibres  of  the  white  substance  act  merely  the  part  of  conductors 
of  nervous  influence  from  one  part  to  another.  This  medullary 
portion  is  obviously  of  a  firm.er  consistence  than  the  cortical, 
and  contains  fewer  blood-vessels  interspersed  throughout  its  sub- 
stance. Both  the  one  and  the  other  are  almost  perfectly  homoge- 
neous in  their  appearance.  Ruysch  had  fancied  that  the  cortical 
substance  was  entirely  composed  of  blood-vessels,  connected  by 
cellular  membrane;  and  in  this  opinion  he  was  for  a  long  time 
generally  followed,  although  the  pulpy  consistence  it  exhibits  is 
scarcely  compatible  with  such  a  notion.  Malpighi  supposed  that 
he  had  detected  in  it  a  glandular  structure;  but  this  must  also  be 
regarded  as  a  mere  hypothesis,  unsupported  by  any  substantial 
evidence.  The  medullary  matter  presents  traces  of  a  fibrous 
structure ;  a  fact  which  was  first  observed  by  Malpighi,  and 
which  is  particularly  insisted  on  by  Drs.  Gall  and  Spurzheim  ; 
and  notwithstanding  the  existence  of  such  a  structure  is  denied 
by  other  eminent  anatomists,  it  appears  to  have  been  sufficiently 
established  by  the  elaborate  researches  of  Reil,  a  detailed  account 
of  which  has  been  given  by  Mr.  j\Iayo.* 

585.  Anatomists  are  far  from  being  agreed  as  to  the  minute 
and  ultimate  structure  of  nervous  matter.  De  la  Torre  asserts 
that  it  consists  of  a  mass  of  innumerable  transparent  globules 
immersed  in  a  transparent  fluid :  and  that  these  globules  are  larger 
in  the  brain  than  in  the  spinal  marrow.  Prochaska  describes  the 
same  globular  structure,  which  he  represents  as  united  by  a  trans- 
parent elastic  cellular  membrane  disposed  in  fibres.  Monro.f 
in  his  first  inquiries,  thought  that  these  fibres  w'ere  convoluted, 
but  afterwards  acknowledged  that  he  had  been  misled  by  an 
optical  fallacy,  incident  to  the  employment  of  high  magnifying 
powers.  The  WenzelsJ  also  recognized  the  globular  composi- 
tion of  the  nervous  substance,  and  considered  the  globules  them- 
selves to  be  vesicles  filled  with  a  material  either  of  a  medullary 
or  cineritious  appearance,  according  to  the  portion  examined. 
Bauer§  states  that  the  globules  are  of  about  the  same  diameter 
as  the  central  particles  of  the  globules  of  the  blood,  some, 
however,  being  still  smaller ;  and  that  they  are  of  a  gelatinous 
consistence,  and  soluble  in  water.  The  cineritious  substance,  he 
finds,  is  composed  chiefly  of  the  smallest  globuhs,  surrounded 
by  a  large  proportion  of  a  gelatinous  and^  serous  fluid.  The 
medullary  substance,  on  the  other  hand,  is  formed  principally  by 
the  larger  and  more  distinct  globules  which  adhere  together  in 

*  In  his  Anatomical  and  Physical  Commentaries. 

t  On  the  Nervous  System.  f  De  Structura  Cerebri. 

§  Philosophical  Transactions  for  1818,  and  1821. 


ORGANIZATION    OP    THE    NERVOUS    SYSTEM.  257 

lines,  and  have  a  smaller  proportwn  of  fluid,  that  fluid  being  more 
viscid  than  in  the  r.ineritious  substance.  Dr.  Edwards*  has  con- 
firmed by  his  observations,  these  results,  as  far  as  the  general 
globular  composition  of  nervous  matter  is  concerned.  He 
asserts  the  diameter  of  the  globules  to  be  one  three-hundredth 
of  a  millimetre,  which  is  equivalent  to  the  seven  thousand  six 
hundred  part  of  an  inch ;  and  that  these  globules  are  arranged 
in  hncar  series,  constituting  the  primary  linear  fibres.  Beclard 
states  that  he  has  verified  these  observations.! 


2.   The  Nerves, 

586.  The  nerves  are  white  cords  extending  from  different  parts 
of  the  brain  and  spinal  cord,  to  different  parts  of  the  body,  and 
more  especially  to  the  muscles,  the  integuments,  and  other  organs 
of  sense,  and  to  the  viscera  and  blood-vessels.  Their  general 
form  is  cylindrical ;  but  they  divide,  in  their  course,  into  a  great 
number  of  branches,  many  of  which  again  reunite,  or  are  joined 
with  the  branches  of  other  nerves,  so  as  to  form  in  many  parts  a 
complicated  nervous  net-work,  or  plexus,  as  it  has  been  termed 
by  anatomists.  The  nerves  are  usually  spoken  of  as  originating 
in  the  brain  or  spinal  cord,  and  as  proceeding  from  thence  to  their 
termination  in  other,  and  generally  distant  parts.  As  the  united 
branches  would  form  a  cord  of  much  larger  diameter  than  the 
trunk  from  which  they  arise,  it  is  evident  that  the  total  quantity 
of  nervous  matter  they  contain  is  augmented  as  they  proceed  in 
their  course.  When  examined  with  the  microscope,  their  surface 
presents  a  number  of  transverse  lines  or  wrinkles,  which  are 
evidently  for  the  purpose  of  admitting  of  flexion  ;  and  thus  accom- 
modating them  to  the  difierent  movements  of  the  parts  witli*which 
they  are  connected. 

587.  The  nerves  appear  to  consist  of  filaments  of  medullary 
substance,  enclosed  in  a  tough  cellular  membrane.  At  their  origin 
from  the  central  organ,  whether  it  be  the  brain  or  the  spinal  cord, 
they  consist  of  detached  fibrils,  sometimes  isolated,  but  in  general 
arranged  so  as  to  constitute  flat  bands.  There  are  two  such  bands, 
namely,  an  anterior  and  a  posterior  fasciculus,  which  unite  to 
form  each  of  the  nerves  arising  from  the  spinal  cord.  Some 
nerves  are  composed  of  pure  medullary  matter,  as  the  optic  nerve  ; 
but  in  the  greater  number  this  matter  is  so  enveloped  in  a  tough 
cellular  membrane,  which  has  been  termed  by  anatomists  the 
neurilema,  that  it  cannot  distinctly  be  perceived.  In  the  olfactory 
nerves  there  is  an  evident  junction  of  cortical  wdth  medullary 
matter,  but  in  most  others  we  find  nothins;  but  filaments  of  medul- 
lary  matter,  each  of  which  is  contained  in  a  separate  envelope 
or  neurilema,  that  forms  tubes  for  their  reception. 

*  Surla  Structure  Elementaire.  j  See  his  Anatomie  Generals. 

22* 


258  SENSORIAL    FUNCTIONS. 

588.  Many  anatomists  have  attempted  the  investigation  of  the 
minute  structure  of  nervous  fibrils  by  means  of  the  microscope. 
De  la  Torre*  perceived  in  them  globules  similar  to  those  of  which 
the  matter  of  the  brain  is  composed.  Monrof  and  Fontana  des- 
cribe the  nervous  filaments  as  being  connected  by  cellular  sub- 
stance, much  in  the  same  way  as  the  muscular  fibres,  and  arranged 
like  them  in  fasciculi  of  various  sizes.  They  represent  the  ultimate 
fibril- as  being  twelve  times  greater  than  the  muscular  fibre,  hav- 
ilig  a  serpentine  or  tortuous  form,  and  being  composed  of  a  cylin- 
drical canal,  containing  a  viscid  pulpy  matter,  evidently  different 
from  the  substance  of  the  canal  itself.  Reil  has  pursued  this 
investigation  with  still  greater  care  and  minuteness,  and  states  that 
the  ultimate  filaments  differ  in  thickness  from  that  of  a  hair  to  the 
finest  fibre  of  silk.  Their  arrangement  into  larger  and  larger  fas- 
ciculi is  analogous  to  what  we  observe  in  the  structure  of  muscles, 
but  with  this  diflference,  tliat  the  nervous  fibres  in  their  course 
along  the  nerve,  frequently  divide  and  subdivide,  and  are  again 
variously  united  and  conjoined,  so  as  to  produce  an  extensive 
connexion  among  all  the  parts  of  the  same  nerve.  The  mem- 
branous neurilema,  besides  giving  support  to  each  individual  fila- 
ment of  nerve,  and  uniting  them  into  fasciculi,  furnishes  also  a 
general  covering  to  the  whole  nerve  J 

589.  What  has  now  been  stated  must  be  understood  as  appli- 
cable to  nerves  in  general.  Many  differences  have  been  pointed 
out  in  the  structure  of  different  nerves;  but  it  is  not  necessary  to 
descend  into  these  minute  particulars  in  the  general  view  we  are 
now  giving. 

3.  Ganglia. 

590.  Ganglia  are  small  rounded  nodules,  which  are  placed  in 
different  situations  in  the  course  of  nerves,  sometimes  in  the 
trunk  of  a  single  nerve,  and  sometimes  where  two  nerves  unite. 
They  are  most  numerous  on  those  nerves  which  are  distributed 
to  the  viscera,  and  to  the  muscles  of  involuntary  motion.  Their 
appearance  is  very  different  from  that  of  a  mere  dilatation  of  a 
nerve,  being  of  a  reddish-brown  colour,  having  a  minute  fibrous 
texture,  a  firmer  consistence,  and  a  greater  number  of  blood- 
vessels than  ordinary  nerves.     The  nerves  which  pass  out  from 

*  Philosophical  Transactions  for  1769.  |  On  the  Nervous  System. 

:|:  [Ehrenberg  and  some  other  recent  writers  are  of  the  old  opinion,  from 
their  microscopic  researches,  that  the  nerves  are  tubular.  See  Dunglison's 
Physiolog-y,  .3d  edit.  i.  86  ;  and  Miiller's  Physiology,  translated  by  Baly, 
part  3,  Lond.  1838. 

For  an  excellent  epitome  of  the  recent  researches  of  Ehrenberg,  Berres, 
Remak,  Valentin,  Emmert,  Burdach  and  others — into  the  intimate  structure 
and  distribution  of  the  nerves— see  the  British  and  Foreign  Medical  Review, 
No.  XII.  for  Oct.  1838,  p.  394,  and  No.  XIV.  for  April,  1839,  p.  394.] 


THE  EXTERNAL  SENSES TOUCH.  259 

a  ganglion  are  generally  of  a  larger  size  than  those  which  entered 
into  it,  as  if  they  had  received,  in  their  passage  through  it,  an 
additional  quantity  of  matter.  It  would  appear,  from  numerous 
observations,  that  the  filaments  of  the  different  nerves  which  join 
the  ganglion  proceed  through  it  individually  without  interruption, 
but  are,  at  the  same  time,  involved  and  twisted  together  in  a  very 
complicated  manner ;  the  result  being,  that  filatnents  from  many 
different  nerves  are  united  in  the  formation  of  a  new  nerve ;  so 
that  the  parts  to  which  the  nerve  is  distributed  receive  a  supply 
of  filaments  from  many  different  sources,  and  are  in  very  exten- 
sive communication  with  various  parts  of  the  brain,  spinal  cord, 
and  indeed  the  whole  nervous  system. 

591.  Besides  this  junction  and  intertexture  of  nervous  fila 
ments,  the  ganglia  contain  a  soft  semi-fluid  matter,  which  appears 
to  be  analogous  to  the  proper  substance  of  the  brain,  and  like 
the  latter,  may  be  distinguished  into  cineritious  and  medullary 
portions.  It  would  appear,  therefore,  that  the  ganglia  have  some 
peculiar  office  with  regard  to  the  nerves  which  traverse  them, 
and  that  they  do  not  serve  the  purpose  only  of  a  plexus  of  fila- 
ments, establishing  mere  mechanical  connexions  between  them, 
as  some  anatomists  have  alleged. 


CHAPTER    XV. 

THE  EXTERNAL  SENSES. 

592.  The  external  senses  have  usually  been  reckoned  five  in 
number,  namely,  touch,  taste,  smell,  hearing,  and  sight;  but  this 
arrangement  has  reference  more  to  the  organs  by  w^hich  they 
are  exercised  than  to  the  nature  of  the  sensations  they  excite  in 
the  mind.  A  variety  of  sensations  have  been  referred  to  the 
sense  of  touch,  which  are  wholly  different  in  their  kind,  and 
which  are  received  by  means  of  impressions  made  on  the  skin, 
and  also  others  which  are  conveyed  by  nerves  in  other  parts  of 
the  body,  without  any  connexion  with  the  skin.  These  we  shall 
notice  after  we  have  considered  the  sensations  more  peculiarly 
belonging  to  the  sense  of  touch. 

Sect.  I. — Touch, 
1.  Sensation  of  Pressure. 

593.  Every  part  of  the  surface  of  the  body  is  exposed  to  the 
contact  of  foreign  bodies ;  and  in  most  parts  of  the  skin  very 


260  SENSORIAL    FUNCTIONS. 

slight  pressure  made  by  those  bodies  gives  occasion  to  the  primary 
sensation  of  touch,  which  is  in  fact  simply  that  of  resistance  to 
the  part  of  the  skin  on  which  it  presses.  This  sensation  is  quite 
specific,  and  distinguishable  from  all  other  sensations.  It  may 
be  conveyed,  though  less  perfectly,  by  several  of  the  internal 
surfaces  of  the  body,  as  those  of  the  mouth  and  pharynx.  Cer- 
tain parts  of  the  skin  possess,  however,  a  more  peculiar  delicacy 
of  nervous  sensibility  to  the  impressions  of  touch,  and  are  there- 
fore to  be  considered  as  more  especially  the  oi'gans  of  this  sense. 
In  man  the  points  of  the  fingers  are  particularly  employed  for 
receiving  the  finer  impressions  of  touch,  and  for  distinguishing 
the  qualities  of  external  objects,  of  which  this  sense  is  fitted  to 
convey  us  information.  The  greater  vascularity  of  the  skin  of 
the  fingers,  and  greater  development  of  its  papillary  structure, 
have  been  assigned  as  the  causes  of  the  apparent  increase  of  sen- 
sibility with  which  they  have  been  endowed.  There  is  no  doubt, 
however,  that  much  depends  on  the  education  given  to  the  ends 
of  the  fingers,  by  their  constant  employment  in  this  office ;  for 
we  find  that  the  toes  and  other  parts  of  the  body  may,  by  use, 
be  trained  to  the  acquisition  of  an  equal  degree  of  sensibility ;  of 
this  we  see  examples  in  individuals  who  have  been  born  without 
hands.  Parts  where  the  epidermis  is  very  thin,  such  as  the  lips, 
are  also  endowed  with  considerable  sensibility  to  the  impressions 
of  touch,  and  with  the  power  of  discriminating  differences  in 
those  impressions  which  cannot  be  felt  or  appreciated  by  means 
of  the  fingers. 

594.  Professor  Weber  of  Leipsig*  has  made  a  series  of  very 
interesting  experiments  on  the  relative  sensibilities  of  the  skin  in 
different  parts  of  the  body,  with  reference  more  particularly  to 
its  power  of  conveying  to  the  mind  accurate  perceptions  of  me- 
chanical impressions  made  upon  it.  He  found  this  power  pos- 
sessed in  the  highest  degree  by  the  tip  of  the  tongue  and  ends  of 
the  fingers,  the  sensibility  of  which  he  estimated  at  eighty  times 
greater  than  that  of  the  skin  of  other  parts  of  the  body.  He  ob- 
served, also,  that  even  the  skin  in  different  parts  of  the  face, 
when  touched  with  the  points  of  a  pair  of  compasses  opened  to 
a  small  distance,  showed  the  greatest  diversity  in  the  power  of 
conveying  distinct  perceptions  of  touch#as  to  the  object  in  con- 
tact being  single  or  double,  and  as  to  the  distance  between  the 
points,  when  they  were  perceived  to  be  double.: 

2.  Sensations  of  Temperature. 

595.  The  same  organs  which,  when  pressed  by  an  external 
body,  convey  the  impression  of  resistance,  communicate  also 

*  An  account  of  these  researches  is  contained  in  the  Edinburgh  Medical 
Journal,  xl.  p.  83. 


SENSATION    OF    PAIN.  261 

sensations  of  heat  and  cold,  and  nearly  in  the  same  relative  pro- 
portion. Thus,  the  fingers  are  more  sensible  to  variations  of 
temperature  in  the  bodies  they  touch  than  other  parts  of  the  skin 
less  accustomed  to  discriminate  them.  The  lips  are  still  more 
sensible  than  the  fingers  to  the  diflbrences  of  temperature  in  the 
bodies  to  which  they  arc  applied.  This  peculiar  sensibility  aflbrds 
a  ready  mode  of  distinguishing  genuine  diamonds  and  other 
precious  stones  from  such  as  are  counterfeit ;  for  the  former, 
being  better  conductors  of  heat,  produce  a  more  lasting  impression 
of  coldness  when  applied  to  the  lips  or  to  the  tongue. 

The  sensations  of  heat  and  cold  are,  however,  far  from  being 
in  exact  proportion  either  to  the  actual  temperatures  of  the  bodies 
which  are  in  contact  with  the  skin,  or  even  to  the  differences 
between  their  temperature  and  that  of  the  skin.  The  actual 
condition  of  the  sensibility  of  the  skin  at  the  time,  which  depends 
on  a  multitude  of  causes  hereafter  to  be  noticed,  has  a  very  con- 
siderable influence  on  the  sensations.  The  difference  which  is 
observable  in  the  sensibilities  of  the  same  part  to  the  impression 
of  resistance,  and  to  that  of  heat  or  cold,  suggests  a  doubt  whether 
a  different  set  of  nerves  may  not  be  employed  to  transmit  to  the 
brain  these  different  kinds  of  impressions.  We  find  in  certain 
states  of  disease,  that  the  general  sensibility  of  the  surface  of  the 
body  may  be  much  impaired,  and  yet  it  may  preserve  its  sen- 
sitiveness with  regard  to  heat  and  cold;  and  it  is  also  certain, 
that  differences  of  temperature  produce  sensations  in  parts,  the 
stomach  for  instance,  which  are  wholly  disqualified  from  com- 
municating the  feeling  of  resistance. 

3.  Anomalous  Sensations. 

596.  Hunger  and  thirst  are  sensations  referred  to  the  mouth, 
throat,  and  stomach,  which  are  also  quite  specific  in  their  nature, 
though  generally  referred  to  the  sense  of  touch. 

597.  The  same  observation  applies  to  a  variety  of  peculiar 
sensations,  many  of  which  are  common  to  the  whole  surface  of 
the  body,  and  may  even  be  felt  in  some  internal  parts,  but  which 
it  would  be  difficult  to  class,  or  even  completely  enumerate.  The 
sense  of  tingling  and  of  itching  are  examples  of  this  species  of 
sensations.  The  feeling  of  nausea  is  an  undefinable  sensation 
referred  to  the  stomach. 

4.  Sensation  of  Pain. 

598.  Every  sensation  thus  referred  to  the  sense  of  touch,  when 
it  rises  beyond  a  certain  degree,  is  accompanied  with  the  addi- 
tional feeling  of  pain,  which,  if  considerable,  engrosses  the  whole 
attention,  and  eftaces  all  marks  of  discrimination  as  to  its  origin. 


262  SENSORIAL    FUNCTIONS. 

Pain  is  generally  readily  referred  to  a  particular  part  of  the  body, 
as  being  the  origin,  or  as  it  is  commonly  called,  the  seat  of  pain, 
especially  when  the  part  is  external.  But  in  internal  parts,  this 
specific  reference  is  often  extremely  vague  and  imperfect ;  and 
there  frequently  exists  a  general  feeling  of  uneasiness,  often  more 
intolerable  than  any  other,  and  to  which  it  is  impossible  to  assign 
any  particular  locality.  It  may  also  be  observed,  that  in  general 
the  actual  sensibihty  bears  no  relation  to  the  capacity  for  feeling 
pain. 

599.  A  vast  number  of  experiments  were  made  by  Haller, 
with  a  view  to  ascertain  the  comparative  sensibilities  of  the  dif- 
ferent textures  and  organs  of  the  body.  In  general,  those  which 
have  but  a  small  degree  of  vascularity,  such  as  the  cartilages, 
tendons,  hgaments,  fibrous  membranes,  and  bones,  and  even  the 
simple  cellular  texture,  and  serous  membranes,  in  a  state  of 
health,  have  a  very  obscure  degree  of  sensibihty,  when  cut 
across,  pricked  with  a  pointed  instrument,  or  burned  by  a  hot 
iron.  Yet  many  of  these  textures,  though  deficient  in  sensibihty 
to  these  stimuli,  are  yet  extremely  sensible  to  injuries  of  another 
kind,  namely,  forcible  stretching,  when  applied  suddenly  and  in  a 
'degree  which  endangers  the  integrity  of  their  structure.  This  is 
sufficiently  illustrated  by  the  acute  pain  that  is  attendant  on  a 
sprain.  Bones,  also,  though  scarcely  communicating  any  feeling 
of  pain  when  sawn  through  in  the  living  body,  yet  feel  acutely 
the  concussion  produced  by  violent  blows,  as  any  one  may  be  con- 
vinced of  who  has  suffered  a  blow  on  the  knee.  It  is  also  re- 
markable  that  all  those  parts,  which  are  apparently  so  incapable 
of  sensation  under  ordinary  circumstances,  become  highly  sensi- 
ble when  in  a  state  of  inflammation. 

600.  The  internal  parts  of  most  of  the  glands  and  other  solid 
organs,  have  but  little  sensibility ;  and  the  chief  source  of  pain, 
when  they  are  attacked  with  inflammation,  arises  from  the  affec- 
tion spreading  to  the  membranes  which  invest  them.  Inflam- 
mation of  the  mucous  membranes  does  not  occasion  any  propor- 
tionate degree  of  pain.  Those  parts  of  the  body  which  receive 
no  blood-vessels^  as  the  cuticle  and  its  appendages,  the  nails  and 
the  hair,  are  absolutely  insensible.  The  cuticle  consequently  is 
well  adapted  to  protect  the  highly  sensitive  organ  which  it  covers, 
and  to  blunt  its  sensibility. 

601.  Pain  often  arises  from  internal  causes;  from  pressure,  or 
distension,  or  other  mechanical  or  chemical  irritation  applied  to 
nerves ;  or  from  some  changes  taking  place  in  the  texture  of  the 
nerve  itself.  It  will  appear  evident,  on  a  general  review  of  the 
sensibihty  allotted  to  the  different  organs  of  the  body,  that  each 
has  received  from  nature  that  particular  kind  and  degree  which 
is  most  needed,  and  which  best  accords  with  the  relative  import- 


TASTE.  263 

ance  of  its  functions,  and  the  dangers  to  whicii,  in  the  ordinary 
course  of  events,  it  is  exposed. 

5.  The  Muscular  Sense. 

602.  A  very  important  class  of  sensations  has  been  referred 
to  the  sense  of  touch,  which  require  to  be  particularly  distin- 
guished from  the  rest ;  they  are  those  attending  the  contractions 
of  the  voluntary  muscles,  which  render  us  sensible  of  the  move- 
ments of  our  limbs,  and  of  other  parts  which  are  voluntarily 
moved.  These  are  the  feelings  which  give  rise  to  the  idea  of 
extension,  and  which,  combined  with  the  feeling  of  resistance, 
communicate  to  us  a  knowledge  of  the  forms,  magnitudes,  and 
relative  positions  of  external  objects.  Thus,  by  moving  the  hand 
over  the  surfaces  of  bodies,  we  gain  the  ideas  of  their  tangible 
extension,  together  with  most  of  their  mechanical  properties,  such 
as  their  roughness,  hardness,  weight,  texture,  and  dimensions. 
In  these  examinations  we  avail  ourselves  of  the  admirable  pro- 
perties of  the  hand,  an  instrument  which,  by  the  number  and 
variety  of  its  parts,  and  the  motions  of  which  they  are  capable, 
is  exquisitely  fitted  for  procuring  us  this  useful  kind  of  knowledge. 
By  the  perceptions  we  acquire  in  infancy  from  the  active  employ- 
ment of  the  limbs  in  various  kinds  of  progressive  motion,  our 
sphere  of  knowledge  of  the  material  world  is  prodigiously  ex- 
tended ;  and  these  perceptions  are  an  important  source  of  gra- 
tification, in  consequence  of  the  feelings  of  pleasure  with  which, 
by  the  beneficent  ordination  of  nature,  the  active  exercise  of  the 
voluntary  muscles  is  accompanied. 

603.  The  sense  of  touch,  in  the  comprehensive  view  which 
we  have  now  taken  of  it,  is  unquestionably  the  most  important 
of  all  our  external  senses,  bringing  us  more  immediately  ac- 
quainted with  the  essential  qualities  of  the  material  world,  and 
laying  the  great  foundations  of  all  the  knowledge  which  the  other 
senses  supply,  by  a  reference  to  the  ideas  derived  from  touch. 


Sect.  II. —  Taste. 

604.  It  was  the  fashion  among  the  French  -metaphysicians  to 
resolve  all  the  senses  into  that  of  touch;  so  that  in  speaking  of 
vision,  for  instance,  they  would  allege  that  we  see  by  means  of 
the  light  which  touches  the  retina.  But  this  is  a  mere  refine- 
ment not  warranted  by  facts,  and  in  which  the  real  distinctions 
existing  among  the  sensations  themselves  are  overlooked, 

605.  If  any  of  the  senses  could  be  considered  as  a  finer  sense 
of  touch,  it  would  be  that  of  taste,  by  which  we  receive  impres- 
sions of  a  peculiar  kind  from  the  sapid  qualities  of  bodies  in 


264  SENSORIAL    FUNCTIONS. 

contact  with  the  upper  surface  of  the  tongue.  This  sense  is 
manifestly  intended  to  guide  us  in  the  choice  of  our  food,  and  it 
is  accordingly  placed  at  the  entrance  of  the  alimentary  canal. 

1.  Organs  of  Taste. 

606.  The  principal  organ  of  taste  is  the  tongue,  bu^several  of 
the  neighbouring  organs  are  auxiliaries  in  the  exercise  of  this 
sense.  The  soft  parts  of  the  mouth  consist  of  the  lips  and  cheeks, 
the  gums,  the  soft  palate,  the  velum,  uvula,  tongue,  the  membra- 
nous hning  of  the  mouth',  and  the  salivary  glands.  The  osseous 
parts  are  the  upper  and  lower  maxillary  bon'es,  the  teeth,  and  the 
palate  bones. 

607.  The  lips  and  cheeks  are  principally  composed  of  muscles; 
they  are  covered  on  the  outside  by  the  common  integuments, 
and  lined  within  by  the  membrane  of  the  mouth,  in  which  are 
situate  numerous  mucous  glands.  The  membrane  of  the  mouth 
is  covered  with  fine  villi,  which  are  most  conspicuous  on  the 
edges  of  the  lips.  A  small  doubling  of  this  membrane  is  met 
with  in  the  middle  of  both  the  upper  and  under  lips,  which  fixes 
them  more  closely  to  the  jaws.  These  doublings  have  been 
termed  ihefrcBua  lahiorum.  The  union  of  the  lips  at  the  corners 
of  the  mouth  form  what  has  been  called  the  commissures  of  the 
lips. 

608.  The  gums,  which  surround,  and  firmly  adhere  to  the  col- 
lar of  the  teeth,  are  very  vascular,  and  composed  of  a  dense  and 
compact  cellular  substance. 

609.  Thepa/afeis  divided  into  the  palatum  durum,  and  palatum 
molle.  The  former  is  composed  of  the  palate  plates  of  the  upper 
jaw,  covered  by  periosteum,  and  by  the  membrane  of  the  mouth, 
which  here  forms  numerous  rugse.  The  soft  palate,  or  velum 
pendulum  palati  is  the  name  of  that  membranous  curtain  which 
hangs  from  the  posterior  edge  of  the  ossa  palati,  and  pterygoid 
processes,  and  forms  a  flexible  partition  between  the  mouth ' 
and  throat.  It  serves  to  conduct  the  fluids  of  the  nose  down- 
wards, and  at  the  same  time  acts  as  a  valve  in  preventing  the 
passage  into  the  nostrils  of  what  is  swallowed.  In  the  middle 
of  the  edge  of  the  velum,  a  conical  papilla,  termed  the  uvula,  is 
met  with,  and  in  the  relaxed  state  hangs  pendulous  over  the  root 
of  the  tongue. 

610.  The  tongue  is  a  complex  organ,  principally  consisting  of 
a  mass  of  muscular  fibres,  irregularly  disposed,  and  crossing  each 
other  in  a  great  variety  of  directions,  and  being  also  intermixed 
with  a  soft  kind  of  fat.  It  is  invested  by  a  mucous  membrane, 
being  a  continuation  of  that  which  fines  the  mouth  generally,  and 
which  here  presents  large  and  numerous  papillcB.  These  papillae 
are  distinguished  by  anatomists  into  three  kinds,  according  to 


ORGANS    OF    TASTE.  205 

their  size,  form,  and  situation.  Tiic  first  class  of  these,  called 
papillce,  maximce,  lentlculares,  or  capitatce,  are  by  much  the 
largest,  have  a  lenticular  form,  with  round  heads  and  short  stems. 
They  are  placed  at  the  base  of  the  tongue,  in  superficial  fossulee. 
They  have  been  regarded  as  auxiliary  salivary  glands,  and  have 
each  a  perforation  in  the  middle  of  their  convex  surface,  for  the 
excretion  of  mucus.  The  second  class,  or  papillcB  medicB,  or 
semi-hrdiculares,  are  much  smaller  than  the  former,  and  are 
scattered  over  the  upper  surface  of  the  tongue,  at  some  distance 
from  each  other ;  their  form  is  cylindric,  while  some  are  termi- 
nated by  a  round,  but  not  dilated  extremity.  Others  are  more 
or  less  tuberculated  at  the  summit.  The  third  class,  or  papillce 
minima;,  which  have  also  been  termed  conicce,  or  villosce,  are  ex- 
ceedingly numerous,  but  of  very  minute  size.  They  cover  almost 
the  whole  of  the  upper  surface  of  the  tongue,  but  are  most 
abundant  towards  the  tip,  where  the  sense  of  taste  is  most  acute. 

611.  The  membrane  covering  the  root  of  the  tongue  abounds 
with  mucous  follicles.  At  the  root  of  the  tongue,  and  behind  the 
papilla  maximee,  there  is  a  hole  or  deep  depression,  called  the 
foramen  cacum  Morgagni,  which  penetrates  only  a  small  way 

into  the  substance  of  the  tongue,  and  receives  the  mouths  of  se- 
veral excretory  ducts  that  open  into  it.  A  line  is  also  observable 
runninar  forwards  alons;  the  middle  of  the  tongue,  from  the  fora- 
men  ccecum  ;  this  is  the  linea  Ungues  mediana.  The  tongue  is 
somewhat  restrained  in  its  motions  by  the  franum  lingiics,  which 
is  formed  by  a  duplicature  of  membrane  at  its  under  part,  con- 
necting it  with  the  jaw. 

612.  All  sapid  substances  require,  in  order  to  produce  an  im- 
pression of  taste,  to  be  applied  in  a  state  of  solution  to  the  nerves 
of  that  sense.  Nature  has  accordingly  provided  a  fluid  secretion 
for  the  purpose  of  efl'ecting  their  solution,  and  difllising  them  over 
a  sufficient  extent  of  the  surface  of  the  tongue.  This  secretion, 
which  is  the  saliva,  is  prepared  by  the  salivary  glands,  which 
consist  of  three  large  glands  on  each  side  of  the  face,  namely, 
the  parotid,  the  submaxillary,  and  the  sublingual.  The  parotid  is 
the  largest  of  the  three,  and  occupies  the  whole  space  between 
the  ear  and  the  angle  of  the  lower  jaw  ;  its  excretory  duct,  called 
Steno's  salivary  duct,  passes  off  from  the  upper  and  fore  part  of 
the  gland,  and  perforates  the  buccinator  muscle,  so  as  to  open  in 
the  inside  of  the  cheeks,  opposite  to  the  second  or  third  molar 
tooth  of  the  upper  jaw.  The  submaxillary,  or  inferior  maxillary 
gland,  is  situate  on  the  inside  of  the  angle  of  the  lower  jaw;  its 
duct  is  called  the  ductus  Whartonii,  and  it  terminates  by  a  small 
orifice  on  the  surface  of  a  papilla  on  the  side  of  the  frsenum 
linguae.  The  sublingual  gland  is  still  smaller,  and  is  under  the 
anterior  portion  of  the  tongue  above  the  duct  of  Wharton,  and 

23 


366 


SENSORIAL    FUNCTIONS. 


its  ducts  open  by  several  orifices  arranged  in  a  line  near  the 
gums,  a  little  to  the  outside  of  the  fr^nuni. 

2.  Ftmciions  of  Taste. 

613.  Attempts  have  often  been  made,  but  with  no  great  suc- 
cess, to  establish  a  classification  of  tastes.  The  general  characters 
of  the  tastes  denominated  acid,  sweet,  bitter,  saline,  alkaline, 
aromatic,  astringent,  acrid,  and  spirituous,  are  sufficiently  known, 
but  their  combinations  are  endless;  and  there  exists  besides  these, 
a  greater  number  of  other  tastes,  which  it  would  be  impossible 
to  reduce  to  any  of  the  above  classes. 

614.  The  principle  on  which  sapid  bodies  act  upon  the  tongue 
is  probably  resolvable  in  all  cases  into  chemical  action.  It  is 
observed,  accordingly,  that  substances  which  are  in  a  sohd  form 
and  absolutely  insoluble  in  saliva,  are  invariably  tasteless ;  just 
as  in  chemistry  it  is  an  established  axiom  that  bodies  do  not  act 
chemically  unless  they  are  either  in  a  liquid  or  gaseous  state. 
Mr.  Mayo  observes,  that  the  sensations  of  taste  are  not  perfect 
until  the  mouth  is  closed,  and  the  tongue  pressed  against  the 
palate,  by  which  means  the  sapid  liquid  is  brought  into  more 
exact  contact  with  the  surface  of  the  tongue,  and  perhaps  forced 
into  the  texture  of  its  mucous  membrane. 

615.  The  organ  of  taste  appears  to  be  exclusively  the  upper 
and  papillated  surfaceof  the  tongue  ;  for  although  the  impressions 
of  this  sense  are  often  referred  to  the  palate,  inside  of  the  cheeks 
and  gums,  accurate  discrimination  shows  that  this  reference  to 
the  parts  against  which  the  sapid  body  is  pressed  by  the  tongue, 
is  deceptive,  that  the  real  seat  of  the  sense  is  confined  to  the 
tongue  itself,  and  that  its  immediate  organs  are  the  papillae,  and 
more  particularly  those  denominated  conicce  or  mllosce.  which 
are  highly  vascular  and  erectile,  being  observed  to  rise  above 
the  surface  of  the  tongue  when  any  sapid  substance  is  applied  to 
it.     On  the  other  hand,  no  papillae  are  discoverable  on  the  palate. 

Some  substances,  such  as  peppermint,  produce  a  pungent 
impression  on  the  back  of  the  fauces;  and  others,  again,  such  as 
mezereon,  excite  in  the  same  part  a  peculiar  sense  of  irritation, 
which  appears  to  proceed  more  from  a  generally  acrimonious 
property,  afi^ecting  particularly  the  nervous  surfaces,  than  from 
any  real  sapidity;  indeed,  if  the  impressions  made  on  the  organs 
of  smell  be  excluded  from  consideration,  it  will  be  found  that  the 
extent  of  the  part  of  the  tongue  which  really  receives  impressions 
of  taste,  is  very  limited.  Mr.  Mayo*  states  that  salt,  aloes,  sugar, 
or  acids,  which  excite  the  most  acute  sensation  when  applied  to 
the  tip  or  edge  of  the  tongue,  produce  none  at  the  fore  or  upper 

*■  Outlines  of  Human  Physiology. 


ORGANS    OF    SMELL.  267 

part  of  the  organ,  or  on  the  hard  palate.  But  at  the  back  of  the 
tongue  they  again  excite  sensation  enough  to  be  distinguishable, 
and  they  are  still  more  perfectly  tasted  on  the  middle  of  the  soft 
palate  and  uvula.  The  participation  of  the  soft  palate  in  the 
sense  of  taste  has  been  recently  pointed  out  by  MM.  Guyot  and 
Admyrauld,  and  has  been  carefully  verified  by  Mr.  Wheatstone 
and  Mr.  Mayo.  These  latter  gentlemen  did  not  find  that  one  taste 
was  perceived  more  distinctly  than  another,  at  any  point  of  the 
tongue  or  soft  palate. 

There  is  no  circumstance  more  remarkable,  with  relation  to 
this  sense,  than  its  intimate  connexion  with  that  of  smeil  of  which 
we  are  next  to  speak.* 


Sect.  III. — Smell. 

616.  The  purpose  answered  by  the  sense  of  smell  is  apparently 
to  guard  against  the  introduction  into  the  lungs  of  injurious  efflu- 
via, as  that  of  taste  is  to  watch  over  the  qualities  of  the  substances 
introduced  into  the  stomach.  Its  seat  is  the  Schneiderian  mem- 
brane lining  the  cavity  of  the  nostrils;  and  more  particularly  the 
turbinated  bones,  which  are  placed  so  as  to  catch  the  odorous 
effluvia  directly  as  these  enter  the  nostrils,  and  which,  together 
with  the  cavities  or  sinuses  in  the  contiguous  bones,  contribute  to 
extend  considerably  the  surface  on  which  the  impression  of  these 
effluvia  is  made. 


1.  Organs  of  Smell. 

617.  The  organ  of  smell  may  be  divided  into  the  external  and 
internal  farts. 

The  external  part,  oi*  nose,  properly  so  called,  consists  princi- 
pally of  an  upper  bony  portion  commonly  called  \]\e  bridge  of  the 
nose,  composed  of  the  ossa  nasi,  supported  by  a  vertical  process 
from  the  ethmoid  bone,  together  with  the  vomer,  and  an  inferior 
cartilaginous  portion,  of  which  the  middle  prominence  is  called 

*  [Much  dissidence  has  existed  as  to  the  precise  nerve  of  taste.  The  view 
generally  embraced  is  that  of  Sir  Charles  Bell  ;  who  considers  the  ninth  pair, 
which  arises  from  the  anterior  or  motor  tract  of  the  spinal  marrow,  as  the 
nerve  of  motion  for  the  tongue  ;  the  Ungual  branch  of  the  fifth,  a  nerve  having 
a  posterior  root,  as  the  nerve  of  taste,  and  the  glonso-pharyngeal,  as  the  nerve 
by  which  the  tongue  is  associated  with  the  pharynx  in  the  function  of  deglu- 
tition. Recent  researches,  by  Messrs.  Panizza  and  Broughton,  encourage 
the  idea  that  the  hypoglossal,  or  ninth  pair,  is  the  nerve  of  motion  for  the 
tongue  ;  the  lingual  branch,  or  the  fifth  pair,  the  nerve  of  general  sensibility, 
and  the  glosso-pkarjpigeal,  the  nerve  of  gustation.  The  matter  is  undecided, 
but  the  weight  of  evidence  appears  to  be  in  favour  of  the  first  opinion.  Dun» 
glison's  Physiology,  3d  edit.  i.  112.] 


268  SENSORIAL    FUNCTIONS. 

the  dorsum;  the  rounded  portions  below  are  the  alee  nasi,  or  wings ; 
and  the  cartilage  forming  the  partition  between  the  nostrils  is 
termed  the  columna  nasi.  These  cartilages  have  a  degree  of 
elasticity  which  preserves  the  form  of  the  organ. 

The  internal  parts  are  contained  in  the  cavities  of  the  nostrils, 
which  are  divided  by  the  septum,  narium  into  two  lateral  passages. 
In  the  upper  part  of  each  nostril,  there  is  a  spongy  bone  of  a 
lengthened  but  irregular  shape,  the  os  turhinatum  superius,  which 
belongs  to  the  ethmoid  bone.  Below  this  extends  the  inferior 
turbinated  bone,  so  that  the  general  cavity  is  divided  by  these 
bones  into  three  passages  for  the  air,  running  from  before  back- 
wards ;  they  have  been  respectively  nained  by  Hall  the  meatus 
narium  superior,  medius,  and  infei^ior. 

618.  The  extent  of  the  cavities  belonging  to  the  nose  is  much 
increased  by  their  communicating  with  various  sinuses,  or  cavities 
in  the  neighbouring  bones,  namely,  the  frontal,  splienoidal,  and 
maxillary  sinuses.  Posteriorly  the  nostrils  open  into  the  pharynx, 
by  two  orifices,  termed  the  posterior  nares.  All  these  cavities, 
together  with  the  sinuses  with  which  they  communicate,  are  lined 
with  a  sensible  and  delicate  mucous  membrane,  termed  \\\e  pitui- 
tary membrane,  or  sometimes,  from  the  anatomist  who  first  accu- 
rately described  it,  the  membrana  Sclmeideriana.  The  lower 
part  of  the  lacrymal  sac  becoming  somewhat  narrower,  but  with- 
out forming  any  valve,  passes  into  the  nose,  under  the  name  of 
lacrymal  duct,  canalis,  nasalis,  or  ductus  ad  nasum.  At  the  pos- 
terior part  of  the  nares  is  the  opening  of  the  Eustachian  tube, 
leading  to  the  tympanic  cavity  of  the  ear. 

2.  Function  of  Smell. 

619.  The  impressions  made  on  the  two  senses  of  taste  and 
smell,  have  not  only  a  great  affinity  to  each  other,  but  also  an 
intimate  connexion;  inasmuch  as  many  of  those  referred  to  the 
organ  of  taste  are  in  reality  made  on  the  organ  of  smell,  and  are 
not  perceived  at  all  if  the  nostrils  be  closed,  and  the  odorous  effluvia 
arising  from  the  substance  placed  on  the  tongue  be  consequently 
prevented  from  ascending,  and  acting  on  the  sentient  membrane 
lining  their  cavity.  When  the  Schneiderian  membrane  is  inflamed, 
the  taste  of  all  those  substances,  of  which  the  flavour  consists  in 
their  scent  alone,  is  altogether  lost ;  and  as  this  is  the  case  with 
by  far  the  greater  number  of  substances  employed  as  food,  the 
sense  of  taste  appears,  under  these  circumstances,  to  be  very 
imperfect.  Both  these  senses,  but  particularly  that  of  smell,  are 
possessed  by  man  in  a  degree  very  inferior  to  that  in  which  they 
exist  in  the  lower  animals. 

620.  It  is  essential  to  the  exercise  of  this  sense,  that  the  mem- 
brane of  the  nostrils  should  be  in  a  moist  state ;  for  when  it  hap- 


HEARING. — ACOUSTIC    PRINCIPLES.  269 

pens  to  be  dry  from  a  deficiency  of  secretion,  the  extrenaifies  of 
the  olfactory  nerves  are  unfitted  for  the  reception  of  the  impres- 
sion of  odours.  It  is  also  necessary  for  smelling  that  the  air 
charged  with  the  odorous  effluvia  should  impinge  with  some 
degree  offeree  against  the  Schncidcrian  membrane. 

The  seat  of  greatest  sensibility  to  odours  is  the  upper  part  of 
the  nostrils ;  and  the  form  of  the  nose  and  of  its  apertures  are 
obviously  adapted  to  direct  the  stream  of  air  towards  those  parts. 
It  is  found,  accordingly,  that  when  the  nose  has  been  destroyed 
by  disease,  the  smell  is  greatly  impaired,  if  not  altogether  lost.* 

621.  Odours  as  well  as  tastes  have  been  attempted  to  be  classed. 
Linnseus  distributed  them  into  seven  classes:  1,  ambrosial,  of 
which  the  smell  of  the  rose  and  musk  are  examples;  2,  fragrant, 
as  the  smell  of  the  lily,  of  the  jasmin,  and  of  saffron  ;  these  are 
more  evanescent  than  the  former;  3d,  arojnatlc,  as  the  smell  of 
the  laurel ;  4,  alliaceous,  partaking  of  the   odour  of  garlic  ;  5, 

fetid,  exemplified  in  valerian  and  mushrooms ;  6,  virous,  or 
narcotic,  as  in  the  smell  of  opium  ;  7,  nauseous,  as  that  of  the 
gourd,  melon,  and  cucumber.  But  this  classification  is  obviously 
incomplete,  as  it  omits  several  very  distinct  classes  of  odours, 
such  as  that  of  alcohol,  of  sdther,  of  camphor,  of  ammonia,  of 
chlorine,  6tc. 

622.  Any  very  acrid  or  stimulating  vapour  admitted  to  the 
nostrils,  instead  of  producing  the  sensation  of  smell,  gives  rise  to 
mere  painful  irritation,  which  excites  sneezing,  and  a  copious 
secretion  of  mucus. 

Sect.  IV. — Hearing. 
1.  Acoustic  Principles. 

623.  The  object  of  the  sense  of  hearing  is  to  convey  to  us  certain 
impressions  made  on  the  nerves  of  the  ear  by  the  vibrations  of  the 
air;  which  vibrations  are  the  result  of  some  mechanical  impulse 
communicated  to  it  by  the  motion  of  a  body  at  a  distance.  Other 
media  besides  air  are  also  capable  of  transmitting  sonorous  vibra- 
tions to  the  organ  of  hearing;  thus  water  is  known  to  convey  sounds 
to  great  distances;  and  solid  bodies  possess  the  same  power  in  a 
degree  proportioned  to  their  molecular  elasticity.  If  the  body 
which  is  the  source  of  sound  be  insulated  from  any  such  medium,  its 
vibrations  cannot  be  communicated,  and  no  sound  is  heard.  Thus 
if  a  bell  be  placed  in  the  receiver  of  an  air-pump,  in  proportion 

*  [The  olfactory  or  first  pair  of  nerves  is  distributed  to  this  part  of  the 
nasal  fossae;  and  the  fifth  pair  to  the  lower  portion  of  the  nasal  fossae. 
The  integrity  of  both  seenris  to  be  necessary  for  olfaction  ;  althoiisrh  the  first 
pair  appears  to  be  the  proper  nerve  of  smell ; — the  fifth  pair  being  the  nerve 
«f  general  sensibility.] 

23* 


270  SENSORIAL    FUNCTIONS. 

as  the  air  is  exhausted  the  sound  it  produces  when  struck  becomes 
more  and  more  faint,  till  at  length,  when  the  rarefaction  has  been 
carried  a  certain  length,  it  is  quite  inaudible.  If  the  same  bell 
be  placed  in  a  vessel  of  condensed  air,  the  sound  it  gives  out  will 
be  louder  than  in  air  of  the  ordinary  density. 

624.  The  velocity  with  which  sound  is  transmitted  in  air  of 
the  same  density  is  uniform  at  all  distances,  and  for  all  sounds 
whatsoever.  As  the  air  of  the  atmosphere  varies  in  its  density, 
and  also  in  its  degrees  of  humidity,  the  velocity  of  sound  is  not 
constantly  the  same.  It  may  be  taken  at  an  average  as  being 
1100  feet  in  a  second,  or  nearly  thirteen  miles  in  a  minute. 

2.  Organ  of  Hearing. 

625.  The  organ  of  hearing  is  divided  into  the  external  and  the 
internal  ear. 

626.  The  external  ear,  comprehends  the  auricula,  or  ear,  pro- 
perly so  called,  and  the  meatus  auditorius  externus. 

627.  The  auricula  is  chiefly  composed  of  an  elastic  cartilage 
bent  into  various  folds  and  hollows,  and  covered  with  a  thin  layer 
of  common  integuments,  the  lower  fold  of  which,  enlarged  by 
the  addition  of  cellular  substance,  forms  the  depending  part  called 
the  lohe  of  the  ear.  The  cartilaginous  portion  is  termed  the 
pinna,  or  ala.  Its  outer  circle,  or  prominent  margin,  is  called, 
from  its  winding  direction,  the  helix.  The  semicircular  ridge 
within  this  is  the  antihelix ;  and  the  small  protuberance,  in  which 
the  helix  appears  to  terminate  below  at  its  inner  edge,  is  called 
the  tragus,  from  its  being  frequently  covered  with  hair.  Another 
eminence,  nearly  opposite  to  this,  below  the  anterior  extremity 
of  the  antihelix,  and  projecting  outwards  over  the  hollow  of  the 
ear,  is  called  the  antitragus.  Between  the  helix  and  antihelix,  is 
the  cavity  called  the  scaphus,  or  fossa  navicularis. 

628.  The  concha  is  a  large  depression  under  the  antihelix,  and 
divided  into  two  parts  by  the  hehx.  The  lower  of  these  leads  to 
the  meatus  auditorius,  a  passage  which  at  its  commencement  is 
composed  of  cartilage,  and  farther  on  is  joined  to  the  orifice  of 
the  same  name  in  the  temporal  bone.  The  cartilaginous  tube  is 
lined  by  a  soft  membrane,  giving  rise  to  hairs,  and  containing 
small  glands,  the  glandulce  ceruminosce,  which  secrete  the  wax  of 
the  ear.  This  cartilaginous  portion  of  the  ear  is  attached  to  the 
temporal  bone  by  several  ligaments  and  muscles  ;  the  effects  of 
which  in  moving  the  different  parts  of  the  external  ear  are  in 
general  very  little  sensible. 

629.  The  membrane  lining  the  meatus  is  continued  along  the 
osseous  portion  of  the  canal,  which  is  closed  by  the  dymm  of  the 
ear,  or  memhrana  tympani.  This  is  a  firm,  oval,  and  almost 
transparent  membrane,  fixed  in  an  osseous  groove  at  the  bottom 


ORGAN    OF    HEARING.  271 

of  the  meatus,  across  -which  it  hes  in  an  oblique  position.  It  is 
shghtly  concave  on  the  external  side ;  and  is  capable  of  being 
stretched  or  relaxed  by  the  action  of  particular  niuscles. 

630.  The  membrane  of  the  tympanum  divides  the  external 
from  the  internal  ear.  Behind  it  we  find  an  irregular  cavity, 
called  the  tyjnpanic  cavity,  or  cavity  of  the  tympanum,  which  is 
filled  with  air  ;  it  is  about  seven  or  eight  lines  wide,  and  about 
half  that  space  in  breadth  ;  and  is  every  where  lined  by  a  fine 
membrane.  It  has  four  openings ;  the  first  is  the  small  orifice 
of  a  passage  of  communication  with  the  back  of  the  cavity 
of  the  nostrils,  which  is  called  the  Eustachian  tube,  and  is 
shaped  like  a  trumpet,  expanding  as  it  approaches  the  fauces. 
The  second  aperture  leads  to  a  number  of  irregular  cells, 
formed  in  4he  mastoid  process  of  the  temporal  bone,  and 
called  the  mastoid  cells.  At  the  back  part  of  the  tympanum  we 
find  an  oval  opening,  called  the  fenestra  ovalis,  and  below  this  a 
round  perforation,  termed  the  fenestra  rotunda.  Between  these 
fenestree,  is  a  bony  eminence,  called  the  promontory. 

631.  Within  the  cavity  of  the  tympanum  are  contained  four 
small  bones,  the  ossicula  auditus,  placed  in  a  series  or  chain  ex- 
tending across  from  the  membrana  tym.pani  to  the  fenestra  ovalis. 
The  malleus,  or  hammer,  is  the  first  of  these  bones  ;  a  long  pointed 
process  from  which  the  handle  is  fixed  to  the  membrana  tympani. 
It  is  articulated  by  its  round  head  with  the  next  bone,  the  incus, 
or  anvil,  which  much  resembles  in  its  shape  a  molar  tooth,  having 
a  body  and  two  unequal  crura.  With  the  longest  of  these  pro- 
cesses is  articulated  the  os  orbicularis,  of  a  rounded  figure,  and 
smaller  than  a  grain  of  mustard  seed.  It  forms  the  medium  of 
connexion  between  the  incus  and  the  stapes,  which  is  the  last 
bone„in  the  series,  and  is  so  named  from  its  striking  resemblance 
in  form  to  a  stirrup.  The  base  of  the  stapes  is  fixed  to  the  margin 
of  the  fenestra  ovalis,  which  it  accurately  closes.  The  articula- 
tions of  these  minute  bones  are  furnished  with  capsular  ligaments, 
and  all  the  apparatus  of  the  larger  joints ;  appropriate  muscles 
being  also  provided  for  their  movements.  Between  the  malleus 
and  the  incus,  there  passes  a  small  nervous  cord  which  crosses 
the  tympanum,  and  is  accordingly  named  the  chorda  tympani. 

632.  The  principal  cavity  of  the  organ  of  hearing  is  situate 
still  more  internally,  and  from  the  intricacy  of  its  winding  sinuo- 
sities it  has  received  the  general  name  of  the  labyrinth.  All  its 
cavities  and  passages  are  lined  with  a  very  delicate  periosteum, 
and  filled  with  a  watery  fluid,  and  within  them  is  suspended  a 
pulpy  membrane  of  a  similar  shape,  on  which  are  distributed 
various  nervous  filaments  presently  to  be  described.  This  saccular- 
shaped  membrane  is  termed  by  Breschet  the  membranous  laby- 
rinth, in  order  to  distinguish  it  from  the  osseous  labyrinth,  in 
which  it  is  contained.    It  forms  one  continuous  closed  sac  extend- 


272  SENSORIAL    FUNCTIONS. 

ing  within  the  vestibule  and  canals,  excepting  those  of  the  cochlea; 
and  contains  a  fluid,  perfectly  similar  to  the  perilymph,  and 
termed  by  Blainville,  vitrine  auditive,  which  intervening  between 
it  and  the  osseous  parietes  of  the  labyrinth,  surrounds  it  on  all 
sides,  and  prevents  its  coming  in  contact  with  those  bones. 

The  central  cavity,  in  which  all  these  passages  meet,  is  termed 
the  vestibule ;  it  is  of  an  oval  figure,  and  is  situate  nearly  in  the 
centre  of  the  os  petrosum,  and  at  the  inner  side  of  the  fenestra 
ovalis.  On  the  side  of  the  vestibule  next  to  the  mastoid  process, 
there  are  five  orifices  leading  to  the  three  semicircular  canals,  as 
they  are  called,  or  passages  formed  within  the  substance  of  the 
bone.  The  extremities  of  two  of  these  canals  unite,  and  termi- 
nate by  a  common  opening  ;  hence  there  appear  in  the  vestibule 
only  five  openings,  instead  of  six.  These  canals  are  distinguished 
by  the  names  of  the  superior,  or  vertical,  the  posterior,  or  oblique, 
and  the  exterior,  or  horizontal.  They  each  form  a  curvature  of 
more  than  three-fourths  of  a  circle,  and  have  an  enlargement, 
termed  ampulla,  or  cavitas  elliptica,  at  one  end,  the  other  ex- 
tremity being  nearly  of  the  same  size  as  the  rest  of  the  canal. 

633.  The  cochlea,  which  is  the  third  division  of  the  labyrinth, 
has  a  conical  shape,  and  is  situate  at  the  anterior  part  of  the  os 
petrosum,  and  at  the  fore-part  of  the  vestibule,  with  its  base  to- 
wards the  meatus  auditorius  internus,  and  its  apex  in  the  opposite 
direction ;  that  is,  facing  outwards.  It  contains  a  double  spiral 
passage,  winding  round  like  the  shell  of  a  snail.  This  passage 
begins  by  a  round  hole  from  the  vestibule,  and  after  forming  two 
turns  and  a  half,  becomes  suddenly  smaller  on  arriving  at  the 
apex,  where  it  communicates  with  a  similar  tube  which  takes  its 
rise  at  the  base  of  the  cochlea  from  the  fenestra  rotunda,  for- 
merly noticed  as  one  of  the  apertures  of  the  cavity  of  the.  tym- 
panum ;  but  which  is  closed  by  a  membrane.  The  partition 
which  divides  these  two  winding  passages  is  called  the  lamina 
spiralis,  or  septum  scalx ;  for  the  passages  themselves  are  known 
by  the  name  of  the  scales  cochlece ;  that  which  communicates  with 
the  vestibule  being  distinguished  as  the  scala  vestibuli,  and  the 
other,  from  its  connexion  with  the  tympanum,  the  scala  tympani. 
The  central  bony  pillar,  around  which  these  turns  are  made,  has 
a  horizontal  direction,  and  is  called  the  modiolus.  It  has  the 
shape  of  a  cone,  at  the  apex  of  which  is  situate  another  hollow 
cone  in  a  reverse  position,  termed  the  infundibulum,  which,  how- 
ever, is  an  imperfect  funnel,  having  a  common  apex  with  the 
modiolus,  and  its  base  being  covered  by  the  apex  of  the  cochlea, 
which  is  called  the  cupola. 

634.  It  has  been  supposed  that  when  the  fluid  in  these  cavities 
is  in  too  great  a  quantity,  the  superfluous  portion  is  carried  off 
by  two  minute  canals  or  aqueducts,  discovered  by  Cotunnius. 
One  of  these  opens  into  the  bottom  of  the  vestibule,  and  the  other 


FUNCTION    OF    HEARING.  273 

into  the  cochlea,  near  the  fenestra  rotunda.  They  bear  the 
names  respectively  of  the  aqucechictus  vestihuU  and  aqiioiductus 
cochlece.  They  both  pass  through  the  os  pelrosum,  and  commu- 
nicate with  the  cavity  of  the  cranium. 

The  form  of  that  part  of  the  membranous  labyrinth  which 
occupies  the  cavity  of  the  vestibule,  and  which  has  accordingly 
received  the  name  of  the  membranous  vestibule,  though  having  a 
general  resemblance  to  that  of  the  cavity  itself,  yet  differs  from 
it  in  some  degree,  being  composed  of  two  sacs  opening  into  each 
other.  One  of  these  sacs  is  termed  the  utricle ;  and  the  other 
the  sacculus.  Each  sac  contai;is  in  its  interior  a  small  mass  of 
white  calcareous  matter  resembling  powdered  chalk,  and  which 
seems  to  be  suspended  in  the  fluid  contents  of  the  sac  by  means 
of  a  number  of  nervous  filaments,  derived  from  the  acoustic 
nerves,  and  of  which  they  appear  to  be  the  ultimate  ramifica- 
tions.* 

635.  Through  an  opening  at  the  base  of  the  modiolus,  a  branch 
of  the  auditory  nerve,  which  has  entered  by  the  meatus  audito- 
rius  intern  us,  passes  into  the  funnel-shaped  cavity,  and  is  thence 
extended  through  the  spiral  canals;  while  another  branch  passes 
backwards  through  the  vestibule,  and  dividing  into  several 
branches,  enters  the  orifices  of  the  semicircular  canals.  The 
minute  branches  perforate  a.  part  of  the  bone,  which  has  been 
termed,  from  its  appearance,  the  cribriform  plate. 

3.  Function  of  Hearing. 

686.  We  thus  see  that  the  ear  is  an  organ  extremely  compli- 
cated in  its  structure,  evidently  intended  to  convey  the  sonorous 
undulations  of  the  air,  after  they  are  collected  by  the  more 
external  parts  of  the  organ,  to  the  branches  of  the  auditory 
nerve,  which  are  spread  over  the  membranes  lining  the  different 
cavities  of  the  labyrinth,  and  the  cretaceous  bodies  suspended 
within  those  membranes.  We  may  therefore  distinguish  the 
several  parts  of  the  apparatus  employed  for  this  purpose,  ac- 
cording as  they  are  merely  designed  to  collect  the  aerial  undula- 
tions, and  increase  their  intensity  by  concentrating  them  into  a 
smaller  space ;  or  according  as  they  contain  the  expanded 
nerves  on  which  the  impression  is  ultimately  made.  It  appears 
that  the  medium   by  which  this   last  effect  is  produced,  is  the 

*  The  most  accurate  and  complete  description  of  the  anatomy  of  the  ear, 
is  that  given  by  Breschet,  Sur  les  Orp;anes  de  I'Onie,  which  first  appeared  in 
the  Annales  dns  Sciences  Naturelles,  xxix.  129.  [See,  also,  Breschet, 
Memoir,  de  I'Academie  de  Medecin.  torn.  v.  ;  and  Recherches  Anatomiqnes  et 
Physiologiqnes  sur  I'Orcrane  de  I'Ouie,  &c.,  Paris,  1836.]  A  compendious 
account  is  contained  in  Dr.  Roget's  Bridgewaler  Treatise,  ii.  420.  [Amer. 
edit.  ii.  305.     See,  also,  Dunglison's  Physiology,  3d  cit.  i.  141.] 


274 


SENSORIAL    FUNCTIONS. 


perilymph,  or  fluid  filling  the  cavities  of  the  labyrinth,  and  con- 
taining the  exquisitely  delicate  membrane  and  cretaceous  bodies 
which  the  extreme  fibrils  of  the  auditory  nerve  are  expanded. 
This  fluid  is  put  in  motion  by  the  air  in  the  cavity  of  the  tympa- 
num, and  thrown  into  corresponding  undulations. 

637.  The  accessory  parts  of  the  organ  of  hearing  may  there- 
fore be  divided  into  three  parts.  There  is,  first,  the  external  ear, 
which  is  an  elastic  cartilaginous  appendage  1o  the  organ,  curiously 
grooved,  so  as  to  form  a  series  of  parabolic  curves,  adapted  to 
receive  the  undulations  of  the  air,  and  convey  them  into  the 
passage  of  the  meatus  externus,  serving  apparently  an  office 
similar  to  that  of  the  expanded  part  of  a  trumpet.  The  sonorous 
undulations  are  thus  hiade  to  strike  against  the  membrane  of  the 
tympanum,  or  ear  drum,  which  is  stretched  across,  and  closes 
the  passage.  The  cavity  behind  this  membrane  is  filled  with  air, 
which  is  next  thrown  into  undulations  by  the  medium  of  the  ear- 
drum, the  vibrations  of  which  have  been  excited  by  those  of  the 
external  air.  In  order  to  preserve  an  equilibrium  between  the 
air  in  the  cavity  of  the  tympanum  and  the  external  air,  so  that 
the  membrane  may  not  sustain  a  greater  pressure  on  one  side 
than  on  the  other,  a  communication  is  kept  open  with  the  back 
part  of  the  throat  by  means  of  the  Eustachian  tube.  Hearing  is 
always  much  impaired,  if  from  any  cause  the  Eustachian  tube  is 
obstructed,  as  it  sometimes  is  by  a  common  cold,  which  then 
produces  a  temporary  deafness. 

638.  The  cavity  of  the  tympanum  is  of  a  very  singular  form, 
extending  into  the  mastoid  process  of  the  temporal  bone,  which 
has  a  cellular  structure.  A  chain  of  minute  bones,  the  ossicula 
auditus,  extends,  as  we  have  seen,  across  the  cavity,  terminating 
at  the  fenestra  ovalis,  or  aperture  leading  to  the  vestibule;  while 
another  aperture,  the  fenestra  rotunda,  also  closed  by  membrane, 
leads  to  one  of  the  spiral  turns  of  the  cochlea.  Thus,  the  fluid 
in  the  labyrinth  receives  from  the  impulse  made  on  these  two 
membranes,  which  are  situate  in  two  different  planes,  a  double 
undulation;  and  these  two  undulations,  the  one  circulating  along 
the  semicircular  canals,  the  other  through  the  spiral  turns  of  the 
cociilea,  probably  unite  at  some  focal  spot,  like  the  meeting  of 
two  tidal  waves,  and  increase  the  effect  produced.  These  undu- 
lations must  of  course  be  variously  modified,  according  to  their 
frequency,  and  the  order  of  their  succession,  and  the  impressions 
made  on  the  nerve  must  undergo  corresponding  modifications. 
But  we  are  so  completely  in  the  dark  as  to  the  real  office  of  the 
several  parts  of  this  elaborately  constructed  organ,  that  it  is 
exceedingly  difficult  to  prosecute  the  physiology  of  this  sense 
with  such  imperfect  data.  We  are  unable  even  to  form  a  rational 
conjecture  as  to  the  offices  of  the  delicate  muscles  provided  for 
directing  the  movements  of  those  ossicula,  which  are  articulated 


VISION.  275 

with  such  great  nicety,  and  which  seem  calculated  to  alter  the 
tension  of  the  niembrana  tympani,  and  bring  it  into  a  state 
capable  of  vibrating  in  unison  with  the  sonorous  undulations  that 
impinge  upon  it.  What  adds  in  no  small  degree  to  our  embar- 
rassment, is  the  knowledge  we  have  a.cquired  of  the  power  of 
hearing  being  retained,  without  apparent  diminution,  when  the 
greater  part  of  this  apparatus  of  bones,  with  their  joints  and 
muscles,  and  even  the  ear-drum  itself,  has  been  destroyed  by 
accident  or  disease.*  It  should  be  observed,  however,  as  Mr. 
Mayot  remarks,  that  the  stapes  is  so  strictly  applied  to  the 
membrane  of  the  fenestra  ovalis,  that  the  loss  of  this  bone 
necessarily  produces  incurable  deafness,  by  the  attendant  injury 
of  the  labyrinth. 

639.  Sir  Everard  Home  imagined  that  the  muscular  structure 
of  the  membrana  tympani,  enabling  it  to  contract  or  relax 
according  to  circumstances,  so  as  to  vibrate  in  unison  with  the 
musical  notes  which  reached  the  ear,  conferred  the  power  of 
distinguishing  musical  tones.  But  this  ingenious  hypothesis  is 
completely  overturned  by  the  fact  above  stated,  of  the  integrity 
of  the  membrane  of  the  tympanum  not  being  necessary  for  the 
perfect  accuracy  of  the  sense  of  hearing,  even  with  relation  to 
the  distinction  of  musical  sounds.  Dr.  Young  thinks  it  probable 
that  the  semicircular  canals  which  are  disposed  in  a  remarkable 
manner  in  three  orthogonal  planes,  corresponding  to  the  three 
dimensions  of  space,  enable  us  to  estimate  the  acuteness  or  pitch 
of  a  sound  ;  and  that  the  cochlea  serves  the  office  of  a  micro- 
meter of  sound. J  But  the  grounds  of  these  opinions  are  too 
vague  and  conjectural  to  inspire  us  with  any  confidence  in  their 
solidity.  When  the  external  passages  are  totally  obstructed,  sono- 
rous vibrations  may  still  be  transmitted  to  the  auditory  nerves 
by  means  of  the  bones  of  the  head.  Thus,  the  sound  of  a  tuning 
fork  applied  to  the  teeth,  or  even  to  other  parts  of  the  head,  is 
perfectly  audible  under  these  circumstances.  We  thus  possess  a 
criterion  for  determining,  in  cases  of  deafness,  whether  the  disease 
consists  in  the  insensibility  of  the  nerves  to  these  impressions,  or 
is  seated  in  the  passages  leading  to  the  labyrinth. 


Sect.  V. —  Vision. 

640.  The  physiology  of  the  eye  is  more  interesting  than  that 
of  any  of  the  other  organs  of  the  senses;  because,  from  the 
knowledge  we  possess  of  the  laws  of  optics,  to  which  it  is  so  admi- 

*  See  two  papers  by  Sir  Astley  Conper,  in  the  Philosophical  Transactions 
for  1800,  p.  151  ;  and  for  1801,  p.  437. 

f  Outlines  of  Human  Physiology,  3il  edition,  p.  221,  note. 
^  Medical  Literature,  p.  98  ;  and  Lectures,  vol.  i.  p.  387. 


276  SENSORIAL    FUNCTIONS. 

rably  adapted,  we  can  understand  the  offices  of  its  several  parts, 
and  the  mode  in  which  they  concur  in  the  production  of  the 
resulting  effect.  The  study  of  the  eye  has  been  said  to  be  the 
best  cure  for  atheism ;  and  it  furnishes,  indeed,  the  most  striking 
and  unequivpcal  proofs  .of  the  existence  of  design  and  intelli- 
gence in  the  construction  of  the  animal  fabric.  These  proofs 
have  accordingly  been  always  amongst  those  most  prominently 
adduced  by  philosophers  in  support  of  the  arguments  of  natural 
theology. 

641.  The  organs  subservient  to  vision  are  lodged  securely  in 
bony  cavities  of  the  orbits,  where  the  surrounding  bones  protect 
them  on  every  side,  excepting  in  front.  They  may  be  divided 
into  the  internal  and  the  external  parts;  the  former  consisting 
of  the  spherical  bodies  denominated  ihe  globes  of  the  eye,  or  eye- 
halls  ;  and  the  latter  comprising  parts  which  give  motion  to  the 
globe,  and  otherwise  assist  it  in  its  functions. 

1.  Internal  Parts  of  the  Eye. 

642.  The  eye-ball  is  composed  of  segments  of  two  unequal 
spheres  ;  one  of  which,  constituting  about  four-fifths  of  the  whole, 
forms  the  portion  which  is  in  the  orbit ;  while  the  other  fifth  is 
that  part  which  is  seen  in  front,  and  which,  being  a  portion  of  a 
smaller  sphere,  is  more  protuberant.  The  diameter  of  the  eye- 
ball, from  behind  forwards,  is  accordingly  longer  than  its  trans- 
verse diameter;  the  proportion  being  that  of  twenty-five  to 
twenty-three. 

643.  The  eye-ball  is  made  up  of  coats  and  humours.  The 
former  consists  of  the  sclerotica,  cornea,  choroides,  and  retina, 
together  with  the  conjunctiva.  Of  the  latter  there  are  three,  viz. 
the  vitreous,  crystalline,  and  aqueous  humours. 

644.  The  sclerotica,  which  is  the  exterior  coat,  is,  from  its 
compact  fibrous  texture,  the  densest  and  strongest,  as  well  as  the 
thickest  of  the  tunics  of  the  eye,  and  the  one  from  which  the 
other  parts  of  the  eye-ball  derive  their  principal  support.  It 
covers  all  that  portion  of  the  globe  of  the  eye,  which  has  already 
been  pointed  out  as  constituting  its  largest  segment.  At  its  ante- 
terior  edge  it  is  joined  to  the  more  convex  tunic,  which  com- 
pletes the  figure,  and  is  named  the  cornea,  from  its  being  com- 
posed of  a  great  number  of  concenti'ic  lamina,  of  a  horny  elastic 
texture.  Some  authors  have  given  it  the  name  of  the  cornea 
incida,  from  its  perfect  transparency,  and  by  way  of  contrast  to 
the  sclei'otica,  which  they  had  named  the  cornea  opaca. 

645.  The  choroid  coat,  or  tunica  choroides,  lies  immediately 
within  the  sclerotica,  and  is  composed  of  a  congeries  of  blood- 
vessels connected  together  by  membrane.  It  has  been  distin- 
guished into  tvvro  layers,  the  innermost  of  which  has  been  termed 


INTERNAL    PARTS    OF    THE    EYE.  277 

the  tunica  Ruyschiana.  At  the  middle  of  the  choroid  coat  are 
observed  numerous  vessels  convoluted  into  a  spiral  form.  These 
have  been  termed  the  vencB  vorticosce.  The  interna]  surface  of  the 
tunica  Ruyschiana,  or  tapetum,  as  it  has  been  called,  seems,  from 
its  villous  or  fleecy  appearance,  to  be  a  secreting  surface.  It  is 
everywhere  lined  with  a  black  or  deep-brown  mucous  substance, 
included  in  a  fine  cellular  tissue.  This  is  \he  pigmentum  nigrum, 
which  forms  a  laver,  separating  the  choroides  from  the  next 
coat,  or  retina.  This  latter  tunic  is  an  expansion  of  the  pulpy 
substance  of  the  optic  nerve,  spread  over  a  fine  membrane.  The 
optic  nerve,  from  which  this  medullary  matter  is  derived,  enters 
the  eye  at  its  back  part,  at  a  point  nearer  to  the  nose  than  the 
centre,  or  axis  of  the  eye,  and  perforates  the  sclerotic  and 
choroid  coats. 

646.  From  the  inner  margin  of  the  junction  of  the  cornea  and 
sclerotica,  there  extends  across  the  fore  part  of  the  globe  of  the 
eye  a  membranous  partition,  called,  from  the  variety  of  its  colour, 
the  iris;  it  is  perforated  in  the  centre  by  an  aperture,  called  the 
pupil,  because,  as  it  is  said,  it  represents  objects  no  larger  than 
a  pupilla,  or  puppet.  The  structure  of  the  iris  is  exceedingly 
peculiar:  it  appears  to  be  made  up  of  a  number  of  fibres,  which 
pass  from  the  inner  to  the  outer  margin  in  a  radiated  direction, 
together  with  others  W'hich  run  circularly.  These  fibres  have 
been  presumed  to  be  of  a  muscular  structure ;  but  doubts  are 
still  entertained  with  regard  to  this  point.  The  posterior  surface 
of  the  iris  is  lined  wdth  a  pigment  similar  to  that  which  is  found 
W'ithin  the  choroid  coat.  It  has  been  called  the  uvea,  from  its 
fancied  resemblance  in  colour  to  the  grape. 

647.  The  iris  is  connected  with  the  choroid  coat  by  an  inter- 
mediate structure,  called  the  ciliary  ligaments,  ciliary  circle,  or 
orhiculus  ciliaris,  which  is  a  circular  belt,  more  than  a  line  in 
breadth,  made  up  of  a  soft  and  pulpy  tissue,  and  of  a  whitish 
colour.  It  is  at  this  part  that  the  choroides  adheres  firmly  to 
the  sclerotica.  From  this  part,  also,  there  extends  inwards  a 
dark  coloured  ring,  which  is  a  continuation  of  the  choroides,  and 
is  termed  the  c&rpus  ciliare.  It  is  about  the  sixth  part  of  an  inch 
in  breadth  towards  the  temple,  but  somewhat  narrower  towards 
the  nose.  It  is  covered  in  every  part  by  the  pigmentum  nigrum. 
It  is  marked  by  radiated  striae  at  its  inner  part,  but  they  are 
somewhat  obscured  by  the  pigmentum  nigrum.  At  the  outer  part 
these  striffi  become  gradually  broader  and  more  elevated,  and 
appear  like  folds,  only  the  intervals  between  them  being  covered 
with  the  pigment.  These  folds  are  termed  the  ciliary  processes. 
Each  of  these  processes  is  of  an  irregular  triangular  figure,  with 
the  base  outwards,  or  at  the  ciliary  circle,  and  its  apex  inwards, 
or  towards  the  axis  of  the  eye.  Their  number  is  generally  about 
sixtv,  and  they  are  alternately  longer  and  shorter. 

24 


278  SENSORIAL    FUNCTIONS. 

648.  About  three-fourths  of  the  globe  of  the  eye,  within  these 
several  tunics,  is  filled  by  a  very  transparent  and  gelatinous 
humor,  which,  from  its  supposed  resemblance  to  melted  glass,  has 
been  termed  the  vitreous  humor.  It  is  nearly  of  the  consistence 
of  the  white  of  an  egg,  and  consists  of  a  fluid  substance  con- 
tained in  the  cells  of  a  very  fine  and  delicate  cellular  tissue, 
called  the  hyaloid  membrane.  It  is  invested  by  a  transparent 
ntiembrane,  termed  the  tunica  vitrea,  or  capsule  of  the  vitreous 
humors.  The  anterior  surface  of  the  vitreous  humor  is  de- 
pressed, for  the  lodgment  of  the  crystalline  lens,  or  humor,  which 
is  a  dense  body,  perfectly  transparent,  and  has  the  shape  of  a 
double  convex  lens,  of  which  the  posterior  surface  has  a  greater 
convexity  than  the  anterior  surface.  The  lens  is  composed  of  a 
great  number  of  concentric  laminse,  which  become  more  and  more 
dense  towards  the  centre,  and  each  lamina  is  made  up  of  very 
distinct  parallel  fibres.  It  is  enclosed  in  its  own  peculiar  capsule, 
in  which  it  appears  to  float  loosely,  a  watery  fluid,  called  the 
liquor  Morgagni,  being  interposed. 

649.  The  fore  part  of  the  eye-ball,  between  the  crystalline  lens 
and  the  cornea,  is  filled  by  a  watery  fluid,  called  the  aqueous 
humor,  in  the  middle  of  which  the  iris  is  suspended,  thus  dividing 
the  space  into  what  are  called  the  anterior  and  posterior  chambers 
of  the  aqueous  humor.  The  aqueous  humor,  like  the  other  humors, 
is  contained  within  a  dehcate  membrane,  which  fines  the  inside 
of  the  cornea,  and  passes  over  the  crystalline  lens  and  the  convex 
margin  of  the  vitreous  humor. 

650.  The  capsule  of  the  lens  adheres  closely  to  the  tunica 
vitrea.  Behind  the  edge  of  the  former,  and  between  the  margin 
of  the  ciliary  zone  and  capsule  of  the  vitreous  humor,  a  triangular 
passage  is  formed,  called,  from  its  discoverer,  the  circle  of  Petit, 
or  canalis  Petitianus.  When  air  is  blown  into  this  passage,  it 
passes  freely  round  the  edge  of  the  lens. 

651.  At  that  part  of  the  retina  which  is  situate  in  the  axis  of 
the  eye,  there  is  a  small  circle,  where  the  retina  is  transparent, 
giving  rise  to  the  appearance  of  a  hole,  as  if  the  retina  were 
deficient  in  that  part.  It  was  discovered  by  S3mmerring,  and 
bears  the  name  of  the  foramen  centrale  of  Sommerring.  It  is 
surrounded  by  a  yellow  circle,  about  a  line  in  diameter.  The 
fibres  of  the  optic  nerve,  in  passing  to  form  the  retina,  per- 
forate a  thin  plate  of  membrane  which  is  extended  from  the 
sclerotica,  and  which  is  termed  the  lamina  cribrosa.  The  centre 
of  the  optic  nerve  is  perforated  by  the  arteria  centralis  reiince, 
forming  an  aperture  which  has  been  called  the  porus  opticus. 

2.  External  Parts  of  the  Eye. 

652.  The  orbit  is  a  conical  cavity,  in  the  fore  part  of  which 
the  globe  of  the  eye  is  situate,  the  remaining  space  behind  the 


EXTERNAL    PARTS    OF    THE    EYE.  279 

globe  being  chiefly  filled  with  fat,  which  surrounds  the  optic 
nerve,  and  intervenes  between  it  and  the  straight  muscles,  that 
extend  between  the  margin  of  the  foramen  opticum,  through 
which  the  optic  nerve  passes  out  of  the  skull,  and  the  fore  part 
of  the  sclerotic  coat,  where  they  are  inserted  by  broad  and  flat 
tendons.  These  tendinous  expansions  have  been  improperly  con- 
sidered as  composing  one  of  the  tunics  of  the  eye,  which  being 
of  a  white  colour,  has  received  the  name  of  tunica  alhuginea. 

653.  The  globe  of  the  eye  is  covered  at  the  fore  part  by  two 
eye-lids  or  palpebrcB,  which  are  composed  of  muscular  fibres, 
covered  by  the  common  integuments,  supported  at  their  edge  by 
a  cartilage  called  the  tarsus,  and  furnished  with  a  row  of  hairs, 
termed  cilia,  or  eye-lashes.  At  the  roots  of  the  eye-lashes  are 
sebaceous  follicles,  named  from  the  anatomist  who  first  observed 
them,  the  glandulcB  Meibomii,  and  which  secrete  a  glutinous  lini- 
ment. The  eye-lids  are  lined  on  their  interior  surface  by  a  very 
fine  and  smooth  serous  membrane,  which  is  reflected  over  the 
anterior  part  of  the  globe  of  the  eye,  and  even  over  the  surface 
of  the  cornea.     This  membrane  is  called  the  tunica  conjunctiva. 

654.  Between  the  ball  of  the  eye  and  the  upper  vault  of  the 
orbit,  on  the  temporal  side,  lies  the  lacrymal  gland,  which 
secretes  the  tears.  It  is  composed  of  a  number  of  small,  whitish, 
granular  bodies,  which  are  collected  together  into  two  lobes. 
There  is  also  a  chain  of  smaller  glands  lying  between  the  prin- 
cipal gland  and  upper  eye-lid,  and  connecting  them  together. 
The  excretory  ducts  from  all  these  glands  are  exceedingly  mi- 
nute, and  terminate  in  the  inner  surface  of  the  upper  eye-lid,  near 
the  outer  angle  of  the  eye.  After  moistening  the  surface  of  the 
eye,  the  tears  are  again  collected  by  tw^o  small  orifices,  called 
the  puncta  lacrymalia,  placed  on  a  small  eminence  in  each  eye- 
lid, near  the  inner  angle  of  the  eye,  at  the  extremity  of  the  tarsus. 
They  are  the  beginnings  of  two  small  canals  that  run  in  the 
direction  of  the  edges  of  the  eye-lids,  towards  the  side  of  the 
nose,  where  they  approach  each  other,  and  terminate  together  in 
the  lacrymal  sac,  v^hich  is  a  membranous  bag  situate  on  the  os 
unguis,  and  leading  to  a  passage  into  the  cavity  of  the  nostrils. 
The  puncta  are  kept  separate  by  the  interposition  of  a  small 
reddish  body,  called  the  caruncula  lacrymalis,  situate  between 
the  inner  angle  of  the  eye-lids  and  the  ball  of  the  eye.  Minute 
hairs  are  found  upon  the  surface  of  this  body,  which  serve  to 
entangle  small  objects  which  might  otherwise  get  into  the  eye. 
There  is  also  a  reduplication  of  the  tunica  conjunctiva,  shaped 
like  a  crescent,  and  hence  termed  the  valvula  semilunaris,  the 
points  of  ,which  are  directed  towards  the  puncta,  and  which 
assists  the  caruncle  in  directing  the  tears  to  the  puncta. 

Having  thus  described  the  apparatus  for  vision,  we  shall  now 
proceed  to  consider  the  mode  in  which  that  function  is  performed. 


280  SENSORIAL    FUNCTIONS. 

3.  Optical  Principles. 

655.  The  object  of  this  sense  is  to  convey  to  us  a  knowledge 
of  the  existence  and  visible  qualities  of  distant  objects,  by  means 
of  the  light  which  they  send  to  the  eye.  This  is  accomplished 
by  altering  the  natural  direct  course  of  these  rays,  so  that  they 
may  form  a  distinct  image  of  these  objects  on  the  retina.  That 
such  images  are  actually  formed  on  the  retina  may  be  easily 
shown  in  the  eye  of  an  animal  recently  killed,  by  carefully  re- 
moving the  opaque  sclerotic  and  choroid  coats,  together  with  the 
black  pigment  from  the  back  of  the  eye,  so  as  to  expose  the 
retina.  The  objects  on  the  other  side,  in  front  of  the  cornea,  will 
then  be  seen  beautifully  depicted  on  the  retina,  their  images  being 
inverted ;  precisely  in  the  same  way,  and  on  the  same  principles 
as  they  are  seen  in  a  simple  camera  obscura. 

656.  In  order  to  understand  and  trace  the  operation  of  the  prin- 
ciples concerned  in  these  phenomena,  it  will  be  necessary  to 
refer  to- the  laws  of  optics. 

The  rays  of  light  in  traversing  any  medium  of  uniform  density, 
move  always  in  straight  lines;  but  when  the  density  changes  they 
deviate  somewhat  irom  this  rectilinear  course,  according  to  the 
direction  of  the  ray  with  respect  to  the  planes  in  which  the  change 
of  density  occurs.  Thus  a  ray  from  the  sun,  or  other  celestial 
body,  traversing  obHquely  through  our  atmosphere,  the  different 
strata  of  which  are  of  increasing  density  as  they  come  nearer 
to  the  earth,  is  gradually  bent  in  its  course,  and  arrives  at  the 
surface  of  the  earth  in  a  direction  somewhat  nearer  to  a  perpen- 
dicular line  than  if  there  had  been  no  atmosphere.  This  deflexion 
from  a  straight  line  is  termed  refraction.  Refraction  takes  place 
suddenly,  if  the  ray  passes  abruptly  from  one  medium  to  another, 
which  sensibly  differs  from  it  in  its  density ;  the  direction  of 
the  deflexion  being  always  towards  the  denser  medium  ;  or,  to 
speak  more  accurately,  towards  a  line  drawn  perpendicular  to 
the  surface  common  to  the  two  media,  and  situate  in  the  denser 
medium. 

657.  In  the  case  of  the  passage  of  a  ray  through  the  surface 
of  a  new  medium  of  very  different  density  from  the  first,  another 
phenomenon  takes  place  ;  the  ray  is  decomposed,  part  being  trans- 
mitted and  refracted,  while  another  portion  is  turned  completely 
back  into  the  medium  it  was  already  traversing.  This  is  termed 
reflexion.  Objects  which  are  not  luminous  in  their  own  nature 
are  rendered  visible  only  by  the  reflexion  from  their  surfaces  of 
the  light  which  ihey  receive  from  other  bodies.  The  law  in  this 
case  is,  that  the  angle  of  reflexion,  by  which  is  meant  the  angle 
which  the  course  of  the  reflected  ray  makes  with  a  line  perpen- 
dicular to  the  surface,  is  equal  to  the  angle  of  incidence,  or  the 
angle  which  the  incident  ray  makes  with  that  same  perpendicular; 


FORMATION   OF    IMAGES    IN   THE    EYE.  281 

and  also,  that  it  is  in  the  same  plane  with  the  incident  ray,  and 
the  perpendicular  hne.* 

658.  The  law  of  refraction  is,  that  the  course  of  the  refracted 
ray  is  deflected  towards  that  part  of  the  perpendicular  which  is 
situate  in  the  denser  medium,  and  tiiat  the  sine  of  the  angle  of 
refraction,  (or  the  angle  it  makes  with  the  perpendicular)  has  to 
the  sine  of  the  angle  of  incidence  the  same  constant  ratio.  This 
ratio  increases  in  proportion  to  the  difference  there  is  between 
the  two  media  in  respect  of  density. 

4.  Formation  of  Images  in  the  Eye. 

659.  It  follows  as  a  consequence  of  the  above  laws,  that  a 
pencil  of  rays  proceeding  through  the  air,  and  falling  on  the 
convex  spherical  surface  of  a  medium  of  greater  density  than  the 
air,  (as  is  the  case  with  the  cornea  of  the  eye,)  is  so  refracted 
as  to  be  collected,  after  proceeding  a  certain  distance,  into  one 
and  the  same  point.  This  will  readily  appear  when  we  consider 
that  those  rays  fall  with  more  obliquity  on  the  cornea,  according 
as  they  are  more  distant  from  the  central  ray  of  the  pencil,  or 
that  which  may  be  conceived  to  fall  perpendicularly  on  its  sur- 
face. These  more  oblique  rays  are  consequently  more  refracted ; 
that  is,  more  bent  from  their  original  course  ;  and  this  law  being 
observed  throughout  the  whole  pencil,  all  the  rays  will  tend 
after  refraction  to  the  same  point,  which  point  is  called  ihejocus 
of  that  pencil  of  rays. 

660.  The  same  process  taking  place  with  regard  to  all  the 
other  pencils  of  rays  proceeding  respectively  from  the  several 
points  of  the  objects  viewed,  and  each  being  collected  into  sepa- 
rate points  in  different  parts  of  the  retina  which  receives  them, 
images  of  those  objects  will  be  delineated  on  that  membrane  ; 
for  it  is  evident  that  all  the  focal  points  will  have,  with  respect 
to  one  another,  the  same  relative  positions  as  the  points  of  the 
external  objects  from  which  each  pencil  of  rays  proceeds,  when 
referred  to  the  sphere  of  vision.     The  impression  thus  made  on 

*  [Some  interesting  points  of  diagnosis  are  connected  with  the  reflection 
which  takes  place  from  the  humors  of  the  eye.  If  a  lighted  candle  be  held 
before  an  eye,  the  pupil  of  which  has  been  dilated,  and  in  which  there  is  no 
obscurity  in  the  humors  or  their  capsules,  three  distinct  images  of  the  flame 
are  perceptible — two  upright  and  one  inverted ,-  one  of  the  former  being  re- 
flected from  the  cornea,  and  the  other  from  the  anterior  part  of  the  crystalline 
lens  ;  the  last  inverted  image  being  caused  by  the  reflection  from  the  posterior 
concave  surface  of  the  crystalline.  Mr.  Sanson  has  proposed  this  "catoptric 
method"  of  examining  the  eye  as  a  means  of  diagnosis  between  cataract  and 
amaurosis  ;  and  Dr.  Hays,  who  has  employed  it  to  some  extent,  regards  it  as 
a  most  valuable  mode  of  investigating  various  conditions  of  the  eye,  which 
might  not  be  readily  understood  without  its  agency.  See  Mr.  Sanson,  cited  in 
Amer.  Journal  of  the  Med.  Sciences,  August,  18,38,  p.  4,94*  aod  Dr.  Hays,  Ibid,. 
May,  1839,  p.  255,1 

54* 


282  SENSORIAL    FUNCTIONS. 

each  respective  point  of  the  retina,  is  transmited  to  the  sensorium, 
where  it  makes  a  distinct  impression,  and  gives  rise  to  the  sen- 
sation ofUght  and  colour;  and  in  conjunction  with  the  experience 
gradually  gathered  from  the  sense  of  touch,  imparts  to  us  a 
knowledge  of  the  existence,  relative  situation,  form,  magnitude, 
distance,  and  colour  of  the  objects  before  as.  This,  then,  is 
vision. 

661.  Such  is  the  general  outline  of  the  mode  in  which  vision 
is  accomplished;  but  there  are  a  thousand  beautiful  contrivances 
and  adjustments  provided  for  ensuring  the  accuracy  with  which 
this  picture  of  the  surrounding  scene  is  portrayed  on  the  retina. 
The  perfection  of  vision  is  entirely  dependent  on  the  distinctness, 
the  vividness,  and  the  fidelity  of  this  picture;  and  the  whole 
apparatus  of  the  eye  is  calculated  to  obtain  these  qualities. 

662.  The  purposes,  served  by  the.  apparatus  external  to  the 
globe  of  the  eye,  are  sufficiently  obvious.  The  effectual  pro- 
tection given  to  the  eye  by  the  arched  form  of  the  bones  which 
compose  the  orbit, — the  provision  of  a  soft  cushion  in  the  fat 
which  occupies  the  bottom  of  the  cavity, — the  beautiful  con- 
trivance of  the  eye-lids,  which,  on  the  least  appearance  of  danger, 
are  ever  ready  to  close  upon  the  organs  they  are  appointed  to 
guard, — and  even  the  direction  of  the  eye-brows,  intended  to 
divert  the  course  of  the  perspiration  from  the  forehead,  are  all 
calculated  to  call  forth  our  admiration,  because  the  end  to  be 
answered  being  obvious,  we  can  judge  of  the  fitness  of  the  means 
for  the  accomplishment  of  those  ends.  A  still  further  proof  of 
exquisite  design  offers  itself  in  the  lacrymal  apparatus,  which 
provides  the  means  of  preserving  the  surface  of  the  cornea 
always  clean  and  transparent,  and  fitted  for  its  office  of  regu- 
larly refracting  the  rays  of  light. 

663.  The  humors  of  the  eye,  through  which  the  light  passes 
before  arriving  at  the  retina,  have  different  degrees  of  density, 
and  consequently  have  different  degrees  of  refractive  power. 
The  first  and  greatest  refraction  of  the  rays  takes  place  at  the 
outer  surface  of  the  cornea  ;  the  next  is  at  the  inner  surface, 
where  the  rays  meet  with  the  aqueous  humor.  Now  this  humor 
is  rather  less  dense  than  the  cornea,  and  consequently  the  rays 
already  refracted,  and  rendered  convergent  by  the  cornea,  have 
their  convergence  slightly  diminished,  when  they  traverse  the 
aqueous  humor.  These,  in  fact,  are  converging  towards  points 
at  some  distance  beyond  the  retina.  The  iris  is  interposed  in  the 
course  of  the  rays  while  they  are  passing  through  the  aqueous 
humor ;  the  circular  aperture  of  this  membrane,  the  pupil,  admit- 
ting only  the  more  central  portion  of  each  pencil  of  rays.  By 
intercepting  the  extreme  rays,  which,  in  consequence  of  a  pecu- 
liarity in  the  law  of  spherical  refraction,  hereafter  to  be  explained, 
would,  if  allowed  to  reach  the  retina,  somewhat  confuse  the 


CORRECTION  OF  ABERRATION.  283 

image,  greater  clearness  of  that  image  is  obtained,  at  the  sacri- 
fice, indeed,  of  a  portion  of  brightness.  It  serves,  accordingly, 
the  same  purpose  with  regard  to  the  eye,  which  the  circular 
ring,  placed  in  the  interior  of  a  telescope,  effects  in  contracting 
the  aperture  of  the  instrument;  rendering  the  image  more  dis- 
tinct, though  less  illuminated  than  it  would  otherwise  be.  But 
the  iris  has  this  great  superiority  over  the  circle  in  the  telescope, 
inasmuch  as  it  is  capable  by  its  contractile  power  of  enlarging 
or  diminishing  the  aperture  of  the  pupil,  as  occasion  requires. 
Thus,  when  the  object  viewed  is  but  faintly  illuminated,  the  pupil 
is  enlarged,  and  admits  more  light,  thus  giving  greater  bright- 
ness to  the  picture;  an  advantage  which  more  than  compensates 
for  the  slight  indistinctness  of  the  fainter  images  composing 
that  picture.  When,  on  the  contrary,  an  object  is  too  bright,  so 
that  its  image  would  produce  too  vivid  an  impression  on  the 
retina,  the  pupil  immediately  contracts,  so  as  to  reduce  the 
quantity  of  light  admitted  into  the  interior  of  the  eye,  and  to 
prevent  any  injurious  effect  upon  the  retina. 

5.  Adjustments  for  the  Correction  of  Aberration. 

664.  That  part  of  the  converging  pencil  of  rays,  which  is  admit- 
ted through  the  pupil,  falls  upon  the  anterior  convex  surface  of 
the  crystalline  lens,  which  being  denser  than  the  aqueous  humor, 
occasions  a  new  refraction  of  the  rays,  and  gives  them  an  increased 
degree  of  convergence,  so  that  they  now  tend  to  foci  nearer  to  the 
retina  than  before,  though  still  somewhat  beyond  it. 

665.  An  exquisite  provision  is  found  in  the  peculiar  structure 
of  the  lens  for  correcting  what  is  termed  the  spherical  aberration. 
It  is  a  necessary  consequence  of  the  mathematical  law  of  refrac- 
tion, that  in  a  pencil  of  rays  falling  on  the  convex  spherical  surface 
of  a  denser  medium,  those  rays  which  are  farthest  from  the  cen- 
tral ray,  will  be  bent  somewhat  more  than  is  requisite  to  bring 
them  to  the  same  focal  point  as  the  rays  which  are  nearer  to  the 
centre  of  the  pencil ;  hence  all  the  rays  can  never  be  collected 
accurately  into  the  same  point ;  although  in  ordinary  optical  instru- 
ments, such  as  com.mon  telescopes,  and  camera  obscura,  the  aber- 
ration thus  resulting  is  confined  within  such  narrow  limits  as  not 
to  produce  any  very  great  inconvenience.  But  in  the  eye  even 
this  minute  defect  of  ordinary  optical  instruments  is  remedied. 
The  lens  is  composed  of  successive  lamina;,  increasing  in  their 
density  and  refractive  power,  in  proportion  as  they  approach  the 
centre ;  that  central  part  being  the  hardest  and  densest  of  the 
whole.  The  central  rays  of  each  pencil,  therefore,  are  subjected 
to  a  greater  refractive  action  than  the  more  exterior  rays,  and  the 
whole  are  brought  accurately  to  convergence  at  the  same  focal 
point. 


284  SENSORIAL    FUNCTIONS. 

666.  After  passing  through  the  crystalline  lens,  the  rays  enter 
the  vitreous  humor,  where,  again,  there  is  a  change  of  density  in 
the  nnedium.  The  density  of  the  vitreous  humor  is  less  than  that 
of  the  lens  ;  and  were  its  surface  convex,  the  convergence  of  the 
rays  would  be  diminished  by  the  refraction  they  would  then  expe- 
rience ;  but  the  surface  being  concave,  the  refraction  contributes 
still  farther  to  increase  the  convergence  of  the  rays,  which  now 
traverse  the  aqueous  humor,  and  are  collected  accurately  into 
their  respective  foci  on  the  retina  itself 

667.  Rays  proceeding  from  objects  at  different  distances  from 
the  eye,  will  arrive  at  the  cornea  with  different  degrees  of  diver- 
gence, and  the  same  refractive  powers  of  the  humors  would  cause 
them  to  converge  at  different  distances ;  in  order,  therefore,  to 
obtain  distinct  images  of  these  objects  on  the  i^etina,  either  the 
distance  of  that  membrane  from  the  cornea  must  be  altered,  or 
the  refractive  power  of  the  humors  must  be  changed.  Thus,  if 
the  power  of  the  eye  at  any  one  time  be  suited  to  distinct  vision 
of  distant  objects,  near  objects  will  appear  confused,  from  the 
indistinctness  of  their  images  on  the  retina ;  because  the  focus  of 
convergence  of  the  rays  proceeding  from  those  objects  is  farther 
back  than  the  situation  of  the  retina.  If,  either  by  elongating  the 
axis  of  the  eye,  the  retina  could  be  removed  to  this  new  focal 
distance,  or  else  by  increasing  the  refractive  power  of  the  humors, 
the  rays  could  be  made  more  convergent  than  before,  we  should 
again  obtain  distinct  images  of  those  near  objects  on  the  retina  ; 
but  then  the  images  of  distant  objects  would,  at  the  same  time, 
and  from  the  contrary  cause,  be  indistinct ;  and  in  order  to  give 
distinctness  to  these,  the  contrary  changes  are  required  to  be  made 
in  the  eye  to,  those  already  mentioned.  Now,  it  is  found  that 
the  eye  really  possesses  the  power  of  accommodation  here  des- 
cribed, adapting  itself,  by  some  internal  changes,  to  the  vision  of 
both  near  and  remote  objects,  according  as  the  attention  is  directed 
respectively  either  to  the  one  or  to  the  other. 

668.  The  effort  by  which  the  eye  changes  its  internal  state,  so 
as  to  accommodate  its  powers  to  the  vision  of  near  objects,  after 
having  viewed  those  more  distant,  is  always  attended  with  a 
contraction  of  the  pupil;  and  the  exclusion  of  the  remoter  rays, 
consequent  upon  this  diminution  of  aperture,  must  partly  contri- 
bute to  the  greater  distinctness  of  the  images,  by  excluding  the 
rays  near  the  circumference  of  each  pencil.  But  it  is  certain 
that  the  refractive  powers  of  the  eye  are  also  increased ;  and  it 
is  a  question  of  considerable  difficulty  to  determine  the  manner 
in  which  this  increase  is  effected.  Sir  Everard  Home*  supposed 
that  it  was  accomplished  by  the  joint  actions  of  the  straight  mus- 

*  See  Philosophical  Transactiohs  for  1794,  p.  ^l;  1795,  p.  I;  1796,  p.  }; 
1797,  p.  1. 


CORRECTION  OF  ABERRATION. 


285 


cles  which  surround  the  ball  of  the  eye,  and  which,  by  compress- 
ing it  all  round  its  sides,  might  elongate  its  axis  and  increase  the 
distance  of  the  retina  from  the  cornea,  while  they  at  the  same 
time  would  make  the  cornea  more  convex,  by  drawing  back 
its  circumference,  and  thus  rendering  its  central  part  more 
protuberant.  This  plausible  theory  is  overturned  by  the  fact 
discovered  by  Dr.  Young,*  that  when  the  efiect  of  any  change 
in  the  curvature  of  the  cornea  is  removed  by  placing  the  eye 
under  water,  the  eye  still  retains  its  power  of  accommodation  to 
the  vision  of  objects  at  different  distances,  by  changes  which  take 
place  in  its  refractive  powers. 

669.  The  most  probable  supposition  relative  to  this  operation 
is,  that  the  ciliary  ligament  has  the  power  of  contracting  at  the 
same  time  with  the  sphincter  of  the  iris ;  a  change  which  will 
be  attended  with  the  effect  of  bringing  the  lens  somewhat  for- 
wards, and  of  increasing  the  convexity  of  its  surfaces,  while  the 
convexity  of  the  cornea  will  also  be  increased.  Any  cause  which 
produces  the  contraction  of  the  pupil,  such  as  a  bright  light, 
enables  the  eye  to  adjust  itself  more  rapidly  to  vision  at  a  shorter 
distance ;  and,  on  the  contrary,  the  suspension  of  this  power  of 
contraction  of  the  circular  fibres  of  the  iris,  occasioned  by  bella- 
donna, is  accompanied  by  the  total  but  temporary  loss  of  this 
power  of  adjustment.  Those  who,  by  frequent  practice  in  expe- 
rimenting on  their  own  eyes,  have  acquired  a  considerable  volun- 
tary power  of  changing  the  refracting  condition  of  the  eye,  even 
although  there  be  no  object  before  the  field  of  vision  requiring 
such  change,  when  they  exert  this  power,  also  contract  the  pupil, 
which  by  this  means  indirectly  acquire  the  character  of  a  volun- 
tary muscle ;  although  in  other  respects,  and  with  other  persons, 
it  is  strictly  to  be  ranked  in  the  class  of  the  involuntary  muscles. 
The  writer  of  this  treatise  possesses  this  power,  and  has  given  an 
account  of  the  circumstances  attending  its  exertion  in  a  letter  to 
Mr.  Travers.f 

670.  The  same  gradation  of  density  in  the  successive  lamina? 
of  the  crystalline  lens,  and  the  consequent  successive  refractions 
of  the  rays  effected  by  the  several  humors  of  the  eye,  have  also 
the  effect  of  correcting  the  dispersion  of  light,  arising  from  the 

*  Ibid,  for  1793,  p.  169  ;  and  for  1801,  p.  53. 

I  Contained  in  the  sketch  of  the  Physiology  of  the  Eye,  prefixed  to  Mr. 
Travers'  Synopsis  of  the  Diseases  of  the  Eye  and  their  Treatment,  p.  72. 

[It  is  very  doubtful  whether  such  power  of  adaptation  really  exists.  Magen- 
die's  opinion  (Precis  Elementaire,  i.  72,  2de  ^dit.)  is  decidedly  in  the  negative ; 
and  the  late  Dr.  Fletcher  (Rudiments  of  Physiology,  Part  3,  p.  48,  Edinb. 
1837),  after  alluding  to  the  various  hypotheses  on  the  subject,  adds  :  "It 
appears  absurd  to  atlempt  to  explain  a  fact  which  has  no  real  existence, 
since  it  has  never  been  proved  that  the  eye-ball  has  any  capability  of  adapt- 
ing itself  to  different  distances,  or  that  any  such  adaptation  is  required." 
See,  on  all  this  subject,  Dunglison's  Physiology,  3d  edit.  i.  219.] 


286  SENSORIAL    FUNCTIONS. 

difference  in  refrangibility  of  the  differently  coloured  rays.*  The 
eye,  in  addition  to  its  other  perfections,  has  the  properties  of  an 
achromatic  optical  instrument,  correcting  the  confusion  of  colour 
in  the  images  it  forms  on  the  retina. 

671.  All  extraneous  Hght,  which  might  be  reflected  from  one 
part  of  the  eye  to  another,  and  might  be  mixed  with  the  rays 
which  should  exclusively  form  the  image  on  the  retina,  is  ab- 
sorbed by  means  of  the  pigmentum  nigrum,  which  is  placed 
immediately  behind  the  retina,  which  lines'  every  part  of  the  in- 
terior of  the  eye,  and  which  extends  over  the  cihary  circle,  and 
over  the  posterior  surface  of  the  iris. 

672.  Different  parts  of  the  retina  possess  different  degrees  of 
sensibility ;  the  centre,  or  that  situate  in  the  axis  of  the  eye  as  it 
is  called,  immediately  opposite  to  the  pupil,  being  by  far  the  most 
sensible  part.  We  accordingly  see  most  distinctly  those  objects, 
the  images  of  which  are  formed  on  that  spot.  Hence,  whenever 
we  pay  attention  to  an  object,  we  immediately  direct  both  eyes 
towards  it  in  such  a  manner  as  that  the  centre  of  both  retinae 
may  receive  its  image.  It  is  very  remarkable  that  there  is  a  mi- 
nute circular  space  situate  exactly  in  the  axis  of  the  eye,  where 
the  retina  seems  to  be  deficient,  so  as  to  produce  the  appearance 
of  a  perforation  at  the  very  point  where  vision  is  most  distinct. 
No  satisfactory  explanation  of  this  curious  circumstance  has  yet 
been  given. 

673.  When  the  eye  is  at  rest,  the  field  of  distinct  vision  is  very 
limited  ;  it  extends,  however,  according  to  Dr.  Young,  to  a  space 
formed  by  a  radius  of  about  60  or  70  degrees ;  it  extends  to  a 
greater  distance  outwards  than  inwards,  being  90  degrees  in  the 
former  direction,  and  only  60  degrees  in  the  latter.  It  extends 
downwards  70  degrees,  and  only  50  degrees  upwards. 

674.  Mariotte,-)-  of  the  French  Academy  of  Sciences,  made  the 
curious  discovery  that  there  is  a  part  of  the  retina  situate  at  the 
termination  of  the  optic  nerve  which  is  insensible  to  light ;  so 
that  when  the  image  of  any  object  falls  upon  that  precise  spot,  it 
is  no  longer  seen.  The  conclusion  which  he  drew  from  this  fact 
was,  that  the  seat  of  vision  is  not  the  retina,  but  the  choroid  coat ; 
for  at  this  spot  the  choroid  coat  is  wanting,  being  perforated  to 
admit  of  the  passage  of  the  optic  nerve.  But  the  phenomena  is 
better  accounted  for  by  the  consideration,  that  there  is  present  at 
that  spot  the  central  artery  of  the  retina,  which  here  divides  itself 

*  [The  iris  has  also  a  great  agency  in  correcting  this  aberration  of  refrangi- 
bility, by  preventing  the  rays  of  light  from  falling  near  the  margins  of  the 
crystalline,  and  causing  them  to  innpinge  upon  the  centre,  where  the  opposite 
surfaces  are  nearly  parallel,  and  consequently  the  dispersion  of  the  rays  is 
least.] 

t  Phil.  Trans,  for  1668,  vol.  iii.  No.  35,  p.  668 ;  and  also  Memoires  de 
I'Acad.  i.  68,  and  102. 


PHENOMENA   OP    SENSATION.  287 

into  a  number  of  radiating  branches,  and  excludes  the  presence 
of  nervous  matter,  in  which,  judging  from  the  analogy  of  all  the 
Other  senses,  the  power  of  communicating  sensation  exclusively 
resides.  This  defect  in  vision,  if  we  may  so  term  it,  is  seldom 
perceived  when  both  ej^es  are  used,  because  the  optic  nerve 
enters  each  eye  obliquely,  and  on  different  sides  of  the  centre  of 
the  retina ;  so  that  they  can  never  both  receive  the  image  of  the 
same  object  at  the  same  time. 

675.  The  defects  of  the  eyes  of  some  persons  with  respect  to 
their  refractive  powers  produce  what  is  called  long-sightedness, 
when  these  powers  are  deficient ;  and  short-sightedness,  when  too 
great.  The  source  of  former  imperfection,  which  constitutes  the 
presbyopic  eye,  may  often  be  traced  to  the  effects  of  age,  which 
produces  a  flattening  of  the  cornea  ;  and  probably  also  impairs 
that  voluntary  power  by  which  the  refractions  may  be  increased 
when  near  objects  are  viewed.  The  short-sighted  or  myopic  eye, 
has  generally  an  excessive  convexity  of  the  cornea,  which  may 
be  diminished,  but  is  very  seldom  materially  so,  by  the  progres's 
of  age.  The  remedies  for  these  defects  are  obvious  ;  namely,  the 
use  of  convex  spectacles  for  the  presbyopic,  and  of  concave  spec- 
tacles for  the  myopic  eye  ;  the  former  supplying  the  deficiency 
in  the  power  of  refraction ;  the  latter  correcting  its  excess. 

676.  Such  then  are  the  means  employed  for  producing  certain 
impressions  on  each  retina,  which  it  is  the  office  of  the  optic 
nerves  to  transmit  to  the  sensorium,  where  these  give  rise  to  cor- 
responding sensations.  The  inquiry  into  the  perceptions  arising 
in  the  mind  in  consequence  of  these  sensations  belongs  to  another 
branch  of  the  subject  hereafter  to  be  considered.  It  will  be  suffi- 
cient in  this  place  to  point  out  the  general  fact  relating  to  the 
physiology  of  the  eye,  that  the  impression  made  upon  each  point 
of  the  retina,  produces  in  the  sensorium  a  distinct  impression, 
suggesting  to  the  mind  a  distinct  sensation. 


CHAPTER   XVI. 

PHYSIOLOGICAL     LAWS     OF     SENSATION". 

Sect.  I. — Phenomena  of  Sensation. 

677.  Having  examined  the  different  modes  in  which  impres- 
sions are  made  upon  the  extremities  of  the  nerves  situate  in  the 
respective  organs  of  sense,  we  have  next  to  direct  our  attention 
to  the  physiological  phenomena,  which  ensue  on  those  impres- 
sions being  received. 


288  SENSORIAL    FUNCTIONS. 

1.  Specific  Endowments  of  the  Nerves  of  Sensation. 

678.  The  extremities  of  the  nerves  intended  to  receive  these 
impressions  appear  in  general  to  be  expanded  over  a  certain 
extent  of  surface,  and  to  be  of  a  softer  texture  than  the  nerves 
themselves.  This  difference  appears  to  arise  from  their  being 
divested  of  the  membranous  covering  which  closely  binds  to- 
gether the  filaments  composing  the  nerves,  while  they  are  pursu- 
ing their  course  from  one  part  to  another.  Such  expansions  are 
noticed  in  the  optic,  auditory,  and  olfactory  nerves,  and  probably 
also  in  those  distributed  to  the  papillse  of  the  tongue,  and  the 
cutis.  The  nerve  of  each  particular  sense  appears  to  have  dif- 
ferent specific  endowments.  Thus  the  optic  nerve  and  retina 
are  peculiarly  adapted  to  be  afllected  by  the  impressions  of  light ; 
and  are  not  fitted  to  convey^any  other  impressions.  There  are 
experiments  recorded  which  tend  to  show,  that  irritation  of  these 
nerves  does  not  communicate  pain,  as  is  the  case  with  that  of 
nerves  sent  to  other  parts  of  the  body.  On  the  other  hand,  no 
other  nerve  in  the  body  is  capable  of  exciting,  by  any  change 
that  can  be  induced  upon  it,  the  sensation  of  light,  as  was  pre- 
tended in  the  case  of  the  celebrated  imposture  of  Miss  M'Avoy 
of  Liverpool,  who  endeavoured  to  persuade  people  that  she  could 
see  with  the  tips  of  her  fingers  :  or  in  the  more  elaborate  delu- 
sions of  animal  magnetism,  in  which  persons  are  stated  to  be 
able  to  read  a  piece  of  writing  applied  to  the  pit  of  the  stomach, 
or  nape  of  the  neck,  by  optical  impressions  made  on  different 
parts  of  the  skin. 

679.  That  the  optic  nerves  are  incapable  of  exciting  by  their 
action  any  other  sensations  than  those  of  light,  is  farther  rendered 
probable  by  the  circumstance  that  these  sensations  may  be  pro- 
duced by  other  causes  than  those  which  usually  give  rise  to 
them ;  such  as  impressions  of  a  mechanical  nature.  A  blow  in 
the  eye,  producing  sudden  pressure  on  the  retina,  excites  the 
sensation  of  a  flash  of  light.  The  appearance  of  brilliant  spangles 
in  the  field  of  vision  is  often  the  result  of  too  active  a  state  of 
circulation  in  the  vessels  of  the  retina,  which  excites  in  the  fibres 
of  the  nerves  actions  similar  to  those  produced  by  the  presence 
of  fight.  The  galvanic  influence  affecting  the  same,  or  even 
neighbouring  nerves,  produces,  in  like  manner,  the  sensation  of  a 
flash  of  light.  Analogous  facts  have  been  noticed  with  regard 
to  other  senses.  The  v^'ell-known  sensations  of  singing  in  the 
ears  is  the  consequence  of  an  action  of  the  auditory  nerves, 
excited  by  the  state  of  the  circulation  in  the  organ  of  hearing, 
and  is  probably  totally  unconnected  with  any  real  sonorous  vi- 
brations communicated  to  that  organ. 


MODIFICATIONS   OP    IMPRESSIONS.  289 

2.  Modifications  of  Impressions. 

680.  In  order  that  an  in:ipression  made  upon  the  sentient 
extremity  of  a  nerve  may  excite  sensation,  it  must  be  applied  for 
a  certain  time;  for  if  it  be  of  too  transient  a  duration,  no  effect, 
as  far  as  regards  sensation,  is  produced.  This  is  well  exempli- 
fied in  the  case  of  vision ;  we  lose  sight  of  an  object  in  very 
rapid  motion,  because  the  impression  made  by  its  image  on  the 
different  points  of  the  retina  on  which  it  is  successively  formed, 
is  of  too  transient  a  nature  to  excite  those  actions  which  produce 
sensation. 

681.  On  the  other  hand,  when  a  distinct  impression  has  been 
made  on  the  nerve,  that  impression  has  a  certain  duration,  inde- 
pendently of  the  continuance  of  the  cause  which  excited  it ;  for 
the  sensation  produced  is,  to  a  certain  extent,  permanent.  This 
is  also  shown,  in  the  case  of  vision,  by  several  experiments 
familiar  to  all,  such  as  whirling  rapidly,  with  a  circular  motion, 
an  object  brightly  illuminated,  which  gives  rise,  as  is  well  known, 
to  the  appearance  of  a  continuous  circle  of  light.  Many  optical 
deceptions  are  founded  on  the  same  principle,  such  as  that  of  the 
Tliaumatrope,  of  the  Phantascope,  or  Phenikisticope,  and  the 
curved  appearance  of  the  spokes  of  a  revolving  wheel  when 
viewed  through  parallel  bars,  of  which  last  phenomena  the  theory 
has  been  elsewhere  given  by  the  writer  of  this  treatise  ;*  and  also 
the  appearance  of  a  similar  kind  noticed  by  Mr.  Faraday .f 

682.  One  of  the  consequences  of  the  law  of  the  permanence 
of  sensations  is,  that  impressions,  which  rapidly  succeed  one 
another  in  the  same  nerve,  are  not  distinguishable  as  separate 
impressions,  but  produce  a  blending  together,  or  coalescence  into 
one  sensation.  Thus,  if  a  circle  painted  in  different  parts  of  the 
circumference  with  different  colours,  be  rapidly  whirled  round 
its  centre,  the  colours  are  blended  together  into  one  tint ;  and  if 
the  different  prismatic  colours  of  the  spectrum  be  properly  adjusted 
as  to  their  relative  proportions,  the  effect  of  this  coalescence  of 
the  sensations  excited  by  the  whole  is  that  of  a  white  colour. 
The  thaumatrope  may  also  be  made  to  illustrate  this  principle ; 
for  the  pictures  on  the  two  sides  of  the  card  appear,  by  the  rapid 
revolution  of  the  card,  to  coalesce  into  one. 

683.  The  most  remarkable  and  complete  illustration  of  the 
same  principle  is  afforded  by  musical  sounds,  which  though  they 
appear  continuous,  are,  in  fact,  composed  of  separate  impulses, 
repeated  at  very  short,  but  regular  intervals  of  time. 

684.  Another  law  of  sensation,  is,  that  when  a  nerve  has  re- 
ceived a  strong  impression,  that  nerve  is  proportionally  weakened 

*  Philosophical  Transactions  for  1815. 

f  Journal  of  the  Royal  Institution,  vol.  i.  p.  205.  See  also  Dr.  Roget's 
Bridgewater  Treatise,  vol.  ii.  p.  524.  [Amer.  edit.  ii.  368.] 

25 


290  SENSORIAL    FUNCTIONS. 

for  a  certain  time  after,  and  is  less  susceptible  of  a  similar  impres- 
sion from  the  application  of  the  same  cause.  The  eye,  after 
being  dazzled  by  a  strong  light,  has  its  sensibility  diminished  to 
the  impressions  of  a  weaker  light.  Different  parts  of  the  retina 
thus  acquire  different  degrees  of  susceptibility  of  being  affected 
by  the  same  quantities  of  light.  Thus,  if  the  eyes  be  directed 
steadily  to  a  bright  object  for  a  certain  length  of  time,  and  be 
then  transferred  to  a  white  sheet  of  paper,  a  dark  spot,  having 
the  figure  of  that  object,  will  be  seen  on  the  paper,  in  consequence 
of  that  portion  of  the  retina,  on  which  the  luminous  image  had 
been  impressed,  being  fatigued,  and  rendered  less  excitable  than 
those  parts  of  the  retina  which  did  not  receive  that  image.  The 
light  from  the  paper  which  arrives  at  that  part  of  the  retina, 
which  had  received  the  impressions  of  the  bright  object,  will 
produce  less  effect  on  that  part,  than  the  light  of  equal  intensity 
from  other  parts  of  the  paper  does  on  the  other  parts  of  the 
retina.  Those  parts^of  the  paper,  which  are  situate  so  as  to 
have  their  image  on  the  exhausted  part  of  the  retina,  appear 
darker,  therefore,  than  the  rest;  and  hence  arises  the  appearance 
of  a  dark  image.  The  experiment  may  be  reversed  by  fixing 
the  eyes  attentively  for  some  time  on  a  dark  object  on  a  white 
ground,  and  then  transferring  it  to  some  other  part  of  the  white 
ground  ;  when  imrnqdiately  a  brighter  spot,  corresponding  in  size 
and  figure  to  the  dark  object,  will  be  seen. 

685.  These  appearances,  which  imitate  those  of  real  objects, 
have  been  called  ocular  spectra.  The  susceptibility  of  the  retina 
to  receive  impressions  of  particular  colours  is  also  found  to  be 
affected  in  the  same  manner,  when  any  one  of  them  has  been 
strongly  impressed.  Thus  the  spectrum  of  a  coloured  object, 
while  it  has  the  same  dimensions  and  figures  as  the  object,  will 
at  the  same  time  have  an  opposite  colour,  when  the  eye  is  trans- 
ferred to  a  white  ground.  It  will  have  what  is  called  the  com- 
•plernentary  colour  to  that  of  the  object  itself;  that  is,  it  will  have 
that  tint  which  results  from  the  admixture  of  all  the  colours 
composing  white  light,  \yhen  the  latter  colour  is  left  out.  Thus 
red  and  green,  yellow  and  purple,  blue  and  orange,  being  com- 
plementary colours  respectively  to  each  other,  the  ocular  spec- 
trum of  a  red  object  will  be  green,  that  of  a  green  object  red, 
and  so  with  all  the  others.*       ■' 

686.  We  may  here  observe,  that  the  appearances  of  spectra, 
above  described,  are  merely  temporary ;  for  the  several  parts  of 
the  retina  soon  regain  their  natural  state  of  equable  sensibility. 

687.  Illustrations  of  this  law  readily  present  themselves  when 
we  search  for  its  application  with  regard  to  all  the  other  senses. 

*  For  more  ample  details  on  this  subject,  the  reader  may  be  referred  to  an 
Essay  on  Ocular  Spectra,  By  Dr.  Charles  Darwin,  published  in  the  76th^ 
volume  of  the  Philosophical  Transactions,  and  reprinted  in  Dr.  Darwin's 
Zoonomia. 


'   CONDITIONS    NECESSARY    FOR    SENSATION.  291 

Sounds  which  are  too  loud  produce  temporary  deafness,  or  at 
least  impair  for  a  time  the  scnsibihty  of  the  ear  to  weaker  sounds. 
Similar  phenomena  are  observed  as  to  odours  and  tastes,  with 
reference  to  their  appropriate  senses.  The  sensibiHty  of  the  skin 
to  different  temperatures  varies  considerably  according  to  the 
previous  impressions  which  have  been  made  upon  it.  Thus  the 
same  body  may  appear  either  hot  or  cold,  according  to  the  pre- 
vious temperature  of  the  hand  which  is  applied  to  it. 


Sect.  II. — Conditions  necessary  for  Sensation. 

688.  The  sensibility  of  the  sentient  extremities  of  nerves  or 
their  capabilit}/  of  receiving  such  impressions  as  lead  to  their  appro- 
priate sensations,  is  dependent  on  certain  conditions  of  the  organ. 
These  conditions  are  principally  the  folUowing.  First,  it  is 
necessary  that  the  organ  receive  a  proper  supply  of  arterial 
blood  by  the  vessels  circulating  through  it,  and  particularly  through 
that  part  on  which  the  nerves  are  distributed.  Secondly,  it  is 
required  that  the  expansion  of  the  nerve  belonging  to  the  organ 
should  be  exempt  from  excessive  pressure.  Compression  of  a 
nerve  in  any  part  of  its  course  immediately  puts  a  stop  to  all  its 
functions;  and  consequently  its  power  of  receiving  and  convey- 
ing impressions  is  suspended  as  long  as  the  pressure  is  continued. 
On  the  removal  of  the  pressure,  provided  it  has  not  been  too  violent, 
or  too  long  continued,  the  nerve  after  a  certain  time,  generall)^ 
recovers  its  powers.  Thirdly,  a  certain  temperature  is  requisite 
for  the  maintenance  of  sensibility  in  the  nerves.  The  benumbing 
effect  of  cold  is  well  known,  and  extends  generally  to  all  the  func- 
tions of  the  nervous  system.  It  is  very  probable,  that  this  operation 
of  cold  is  referable  to  its  retarding  or  arresting  the  circulation  in 
the  capillary  vessels  ;  and  it  might,  therefore,  perhaps,  be  included 
in  the  causes  which  influence  the  first  of  the  conditions  here 
enumerated.  Lastly,  the  office  of  every  nerve  being  to  transmit 
impressions  from  one  of  their  extremities  to  the  other,  it  is  neces- 
sary for  the  due  performance  of  this  function,  that  an  uninterrupted 
continuity  of  their  filaments  should  be  preserved  throughout  their 
whole  course.  The  complete  division  of  a  nerve  in  any  part, 
necessarily  prevents  this  transmission,  and  destroys  the  function 
of  the  nerve. 

689.  Irritations  applied  to  the  nerve  in  any  part  of  its  course^ 
produce  sensation,  provided  the  communication  of  that  part  with 
the  brain  be  uninterrupted  by  any  of  the  causes  above  specified. 
Thus,  if  a  nerve  be  tied  or  divided  at  any  point,  irritations  applied 
below  the  ligature  or  division  will  produce  no  effect  as  to  sensa- 
tion ;  but  when  applied  above  that  point,  sensation  immediately 
follows.    What  is  here  said  applies  more  particularly  to  the  nerves 


292  SENSORIAL    FUNCTIONS. 

distrbuted  to  various  parts  of  the  body,  and  especially  to  the 
integuments ;  the  irritation  of  which  nerves  gives  rise  to  a  sense 
of  pain.  The  nerves  of  the  senses  of' sight,  of  hearing,  of  smell, 
and  of  taste,  are  so  situate  as  hardly  to  admit  of  being  the  subjects 
of  experiments  which  might  decide  the  question  as  to  what  kinds 
of  sensation  would  be  excited  by  irritations  directly  applied  to 
them :  and  whether  these  sensations  would  be  similar  to  those 
they  usually  convey  from  impressions  made  upon  their  extremities. 
Analogy  would  undoubtedly  be  in  favour  of  such  similarity. 
Persons  who  have  lost  a  limb  by  amputation,  experience  sensations 
not  only  of  pain,  but  also  of  touch,  and  of  muscular  motion,  exactly 
similar  to  those  which  they  formerly  derived  from  the  parts  of  the 
limb  which  they  have  lost.  These  sensations  arise  from  imitations 
taking  place,  either  in  the  lower  extremities  of  the  nerves  which 
have  been  divided,  and  which  remain  in  the  stump,  or  in  the  brain 
itself. 

690.  The  most  remarkable  circumstance  attending  the  commu- 
nication of  irritations  along  the  nerves  of  sensation,  is  the  celerity 
of  the  transmission.  It  appears,  indeed,  to  be  instantaneous,  and 
can  be  compared  only  to  the  rapidity  of  the  electric  fluid  passing 
along  a  conducting  body. 


Sect.  III. —  Theories  of  Sensation. 

691.  We  are  completely  ignorant  of  the  nature  of  that  powder 
by  which  the  nerves  effect  this  rapid  communication  along  the 
lines  of  their  fibres,  and  even  of  the  changes  which  take  place  in 
the  nerve  while  it  is  performing  this  function.  Several  hypotheses 
have  been  proposed  with  a  view  to  supply  this  chasm  in  our 
knowledge.  The  oldest  of  these,  and  that^which  maintained  its 
ground  for  many  centuries,  is,  that  the  brain  and  nerves  are 
furnished  with  a  certain  fluid,  which  was  called  the  animal  spirits, 
and  was  the  medium  of  communication  between  the  different 
parts  of  the  nervous  system.  Traces  of  this  theory  may  be  found 
in  the  writings  of  Hippocrates ;  but  it  derived  its  principal  support 
from  Descartes,  who  reduced  it  to  a  regular  form,  and  powerfully 
recommended  it  by  the  force  of  his  authority.  According  to  the 
views  of  those  who  espouse  this  theory,  the  brain  is  considered 
as  an  organ  whose  principal  office  it  is  to  secrete  the  animal 
spirits,  which  are  of  a  very  subtile  and  ethereal  nature,  and  to 
supply  them  to  the  nerves,  which  were  considered  to  be  the  natural 
excretory  ducts  of  the  brain.  The  existence  of  this  fluid  was,  for 
a  very  long  period,  universally  admitted  by  physiologists,  and  the 
doctrines  founded  upon  it  were  more  or  less  mixed  up  with  all  the 
reasonings  of  physicians  respecting  the  causes  and  phenomena  of 
diseases,  and  the  effects  of  remedies.     Traces  of  the  influence  of 


THEORIES    OP    SENSATION.  293 

this  doctrine  may  be  found  in  the  popular  language  of  medicine 
even  in  the  present  day,  when  the  hypothesis  from  which  it  is 
derived  is  deservedly  exploded  as  perfectly  gratuitous,  and  devoid 
of  any  just  foundation. 

692.  Another  hypothesis  invented  to  account  for  the  propaga- 
tion of  impressions  along  the  fibres  of  nerves,  was  that  of  their 
depending  on  vibrations  or  periodical  oscillations  of  their  parti- 
cles, analogous  to  those  of  the  strings  of  a  harpsichord  when 
producing  musical  notes.  The  great  champion  of  this  doctrine 
was  Hartley,*  who  embellished  it  by  his  beautiful  applications  to 
a  great  variety  of  phenomena  relating  to  sensations,  and  even  to 
the  intellectual  operations.  It  afforded  a  happy  explanation  of 
many  of  the  phenomena  of  ocular  spectra,  and  of  those  depend- 
ing on  the  permanence  of  sensations.  It  is  needless  to  remark, 
that  this  hypothesis  is  equally  visionary  and  destitute  of  any  solid 
basis  as  the  former. 

693.  All  these  mechanical  theories  are  overturned  by  the  fact 
that  no  tubular  structure  can  be  discovered,  on  the  minutest  ana- 
tomical scrutiny,  to  exist  in  the  filaments  which  compose  the 
nerves  ;f  nor  can  the  slightest  motion  be  detected  in  any  of  their 
parts,  while  they  are  actively  transmitting  the  impressions  of 
sensation. 

694.  The  latest  hypothesis  as  to  the  nature  of  nervous  power 
is,  that  it  is  identical  with  electricity.  It  is  supported  principally 
by  the  experiments  we  have  already  mentioned,  in  which,  after 
the  par  vagum  was  divided,  so  as  entirely  to  intercept  its  action 
in  promoting  the  secretion  of  the  gastric  fluid,  secretion  was  re- 
stored by  transmitting  the  galvanic  fluid  along  the  lower  portion 
of  the  nerve.  The  experiment,  indeed,  applies  only  to  a  parti- 
cular office  of  the  nervous  power,  namely,  that  of  promoting 
secretion ;  but  the  hypethesis  it  suggested  has  been  extended  to 
all  the  other  functions  of  the  nerves,  and  of  course  to  their  power 
of  transmitting  thbse  impressions  which  give  rise  to  sensation. 

*  On  Man.  A  full  account  of  Hartley's  theory  is  given  by  Dr.  Priestley, 
in  a  separate  work  bearing  that  title. 

f  [We  have  already  shown,  (note  to  §588,)  that  some  distinguished  ob- 
servers of  the  present  day  still  maintain,  that  the  neryes  are  tubular.] 


25» 


294  SENSORIAL    FUNCTIONS. 

CHAPTER    XVII. 

FUNCTIONS   OF    THE    SENSORIUM.  ^ 

Sect.  L — Locality  of  the  Sensorium. 

695.  If  we  except  the  nerves  appropriated  to  the  organs  of  the 
specia]  senses  of  sight,  hearing,  smell,  and  taste,  and  those  dis- 
tributed on  the  face,  and  other  neighbouring  parts,  all  the  nerves 
subservient  to  sensation  appear  to  terminate  in  the  spinal  cord. 
We  are  then,  in  the  first  place,  to  determine  whether  the  impres- 
sions which  these  nerves  convey  to  that  organ,  are  transmitted 
to  any  other  part  of  the  nervous  system,  previously  to  sensation 
being  produced. 

696.  Experiments  in  all  the  animals  whose  structure,  as  far  as 
regards  this  part  of  the  nervous  system,  is  analogous  to  the  human, 
have  established  the  general  fact,  that  sensation  does  not  take 
place,  unless  the  part  of  the  spinal  cord  to  which  the  nerve  is 
connected,  communicates  by  an  uninterrupted  continuity  of  sub- 
stance with  the  brain.  The  division  of  the  spinal  cord  near  the 
foramen  magnum,  instantly  renders  the  whole  body  insensible ; 
but  it  does  not  appear  so  immediately  to  deprive  the  parts  about 
the  face  of  sensibilitj^  for  some  degree  of  it  appears  to  be  retained 
as  long  as  the  circulation  continues.  The  injury,  indeed,  soon 
becomes  fatal,  by  the  circulation  ceasing  in  consequence  of  the 
interruption  to  the  function  of  respiration.  The  effects  of  injuries 
to  the  spinal  cord  occurring  to  men  from  accidents  of  various 
kinds,  afford  ample  confirmation  of  the  fact  that  the  brain  is  the 
general  centre  to  which  all  impressions  -made  upon  the  nerves 
must  ultimately  be  brought  before  they  can  excite  sensation. 

697.  Admitting  the  brain  to  be  the  immediate  organ  of  sensa- 
tion, it  next  becomes  a  question,  whether  any  particular  part  of 
the  brain  is  more  especially  appropriated  to  the  exercise  of  this 
function.  It  is  to  such  a  part,  supposing  it  to  exist,  that  the  name 
of  sensorium  has  been  applied.  There  are  two  modes  of  con- 
ducting this  inquiry  ;  the  first  is  by  tracing,  very  carefully,  the 
filaments  of  all  the  nerves  which  are  immediately  connected  with 
the  brain,  and  endeavouring  to  discover  if  they  unite  in  any 
central  part  of  that  organ,  which  may  accordingly  be  supposed 
to  be  the  seat  of  sensation ;  or,  in  other  words,  the  sensorium. 
The  second  mode  of  investigating  the  subject,  is  to  ascertain  if 
any  one  part  of  the  brain  can  be  discovered,  on  which  impressions 
directly  made,  are  invariably  productive  of  sensation. 


'  REQUISITE    CONDITIONS    OF    THE    SENSORIUM.  295 

698.  The  fibrous  substance  of  the  spinal  cord,  being  directly 
continuous  with  the  medulla  oblongata,  nfiay  be  supposed  to  ter- 
minate in  that  part  of  the  brain  ;  so  that,  viewing  the  spinal  cord 
as  a  collection  of  all  the  fibres  of  the  nerves  of  sensation  continued 
along  its  whole  length,  these  nerves  themselves  may  be  considered 
as  following  this  course,  and  having  this  termination.  These 
fibres  are  found  more  particularly  to  converge  towards  the  cor- 
pora quadrigemina,  and  crura  cerebri.  Now,  it  happens  that 
this  is  also  the  very  spot  with  which  the  nerves  of  the  senses, 
whose  organs  are  in  the  head,  namely,  the  fifth,  seventh,  and 
eighth  pairs,  are  more  particularly  connected.  It  appears,  also, 
from  the  late  investigations  of  the  French  physiologists,  that  no 
part  of  the  brain  higher  than  the  corpora  quadrigemina,  and  no 
part  whatever  of  the  cerebellum,  is  essentially  concerned  in  sen- 
sation ;  for  it  is  found  that  in  animals  the  power  of  sensation 
remains,  even  after  the  removal  of  all  the  parts  of  the  brain,  or 
of  the  cerebellum,  higher  than  this  spot.  The  conclusion  which 
has  been  deduced  from  these  experiments  is,  that  the  medulla 
oblongata,  and  more  particularly  that  segment  of  it  to  which  the 
nerves  of  the  head  are  united,  is  the  organ  most  essentially  con- 
nected with  the  mental  change  constituting  sensation.  But  it  is 
not  probable  that  these  corporeal  changes  immediately  connected 
with  sensation,  are  confined  to  a  single  point  in  the  brain,  which 
might  emphatically  be  termed  the  seat  of  the  soul,  as  Descartes 
expressed  it,  when  he  boldly  pronounced  the  pineal  gland  to  be 
that  spot.* 


Sem:!T.  II. — Requisite  Conditions  of  the  Sensorium. 

699.  A  multitude  of  facts  tend  to  confirm  the  view  of  the  sub- 
ject which  has  here  been  taken.  The  same  conditions  as  those 
which  are  required  for  the  exercise  of  the  functions  of  the  nerves 
in  every  part  of  their  course,  are  equally  necessary  for  the  per- 
formance of  those  of  the  brain.  It  is  indispensable  that  the 
circulation  in  the  brain  should  be  in  a  healthy  state,  and  that 
arterial  blood  be  supplied  by  its  vessels.  It  is  indispensable  that 
a  proper  temperature  be  preserved ;  and  it  is  likewise  indispen- 
sable that  the  brain  be  not  compressed  by  any  considerable  force. 
A  failure  in  any  one  of  these  conditions,  produces  total  depriva- 
tion of  the  power  of  sensation,  as  well  as  of  all  the  other 
functions  of  the  brain.  This  effect  is  found  to  result  more 
particularly  when  pressure  is  made  in  the  direction  of  the 
medulla  oblongata  ;  for  in  that  case  complete  insensibility  takes 
place;  and  on  the  removal  of  the  pressure,  the  faculty  of  sensa- 

*  [Dunglison's  Physiology,  3d  edit.  i.  308.] 


296  SENSORIAL    FUNCTIONS. 

tion  slowly  returns;  but  if  any  considerable  injury  has  been 
inflicted  on  that  part,  the  power  of  sensation  is  irrecoverably 
lost. 

700.  It  is  probable  that  most  of  the  laws  which  regulate  the 
functions  of  the  nerves  with  respect  to  sensation,  apply  with 
equal  truth  to  the  sensoriurn  itself;  but  with  regard  to  several  of 
the  phenomena,  it  is  difficult  to  determine  whether  they  depend 
on  affections  of  the  sensoriurn,  or  of  the  extremities  of  the  nerves, 
situate  in  the  organ  of  sense.  We  must  despair  of  being  able 
to  resolve  this  question,  because  the  change  which  takes  place  in 
both  these  parts,  appear  to  be  simultaneous.  The  impaired  power, 
for  example,  which  is  the  result  of  a  strong  impression  from  an 
object  of  sense,  may  arise  equally  from  the  exhaustion  of  that 
part  of  the  sensoriurn  to  which  the  impression  is  communicated, 
as  of  that  of  the  sentient  extremity  of  the  nerve  ;  and  we  hkve  no 
means  of  discriminating  between  them. 

701.  Another  point  of  resemblance  is,  that  irritations  applied 
to  the  sensorium,  from  other  sources  than  the  nerves  themselves, 
give  rise  to  the  same  train  of  sensations  as  impressions  commu- 
nicated through  the  nerves.  These  irritations  may  be  given  by  the 
pressure  of  blood  circulating  in  the  arteries  of  the  sensorium  ; 
and  this  is  probably  the  source  of  many  of  those  sensations  gene- 
rally ascribed  to  affections  of  the  nerves,  or  of  the  organs  of 
sense.  Pains,  and  other  sensations  in  various  parts  of  the  body, 
arise  from  affections  of  the  brain.  The  same  origin  may  often 
be  assigned  to  sensations  which  arise  in  dreams,  and  likewise  to 
various  spectral  illusions  which  affect  persons  who  are  awake, 
and  aware  of  their  being  deceptions  of  the  sense.  In  delirium 
and  insanity,  the  sensations  from  this  cause  assume  a  fearful  de- 
gree of  intensity,  and  are  accompanied  by  a  fixed  belief  in  their 
reality. 


Sect.  III. — Laws  of  Recurrence,  and  of  the  Association  of 
Impressions. 

702.  With  regard  to  all  the  subsequent  changes  and  operations 
which  take  place  when  sensation  has  been  excited,  it  is  extremely 
difficult  to  pronounce  how  much  of  the  phenomena  are  purely 
mental,  and  how  much  are  strictly  the  result  of  corporeal  changes 
connected  and  associated  together  by  physical  laws.  In  other 
words,  it  is  difficult  to  determine  what  are  the  operations  in 
which  the  mind  is  purely  passive,  and  dependent  on  the  actions 
of  its  bodily  organs,  and  what  are  those  in  which  it  exerts  a 
spontaneous  power  of  action,  and  thereby  reacts  upon  those 
organs,  and  produces  in  them  a  series  of  changes  which  lead  to 
the  most  important  results.     The  distinction  we  are  attempting 


ASSOCIATION    OF    IMPRESSIONS.  297 

to  draw,  is  founded  upon  this  essential  difference  in  the  order  of 
sequence  of  the  phenomena,  that  in  the  one  the  organic  change 
precedes  the  mental  change,  and  in  the  other  succeeds  to  it. 

703.  The  two  principal  physiological  laws  relating  to  the  former 
of  these  physical  changes,  namely,  those  which  precede  the  mental 
affections,  are,  first,  the  law  of  spontaneous  recurrence.  When- 
ever an  impression  of  a  certain  intensity  has  been  made  upon  the 
organs  of  sense,  the  sensation  which  is  produced  by  it,  after  dis- 
appearing for  a  certain  time,  recurs  without  the  presence  of  the 
cause  which  originally  excited  it ;  and  this  happens  repeatedly, 
and  without  any  corresponding  effort  of  the  mind,  and  often  in 
opposition  to  any  effort  which  can  be  made  to  counteract  the 
tendency.  This  spontaneous  recurrence  of  sensations  is  proba- 
bly the  result  of  the  repetition  of  those  changes  in  the  sensorium 
which  originally  gave  rise  to  them.  In  the  language  of  meta- 
physics, the  corresponding  mental  nffections  are  termed  ideas, 
in  order  to  distinguish  them  from  the  similar  and  more  vivid 
affection  excited  by  the  primitive  impression,  and  to  which  the 
term  sensation  is  more  particularly  appropriated. 

704.  The  second  law  which  regulates  the  unknown  affections 
of  the  brain  connected  with  the  passive  phenomena  of  mind,  is 
that  oi  association,  or  the  law  by  which  impressions,  and  conse- 
quently the  corresponding  ideas,  recur  in  the  same  order  of 
sequence  as  that  in  which  they  were  originally  excited.  The 
phenomena  of  disease,  and  the  operation  of  different  agents  wdiich 
modify  the  state  of  circulation  in  the  brain,  and  the  conditions  of 
the  nervous  powers,  afford  ample  evidence  that  the  modes  of  as- 
sociation, and  of  the  sequence  of  impressions  and  ideas,  are  de- 
pendent on  the  physical  condition  of  the  brain,  and  result  from 
certain  changes  taking  place  in  that  organ. 

705.  The  views  here  presented,  far  from  being  favourable  to 
the  doctrine  of  materialism,  are  directly  opposed  to  it ;  since  they 
necessarily  imply  the  existence  of  an  essential  distinction  be- 
tween mind  and  matter,  and  aim  only  at  tracing  the  connexions 
which  have  been  estabhshed  between  them  by  the  divine  Author 
of  our  existence. 

706.  Such,  then,  being  the  physiological  connexions  which 
exist  betv^'een  the  physical  changes  taking  place  in  the  brain,  and 
the  passive  phenomena  of  the  mind,  it  is  not  an  unreasonable 
supposition,  that  the  voluminous  mass  of  cerebral  substance 
which,  in  the  human  brain  especially,  has  been  superadded  to 
the  medulla  oblongata,  or  to  the  immediate  physical  seat  of  sen- 
sation, is  in  some  way  subservient  to  that  astonishing  range  of 
intellect  and  combination  of  mental  faculties  which  are  found  in 
man.  We  may  conjecture  also,  with  much  appearance  of  pro- 
bability, that  in  the  lower  animals,  the  intellectual  endowments 
which  mark  several  of  the  more  intelligent  races  are  connected 
with  similar,  though  inferior,  expansions  of  cerebral  substance. 


298  SENSORIAL    FUNCTIONS. 

707.  All  the  mental  phenomena  in  which  the  mind  is  passive 
have  been  referred  by  metaphysicians  to  the  principle  of  associ- 
ation, and  consequently  may,  in  as  far  as  this  principle  is  con- 
cerned, be  connected  with  the  physical  changes  above  noticed. 
Hence  we  find  the  memory,  which  is  the  direct  result  of  that 
law,  is  more  especially  liable  to  be  impaired  by  certain  physical 
states  of  the  brain,  such  as  those  induced  by  severe  concussion, 
by  fevers,  and  by  the  progress  of  age. 

708.  As  scarcely  any  thing  is  known  with  regard  to  the  phy- 
sical changes  which  take  place  in  the  brain  in  the  relations  which 
they  bear  to  mental  phenomena,  the  further  consideration  of 
these  phenomena  belongs  properly  to  psychology  rather  than  to 
the  subject  of  this  treatise.  The  inquiry  must  here  be  taken  up 
by  the  metaphysician,  whose  province  it  becomes  not  the  physio- 
logist to  invade. 


Sect.  IV. —  Volition  and  Voluntary  Motion. 

709.  Leaving,  therefore,  to  the  metaphysician  the  analysis  of 
those  mental  phenomena,  which,  however  dependent  they  may 
be  for  their  existence  on  the  healthy  actions  of  the  brain,  require 
modes  of  investigation  different  from  those  of  physiology,  and 
lead  to  results  very  remote  from  any  conceivable  laws  of  mate- 
rial agency ;  we  may  resume  the  subject  at  the  point  when,  in 
consequence  of  the  mental  acts  of  volition,  by  which  term  we 
here  mean  to  express  the  endeavour  to  produce  certain  specific 
movements  of  the  body,  new  changes  are  again  produced  in  the 
cerebral  organs,  and  new  trains  of  physical  phenomena  succeed. 
That  this  mental  effort  of  volition  constitutes  a  distinct  step  in 
the  series  of  phenomena,  is  proved  by  the  instances  of  paralysis, 
in  which  the  patient  is  conscious  of  making  the  effort  to  move 
the  palsied  limb,  yet  no  motion,  or  even  sensation  of  motion, 
ensues.  Another  illustration  of  the  same  distinction  is  derivable 
from  a  different  disease  affecting  the  limbs,  namely,  anesthesia, 
which  consists  of  the  loss  of  sensation  only,  while  the  power  of 
voluntary  motion  remains ;  and  in  which  the  voluntary  act  so 
exerted  produces  the  intended  muscular  contractions,  unattended, 
however,  with  the  feelings  which  usually  accompany  them.  The 
same  complete  ignorance  in  which  we  are  with  regard  to  the 
changes  which  take  place  in  sensation,  pervades  our  notions  of 
those  which  attend  vohtion,  in  as  far  as  they  occur  in  the  brain. 
A  few  facts,  indeed,  have  been  collected  with  regard  to  those 
parts  of  the  brain  which  are  impressed,  if  such  a  term  may  be 
used,  antecedently  to  the  voluntary  motions  of  the  limbs.  They 
appear  to  be  chiefly  the  crura  of  the  cerebellum,  and  the  adjacent 
parts  of  the  medulla  oblongata. 


VOLITION    AND    VOLUNTARY    MOTION.  299 

710.  All  the  physical  conditions  which  are  necessary  in  order 
that  sensations  may  be  felt,  are  equally  necessary  for  rendering 
the  cerebral  organs  capable  of  receiving  from  the  mind  those 
impressions  which  lead  to  voluntary  motion.  The  mental  stimulus 
of  volition  produces  a  certain  effect  on  the  origin  of  the  nerves, 
leading  to  the  muscles  employed  in  these  motions,  which  impres- 
sion, being  propagated  along  the  course  of  those  nerves,  excites 
these  muscles  to  contraction.  The  transmission  of  those  impres- 
sions is  made  with  the  same  celerity,  and  probably  by  the  same 
agency,  as  those  which  produce  sensation  ;  but  they  are  made  in 
the  contrary  direction,  namely,  from  the  brain,  instead  oitoicards 
it.  The  same  condition  of  perfect  continuity  of  fibres,  of  freedom 
from  pressure,  and  of  healthy  circulation,  are  essential  requisites 
in  both  cases;  and  every  thing  that  has  been  said  with  regard  to 
the  former,  is  also  appHcable  to  the  latter.  Mechanical  irrita- 
tions, applied  either  at  those  parts  of  the  brain  v/hich  adjoin  the 
origin  of  the  nerves,  or  to  the  nerves  themselves,  either  at  their 
origin,  or  in  any  part  of  their  course,  whether  that  portion  of  the 
nerve  situate  between  the  point  to  which  the  irritation  is  applied 
be  entire  or  divided,  or  compressed  by  a  ligature,  are  found  to 
produce  the  same  muscular  contractions  as  those  which  are  the 
result  of  volition. 

711.  Mr.  Mayo*  ascertained,  that  after  any  nerve  which  sup- 
pHes  a  voluntary  muscle  is  cut  through,  either  in  a  living  animal, 
or  immediately  after  death,  mechanical  irritation  of  the  part  of 
the  nerve  disconnected  with  the  brain,  as  for  instance  the  pinch- 
ing it  with  a  forceps,  causes  a  single  sudden  action  of  the  muscle 
or  muscles  it  supplies.  On  the  other  hand,  a  like  effect  cannot 
be  produced  by  irritating  mechanically  the  nerves  distributed  to 
those  muscles  over  v^'hich  the  will  has  indisputably  no  influence. 
"It  must  be  admitted,  however,"  he  remarks,  "that  this  phenome- 
non is  not  exclusively  confined  to  those  muscles  which  are  allowed 
on  all  hands  to  be  voluntary ;  nor,  indeed,  is  it  shown  in  all  the 
muscles  which  seem  at  first  sight  to  be  directly  under  the  control 
of  the  will."  But  it  is  not  easy,  in  various  instances,  to  determine 
whether  muscular  actions  are  voluntary  or  not;  while  the  point 
of  distinction  proposed  by  Mr.  Mayo  has  the  recommendation  of 
being  easily  verifiable.  Setting  aside,  therefore,  in  the  first  instance, 
the  question  of  the  influence  of  the  will,  let  us  be  satisfied  with 
observing  what  muscles  act  when  a  divided  nerve  that  enters  their 
substance  is  mechanically  irritated," and  what  do  not.  We  may 
afterwards  trace  the  collateral  differences  of  the  two  classes  of 
muscles  which  are  thus  distinguished. 

712.  The  parts  which  are  susceptible  of  this  mode  of  excitement, 
are  the  muscles  of  the  trunk,  head,  and  limbs,  of  the  tongue,  of 
the  soft  palate,  of  the  larynx,  of  the  pharynx,  and  oesophagus,  and 

*  Outlines  of  Human  Physiology,  3d  edit.  p.  39  to  42. 


300  SENSORIAL    FUNCTIONS. 

of  the  lower  outlet  of  the  pelvis.  The  opposite  class  comprehends 
the  heart,  the  stomach,  the  small  and  great  intestines,  and  the 
bladder. 

713.  The  collateral  differences  which  characterize  either  class 
are,  with  exceptions  afterwards  to  be  adverted  to,  the  following : — 

Of  the  muscles  which  act  when  a  nerve  distributed  through 
them  is  mechanically  irritated,  it  may  be  remarked ;  1.  That 
they  admit  of  being  thrown  into  action  by  an  effort  of  the  will. 
2.  That  with  sufficient  attention  and  resolution,  their  action  may 
be  refrained  from.  3.  That  their  action  is  attended  with  a  con- 
scious effort,  and  is  guided  by  sensation.  4.  That  if  divided, 
the  separate  parts  retract  instantaneously  to  a  certain  distance, 
and  subsequently  undergo  no  farther  permanent  shortening. 
5.  That  when  mechanically  irritated,  a  single  and  momentary 
action  of  their  fibres  alone  ensues.  6.  That  they  remain  relaxed, 
unless  excited  by  special  impressions,  both  in  the  living  body,  and 
before  the  loss  of  irritability  after  death.  7.  That  their  action  in 
the  living  body  habitually  results  from  an  influence  transmitted 
from  the  brain  or  spinal  cord  through  the  nerves. 

714.  The  exceptions  to  be  made  against  this  statement,  if  ap- 
plied generally,  are,  that  the  three  first  affections  are  not  easily 
brought  home  to  the  muscular  fibres  of  the  oesophagus,  or  of  the 
lower  part  of  the  pharynx ;  but  it  deserves  at  the  same  time  to 
be  considered,  that  the  lower  part  of  the  pharynx  and  the  cbso- 
phagus  are  in  the  peculiar  situation  of  parts  employed  on  one 
object  alone,  instinctively  and  habitually,  on  the  recurrence  of 
one  impression  ;  a  condition  which  would  soon  reduce  a  strictly 
voluntary  muscle  to  a  state  apparently  removed  from  the  control 
of  the  will. 

715.  Muscles  of  the  preceding  class,  if  we  except  the  fasciculi 
belonging  to  the  pharynx,  and  oesophagus,  and  urethra,  are  so 
disposed  as  to  extend  from  one  piece  to  another  of  the  solid 
frame-work  of  the  body ;  they  enlarge  or  straighten  the  cavities 
of  the  trunk ;  they  produce  the  phenomena  of  the  voice ;  they 
close  the  excretory  passages ;  the  greater  number  are  employed 
to  move  the  limbs  on  the  trunk  and  the  frame  on  the  ground. 
Muscles  of  the  second  class  are  used,  like  the  exceptions  in  the 
preceding,  as  tunics  to  the  hollow  viscera,  the  cavities  of  which 
they  diminish  in  their  action,  and  thus  serve  to  give  motion  to 
their  contents.  The  oesophagus,  indeed,  appears  to  partake  of 
the  nature  of  both  classes  oi"  muscles;  when  the  nervi  vagi  are 
pinched,  one  sudden  action  ensues  in  its  fibres,  and  presently 
after  a  second  of  a  slower  character  may  be  observed  to  take 
place. 

716.  Of  the  muscles  which  do  not  act  on  the  mechanical  irri- 
tation of  any  nerve  distributed  through  them,  it  may  be  remarked, 
1.  That  the  will  cannot  instantaneously  or  directly  produce  action 


VOLITION    AND    VOLUNTARY    MOTION.  301 

in  them.  2.  That  the  resolution  to  abstain  from  their  action  is 
insufficient  to  repress  it.  3.  That  their  action  is  not  attended 
with  a  conscious  eflbrt,  and  seldom  has  reference  to  sensation. 
4.  That  if  divided,  the  retraction  which  follows  is  in  most  in- 
stances slow  and  gradual.  5.  That  if  they  are  mechanically 
irritated,  not  one,  but  a  series  of  actions  ensues.  C.  That  their 
natural  state,  in  the  absence  of  external  impressions,  is  not  con- 
tinued relaxation.  When  the  heart  and  bowels  are  removed 
from  the  body  of  an  animal  immediately  after  death,  they  con- 
tinue for  a  time  alternately  to  contract  and  to  dilate.  7.  That 
an  impression  transmitted  through  the  nerves  does  not  appear 
the  usual  stimulus  to  their  action. 

717.  From  the  experiments  of  the  French  physiologists  it 
would  appear,  that  in  an  animal  deprived  of  all  the  upper  portions 
of  the  brain,  but  in  which  the  medulla  oblongata  is  preserved,  all 
indications  of  the  more  complex  operations  of  thought  disappear, 
but  the  animal  still  remains  capable  of  executing  such  voluntary 
motions  as  are  of  an  instinctive  character,  as,  for  example,  swal- 
lowing.    Animals  deprived  of  the  cerebellum,  provided  the  me- 

,  dulla  oblongata  remains,  and  is  free  from  compression,  not  only 
appear  to  be  capable  of  sensation,  but  give  all  the  usual  indica- 
tions of  intelligence,  and  evidently  exert  volitions,  which  occasion 
the  action  of  many  voluntary  muscles.  But  they  have  lost  the 
power  of  regulating  the  contractions  of  those  muscles  so  as  to 
execute  any  definite  voluntary  action,  excepting  those  which  are 
instinctive.  All  the  other  voluntary  movements  of  the  body  and 
limbs  are  performed  in  so  irregular  a  manner,  that  they  are, ge- 
nerally ineffective  for  the  purposes  for  which  they  are  intended ; 
and  most  of  the  usual  complex  movements  required  for  progres- 
sive motion  cannot  be  performed  at  all.  This  has  been  explained 
by  the  supposition  that  the  animal  has  lost  all  I'ecollection  or 
association  of  those  trains  of  muscular  sensations  which  used  to 
accompany  and  to  guide  these  movements,  inconsequence  of  the 
loss  of  the  cerebral  organs  which  are  instrumental  in  furnishing 
those  associations.  One  of  the  inferences  drawn  from  these  facts 
(which  themselves  require  more  ample  confirmation  before  they 
can  be  regarded  as  established)  is,  that  the  recollection  of  those 
associations  connected  with  voluntary  motion  depends  on  the 
cerebellum,  in  the  same  way  in  which  the  associations  of  sensa- 
tions and  ideas  depend  on  the  hemispheres  of  the  brain. 

718.  It  is  a  remarkable  circumstance  that  injuries  or  diseases 
occurring  in  the  hemispheres  either  of  the  cerebrum  or  cerebellum 
produce  paralysis,  that  is,  destroy  the  power  of  voluntary  motion, 
of  the  muscles  situate  on  the  opposite  side  of  the  body.  This  has 
been  endeavoured  to  be  explained  by  the  alleged  decussation  or 
crossing  of  the  nervous  fibres  of  the  lower  part  of  the  corpora 
pyramidalia  on  each  side.     But  in  order  to  account  for  all  the 

26 


302 


SENSORIAL    FUNCTIONS. 


phenomena  of  this  kind,  we  must  suppose  the  decussation  to  take 
place  between  the  fibres  which  compose  the  posterior  and  the 
anterior  columns  of  the  spinal  cord. 

719.  Although  the  function  of  the  nerves  in  transmitting  impres- 
sions from  the  organs  of  sense  to  the  brain,  which  give  rise  to 
sensation,  and  in  transmitting  impressions  of  volition  from  the 
brain  to  the  muscles  of  voluntary  motion,  which  give  rise  to  the 
contraction  of  those  muscles,  appear  to  be  of  the  same  kind,  and 
to  difler  only  in  the  direction  in  which  the  impression  is  trans- 
mitted, the  question  has  often  been  asked,  whether  the  same 
nervous  filaments  which  transmit  the  one  class  of  impressions  are 
employed  to  transmit  the  other  likewise ;  or  whether  difi^erent 
portions  of  the  nerve  are  appropriate  to  these  different  offices. 
The  truth  of  the  last  of  these  propositions  may  now  be  considered 
as  being  firmly  established. 

720.  The  observations  which  first  suggested  the  idea  of  there 
being  two  sets  of  nervous  filaments,  the  one  subservient  to  sensa- 
tion, and  the  other  to  volition,  were  those  in  which  a  limb  was 
only  partially  paralysed,  the  power  of  motion  being  retained, 
while  that  of  feeling  was  lost.  Experiments  had  also  been  made 
in  which  nerves  that  had  been  divided,  and  had  afterwards  spon- 
taneously united,  were  found  to  have  recovered  the  power  of 
placing  the  muscles  to  which  they  were  distributed  under  the 
command  of  the  will,  but  yet  had  no  power  of  conveying  sen- 
sitive impressions.  Erasistratus  and  Herophilus  had  long  ago 
taught  the  doctrine  of  there  being  two  species  of  nerves  respec- 
tively appropriated  to  these  opposite  functions ;  and  Galen  was 
inclined  to  the  same  opinion,  from  observing  that  both  the  tongue 
and  the  eye  are  supplied  with  two  separate  sets  of  nerves,  the  one 
apparently  subservient  to  sensation,  the  other  to  motion.  But  it 
is  to  Sir  Charles  Bell  and  Magendie  that  the  merit  belongs  of 
bringing  forward  decisive  proofs  of  the  reality  of  this  distinction 
between  nerves  for  sensation  and  nerves  for  motion,  the  idea 
having  before  been  only  loosely  thrown  out  by  speculative  physi- 
ologists as  a  plausible  conjecture. 

721.  It  results  from  this  discovery  that  the  transmission  of 
impressions  in  opposite  directions,  that  is  in  the  one  case  from 
the  extremities  to  the  brain,  and  in  the  other  from  the  brain  to 
the  muscles,  is  effected  by  different  nerves,  or  at  least  by  different 
sets  of  nervous  filaments,  and  that  no  filament  is  capable  of 
transmitting  impressions  both  ways  indiscriminately,  but  always 
in  one  particular  direction.  These  two  kinds  of  filaments 
are,  it  is  true,  conjoined  together  into  one  nerve ;  but  the  ob- 
ject of  this  union  is  not  community  of  function,  but  conve- 
nience of  distribution,  the  two  kinds  of  filaments  still  remain- 
ing distinct  in  their  functions  as  they  are  likewise  distinct  in 
their  origins.  We  know  that  all  the  nerves  connected  with 
the  spinal  cord  have  a  double  origin  ;  that  is,  are  composed  of 


VOLITION    AND    VOLUNTARY    MOTION.  303 

two  nerves,  the  one  proceeding  from  the  anterior,  and  the  other 
from  the  posterior  columns  of  the  spinal  cord.  It  is  found  that 
an  injury  done  to  the  anterior  roots  of  those  nerves  excites  con- 
vulsions in  the  muscles  which  they  supply,  but  does  not  appear  to 
excite  any  sensation  of  pain  in  the  animal  on  which  the  experi- 
ment is  made;  and  the  division  of  those  nerves  is  followed  by  the 
immediate  paralysis  of  those  muscles,  that  is,  by  their  incapability 
of  being  excited  to  contract  by  any  voluntary  efforts.  On  the 
contrary,  the  irritation  of  the  posterior  roots  of  the  same  nerve  is 
attended  with  no  contractions  of  muscles,  but  calls  forth  expres- 
sions of  violent  pain.  The  section  of  these  nerves  is  followed  by 
insensibility  of  the  parts  which  those  nerves  supply,  while  the 
power  of  voluntary  muscular  contraction  remains. 

722.  From  the  symmetrical  situation  of  these  nerves  with 
reference  to  the  spinal  cord,  Sir  Charles  Bell  has  given  them  the 
name  of  the  original,  or  symmetrical  nerves.  They  comprehend, 
of  course,  all  the  spinal  nerves  which  arise  by  double  roots,  the , 
posterior  of  which  has  invariably  a  ganglion  near  its  origin,  while 
the  anterior  branch  has  no  such  appendage.  These  spinal  nerves 
are  distributed  laterally  to  the  two  halves  of  the  body ;  those  of 
the  one  side  having'  no  connexion  with  those  of  the  other.  Sir 
Charles  Bell  ranks  the  fifth  pair  of  the  cranial  nerves  in  the  same 
class  as  the  spinal  nerves ;  considering  its  two  roots  as  composed 
of  filaments,  appropriated  the  one  to  sensation,  the  other  to  motion ; 
the  former  being  provided  with  a  ganglion  near  its  origin,  and 
the  latter  having  no  ganglion.  He  regards  the  third,  probably 
the  fourth,  the  anterior  branch  of  the  fifth,  the  sixth,  the  portio 
dura  of  the  seventh,  and  the  ninth,  as  being  exclusively  motor 
nerves,  distributed  to  the  muscles  of  the  eye-ball,  lower  jaw,  face, 
and  tongue,  and  placing  these  muscles  under  the  control  of  the 
will.  The  ganglionic  portion  of  the  fifth  pair,  on  the  other  hand, 
he  regards  as  the  great  sentient  nerve  of  the  head ;  which  gives 
exclusively  sensibility  to  the  face,  eye-ball,  mucous  membrane  of 
the  nose,  mouth,  and  tongue.  This  nerve  is  in  communication 
with  the  posterior  column  of  the  spinal  cord  ;  whilst  the  motor 
nerves,  above  enumerated,  appear  to  communicate  with  the  ante- 
rior column.  An  exception  to  this  rule,  however,  occui's  in  the 
CE^se  of  the  fourth  pair,  which  has  never  been  proved  to  commu- 
nicate with  the  anterior  column  of  the  spinal  cord.  It  would 
appear  also  that  the  larger  portions  of  the  eighth  pair,  which  seem 
to  be  more  connected  with  the  posterior  than  with  the  anterior 
columns,  are  nerves  both  of  sensation  and  of  motion :  so  that  the 
exclusive  appropriation  of  the  nervous  filaments,  originating  from 
the  different  surfaces  of  the  spinal  cord,  to  motion  or  to  sensation, 
is  perhaps  not  yet  rigidly  demonstrated. 

72.3.  It  is  remarkable  that  the  peculiar  sensations  conveyed  by 
tha  optic,  the  olfactory,  and  the  auditory  nerves,  have  been  found 


S04 


SENSORIAL    FUNCTIONS. 


by  Magendie  to  be  much  impaired,  or  even  entirely  lost,  by  injur- 
ing the  branches  of  the  fifth  pair  of  nerves,  w^hich  also  supplies 
the  respective  organs  to  which  the  above  nerves  appear  to  be 
•  particularly  appropriated.  The  cause  of  this  anomaly  has  not 
yet  been  satisfactorily  explained. 

724.  Sir  Charles  Bell  has  distinguished  another  class  of  nerves, 
which  he  conceives  to  be  altogether  subservient  to  the  function 
of  respiration,  and  to  be  distributed  to  the  muscles  concerned  in 
that  function.  These  he  terms  the  irregidar,  or  the  superadded, 
or  the  respiratory  nerves.  They  arise  by  single  roots  ;  they  pass 
from  one  organ  to  another  in  various  directions,  and  pursue  a 
very  irregular  and  intricate  course,  passing  across  the  nerves 
belonging  to  the  symmetric  system,  occasionally  uniting  with 
them,  and  connecting  together  the  two  halves  of  the  body. 
These  nerves,  according  to  Sir  Charles  Bell,  are  not  under  the 
control  of  the  will,  and  are  not  capable  of  exciting  sensations; 
their  only  office  being  that  of  transmitting  impressions  from  one 
part  to  the  other.  The  nerves  which  strictly  belong  to  this  class' 
are  the  eighth  pair,  the  spinal  accessory  nerves,  the  phrenic,  the 
external  respiratory  nerve  of  Sir  Charles  Bell,  and  the  great 
sympathetics. 

725.  The  first  pair,  or  the  olfatory  nerves,  the  second,  or  the 
optic,  and  the  portio  mollis  of  the  seventh  pair,  are  wholly  nerves 
of  sensation  ;  and  from  the  special  nature  of  the  impression  they 
convey,  may  be  considered  as  forming  a  separate  class  of  nerves. 

726.  Most  nerves  pass  through  ganglia,,  or  are  interwoven  . 
with  others  in  plexuses  before  they  reach  their  destination.  The 
purposes  answered  by  this  intermixture  of  filaments,  which,  in 
either  case,  appears  to  take  place,  is  to  provide  extensive  con- 
nexions between  the  parts  supplied  with  nerves  and  different 
portions  of  the  spinal  cord,  or  medulla  oblongata,  from  which  the 
several  fibres  originate.  Thus  the  sensitive  and  the  motory  fila- 
ments are  intimately  united  in  the  same  nervous  cord,  which  is 
thus  rendered  capajjle  of  performing  all  the  functions  of  nerves. 
Many  hypothetical  uses  have  been  assigned  to  the  ganglia,  which 
appear  to  be  unsupported  by  facts.  Drs.  Gall  and  Spurzheim 
suppose  that  they  contribute  to  increase  the  nervous  power  in 
those  nerves  on  which  they  are  placed  ;  but  there  does  not  seem 
to  be  any  solid  foundation  for  this  opinion. 

727.  Muscular  contractions,  then,  may  be  distinguished,  with 
reference  to  the  nervous  power  which  excites  them  into  four 
classes;  namely,  1.  The  purely  voluntary  motions  ;  2.  The  auto- 
matic motions;  3.  The  instinctive  motions;  4.  The  involuntary 
motions.  We  have  now  fully  considered  the  first  of  these  classes, 
the  purely  voluntary  motions,  which  may  be  defined  to  be  those 
consequent  on  an  effort  of  volition  of  which  the  mind  is  conscious, 
and  which  is  accompanied  by  a  distinct  idea  of  the  end  interi^ed 


AUTOMATIC    MOTIONS.  ^    305 

to  be  accomplished.  No  examples  or  illustrations  are  necessary 
of  motions  belonging  to  this  class,  as  they  are  those  with  which 
■we  are  most  familiar.  We  pass  on  then  to  the  other  classes  in 
the  order  in  which  we  have  enumerated  them. 


Sect.  V. — Automatic  Motions. 

728.  Automatic  motions  are  those  which  consist  of  a  series  of 
actions,  each  of  which  was  originally  the  object  of  a  distinct 
volition  ;  but  which  by  habit,  that  is,  by  repeated  association, 
have  become  linked  together  in  such  a  manner,  that  a  simple  act 
of  volition  is  sufficient,  apparently,  to  renew  the  whole  series, 
without  requiring  any  separate  effort  of  attention  to  each.  Most 
of  the  actions  which  we  daily  perform,  such  as  walking,  speak- 
ing, writing,  or  playing  upon  a  musical  instrument,  afford  exam- 
ples of  automatic  motions,  being  linked  together  by  associations 
which,  far  from  requiring  any  conscious  acts  of  volition,  follow 
one  another  in  a  regular  order  of  sequence  that  cannot  be  broken 
unless  by  the  exertion  of  a  separate  effort  of  attention.  All  these 
movements,  however,  are  still  voluntary,  inasmuch  as  they  re- 
main under  the  control  of  the  will,  which  commands  their  com- 
mencement, can  regulate  their  course,  and  can  stop  them  at 
pleasure. 

729.  The  muscular  actions  required  for  respiration  may  pro- 
bably be  classed  under  this  head.  The  immediate  exciting  cause 
of  the  act  of  inspiration  is  a  sensation  felt  in  the  chest  from  the 
presence  of  venous  blood  in  the  capillary  vessels  of  the  lungs ; 
and  this  sensation,  if  not  speedily  relieved,  increases  rapidly  to 
one  of  extreme  distress,  and  even  agony.  The  influence  of  this 
sensation  in  exciting  the  very  complicated  actions  which  are  ne- 
cessary to  relieve  it  by  drawing  air  into  the  lungs,  and  which, 
indeed,  are  continued  during  sleep,  and  even  when  sensibility  to 
all  other  impressions  appear  suspended,  as  in  the  state  of  apo- 
plexy, is  rendered  manifest  by  the  increased  frequency  and  energy 
with  which  these  actions  are  performed  whenever  any  cause 
exists  obstructing  the  free  access  of  air  into  the  lungs,  and  thus 
augmenting  the  intensity  of  the  sensation. 

730.  Since  the  actions  of  respiration  are  caused,  in  the  first 
instance,  by  sensations,  they  must  be  dependent  on  the  sentient 
nerves  of  the  lungs,  and  especially  on  those  that  establish  the 
most  direct  communication  between  them  and  the  medulla  oblon- 
gata, namely,  the  eighth  pair  of  nerves.  We  find,  accordingly, 
that  after  the  sections  of  those  nerves  the  actions  of  respiration  are 
performed  more  slowly  and  less  perfectly  than  when  entire. 
They,  nevertheless,  continue,  probably  by  means  of  the  other 
communications  which  the  lungs  have  with  the  brain,  through 

26* 


306    (jB.  SENSORIAL    FUNCTIONS. 

the  branches  of  the  great  sympathetic  proceeding  from  the  spinal 
cord.  When  the  part  of  the  medulla  oblongata  from  which  these 
nerves  originate  is  injured,  all  attempts  at  inspiration  are  arrested, 
because  a  final  stop  is  put  to  the  sensation  which  prompts  them. 
The  section  of  the  phrenic  nerves,  or  an  injury  to  the  spinal  cord 
at  any  part  above  the  origin  of  those  nerves,  paralyses  all  the 
respiratory  movements  of  the  chest,  and  thus  occasions  asphyxia 
and  sudden  death. 

731.  When  the  sensation  which  prompts  inspiration,  is  intense 
and  long  continued,  all  the  muscles  performing  movements  auxi- 
liary to  this  act,  such  as  those  which  assist  the  intercostals  in 
elevating  the  ribs,  which  hold  the  glottis  open,  which  raise  the 
velum  pendulum,  which  open  the  mouth,  and  which  expand  the 
nostrils,  are  called  into  simultaneous  action,  and  the  movements 
themselves  are  performed  in  concert,  and  with  perfect  precision. 
These  actions  are  under  the  control  of  the  will,  as  respects  their 
force,  their  rapidity,  and  their  frequency,  and  they  may  even  be 
performed  at  pleasure,  either  separately  or  in  conjunction  ;  unless, 
indeed,  the  sensation  which  prompts  them  be  unusually  intense; 
in  which  case  they  cease  to  be  voluntary  and  automatic,  and 
pass  into  the  class  of  instinctive  motions  we  are  next  to  describe. 
Sir  Charles  Bell  supposes  that  the  nerves  of  all  the  muscles  em- 
ployed in  these  auxiliary  actions  have  peculiar  connexions  among 
themselves  at  their  origin  from  the  lateral  columns  of  the  spinal 
cord,  from  which  the  eighth  pair,  which  is  the  great  sentient 
nerve  of  the  lungs,  also  arise ;  and  that  these  connexions  are  the 
principal  cause  of  their  conjunction  of  action,  whenever  the  sen- 
sation imperiously  demands  that  they  should  act  in  concert.  Yet, 
on  other  occasions,  we  find  that  all  the  muscles  concerned  in 
these  actions,  are  strictly  voluntary  muscles,  and  are  perfectly 
obedient  to  the  will. 


Sect.  VI. — Instinctive  Motions. 

732.  It  is  the  essential  character  of  motions  which  are  strictly 
voluntary,  that  they  are  accompanied  not  only.by  a  consciousness 
of  their  being  performed,  but  also  by  a  corjviction  that  we  may, 
or  may  not  perform  them,  as  we  please ;  or,  to  speak  more  philo- 
sophically, according  as  there  exists  or  not,  a  sufficient  mo/itJe  for 
their  performance.  But  there  are  also,  in  the  healthy  state,  many 
muscles,  of  the  actions  of  which  we  are  always  conscious,  and 
which,  under  ordinary  circumstances,  are  perfectly  obedient  to 
the  will,  but  whose  actions  we  have,  on  other  occasions,  no  direct 
power  of  controlling  by  any  effort  of  the  wilL  They  occasionally 
seem  even  to  be  rebellious  to  its  authority,  and  as  if  they  were 
transferred  to  the  agency  of  some  other  power.     They  are  always 


INSTINCTIVE    MOTIONS.  370 

preceded  by  some  sensation,  as  in  the  case  of  coughing,  sneezing, 
and  vomiting;  or  some  internal  affection  of  the  mind,  whicii  has 
been  termed  emotion,  as  in  the  case  of  laughing  and  weeping  ; 
and  they  take  place  without  any  previous  conception  of  the  object 
they  are  calculated  to  attain,  and  therefore  without  the  previous 
existence  or  operation  of  a  motive.  A  very  large  proportion  of 
the  actions  of  brute  animals  appear  to  belong  to  this  class ;  being 
characterized  hy  the  absence  of  that  train  of  nrental  operations, 
which  imply  the  agency  of  motives,  and  the  previous  knowledge 
of  the  consequences  resulting  from  such  actions ;  operations  which 
are  comprehended  under  the  term  reason,  as  contradistinguished 
from  instinct,  or  blind  and  inexplicable  impulse  derived  from  other 
sources. 

733.  Instinctive  motions  are  distinguished  by  Dr.  Alison  into 
two  kinds,  the  one  comprising  such  as  are  not  only  prompted  by 
an  act  of  which  we  are  conscious,  but  are  also  directed  without 
our  being  aware  of  it  at  the  time,  to  an  end  which  we  desire;  the 
other,  those  in  which  our  actions  are  consequent  indeed  on  a  sensa- 
tion, but  are  prompted  by  a  blind  impulse,  the  consequences  which 
are  to  flow  from  the  action  being  either  unknown  or  disregarded; 
as,  for  instance,  in  gratifying  the  appetites,  guarding  the  eye  from 
danger  by  closing  the  eyelids,  or  the  body  from  falling  by  throw- 
ing out  the  hands.  Dr.  Alison,  in  his  Outlines  of  Physiology,  to 
which  we  are  indebted  for  several  of  the  preceding  remarks  and 
illustrations,  has  very  clearly  treated  of  the  whole  subject  of  the 
functions  relating  to  muscular  motion.  He  farther  remarks  that 
the  instinctive  actions  are  closely  connected  with  the  motions 
which  proceed  directly  from  sensations  on  the  one  hand,  and  with 
the  strictly  voluntary  motions  on  the  other.  In  the  adult  human 
being,  it  is  hardly  possible  to  distinguish  them  from  movements 
which  have  been  prompted  by  reason,  and  become  habitual ;  but 
in  the  infant,  and  in  the  lower  animals,  they  are  easily  recognised, 
being  distinguishable  by  two  marks ;  first,  that  they  are  always 
performed  in  the  very  same  way ;  whereas  actions  which  are 
strictly  voluntary,  and  prompted  by  reason,  although  directed  to 
the  same  end^,  vary  considerably  in  different  individuals;  and, 
secondlv,  that,  however  complicated  the  movements  may  be,  the 
truly  instinctive  actions  are  performed  equally  well  the  first  time 
as  the  last;  whereas  even  the  simplest  of  the  strictly  voluntary 
movements  require  education.  The  complex  acts  of  sucking  and 
deglutition  performed  by  a  newborn  infant  may  be  given  as  exam- 
ples of  strictly  instinctive  motions. 

734.  It  is  important,  however,  in  the  consideration  of  this  sub- 
ject, that  we  bear  in  mind,  that  these  actions,  although  in  them- 
selves instinctive,  are  yet  performed  by  muscles  which  are  at 
other  times  voluntary,  and  whose  nervous  connexions  with  the 
sensorium,  render  it  necessary  for  the  performance  of  these  ac- 


308  SENSORIAL    FUNCTIONS. 

tions,  that  the  muscles  themselves  should  communicate  by  their 
respective  nerves  with  the  sensorium.  We  may  fairly  presume, 
therefore,  that  such  actions  are  immediately  dependent  on  a 
change  taking  place  in  the  sensorium,  through  the  medium  of 
which  alone  the  impression,  which  is  the  occasion  of  the  actions, 
becomes  effective  in  their  production. 

735.  The  same  remark  applies  also  to  those  sensations  which 
arise  from  sympathy,  as  it  is  termed  ;  that  is,  which  are  referred 
to  a  part  of  the  body  very  different  to  that  to  which  the  actual 
irritation  is  applied.  Of  this  kind  is  the  pain  of  the  shoulder  ac- 
companying inflammation  of  the  liver;  pain  of  the  knee  from 
disease  of  the  hip-joint ;  and  itching  of  the  nose  from  irritation  in 
the  bowels.  These  sympathetic  sensations  may  perhaps  be 
explained  by  the  nerves  of  those  corresponding  parts  having 
their  origins  from  the  same  parts  of  the  brain  ;  but  much  yet 
remains  to  be  done  towards  establishing  the  truth  of  this 
hypothesis. 


Sect.  VII. — Involuntary  Motions. 

736.  Under  the  head  of  the  involuntary  motions,  we  mean  to 
comprehend  all  those  muscular  contractions  which  are  performed 
Vi^ithout  the  intervention  of  any  change  in  the  sensorium,  and 
consequently  without  being  attended  with  either  sensation,  con- 
sciousness, or  any  other  mental  change.  The  most  unequivocal 
examples  of  this  class  of  motions  are  those  in  which  muscular 
actions  are  excited  by  irritations  applied  directly  to  the  motor 
nerves  which  are  sent  to  the  muscles  themselves ;  for  although, 
in  the  living  body,  such  irritations  are  usually  accompanied  with 
the  sensation  of  pain,  that  sensation  must  be  regarded  as  an  ac- 
cidental concomitant,  and  not  a  necessary  part  of  the  pheno- 
menon ;  as  is  proved  by  the  absence  of  all  sensation,  when  the 
nerve  has  been  divided  between  the  brain  and  the  part  to  which 
the  irritation  is  applied,  and  yet  the  muscles  in  which  the  nerve 
terminates,  exhibit  the  same  involuntary  contractions  as  before. 
The  same  phenomenon,  indeed,  may  be  reproduced  after  the 
death  of  the  animal,  or  when  the  brain  or  head  has  been  removed. 

737.  Other  cases  are  met  with  of  a  more  complex  and  dubious 
.character;  namely,  those  in  which   muscles  usually  under  the 

influence  of  the  will,  exhibit  contractions  in  consequence  of  irri- 
tations applied,  not  to  their  own  nerves,  but  to  some  more  dis- 
tant part,  which  receives  other  nerves.  It  is  manifest  that  in 
these  instances,  the  irritation  of  these  latter  nerves  produces  an 
impression  which  is  propagated  along  their  course  towards  the 
central  parts  of  the  nervous  system,  and  is  from  thence  again 
transmitted  along  the  course  of  the  nerves  supplying  the  muscles, 


INVOLUNTARY    MOTIONS.  309 

in  which  they  excite  contractions  of  the  same  kind  as  those  ori-^ 
ginating  in  voUtion.  Yet  these  motions  may  tai<e  place  wholly 
independently  of  the  sensorium,  and  are  found  to  occur,  indeed, 
when  all  communication  with  the  brain  is  intercepted.  For  if, 
a  few  seconds  after  an  animal  has  been  deprived  of  life,  the 
spinal  cord  be  divided  in  the  middle  of  the  neck,  and  also  in  the 
middle  of  the  back,  upon  irritating  either  by  a  mechanical  or 
chemical  stimulus,  or  by  the  application  of  heat,  any  sensitiv^e 
portion  of  the  body  connected  by  nerves  with  either  of  these 
isolated  segments,  the  muscles  of  that  portion  of  the  limb,  so  con- 
nected with  the  spine,  are  thrown  into  action.  If,  for  instance, 
the  sole  of  the  foot  be  pricked,  the  foot  is  suddenly  retracted, 
with  the  same  gesture  as  it  would  have  been  during  life,  and  of 
course  with  the  same  apparent  indication  of  suffering.*  It  is 
evident  that  here  an  irritation  applied  to  a  nerve,  the  usual  office 
of  which  during  life  was  to  transmit  impressions  to  the  sensorium 
productive  of  sensations  of  pain,  has  now  produced  an  impression  '' 
which  is  conveyed  to  the  spinal  cord  only ;  but  which  yet  is 
followed  by  the  contractions  of  those  very  same  muscles,  which, 
during  life,  obeyed  the  determinations  of  the  will,  and  produced 
a  motion  of  the  limb  directed  to  its  removal  from  the  cause  of 
injury. 

738.  Phenomena  of  this  description  may  be  observed  more 
readily,  and  are  exhibited  in  a  manner  still  more  marked,  accord- 
ing as  the  animal  on  which  the  experiment  is  made,  occupies  a 
lower  place  in  the  scale.  Among  vertebrated  animals,  the  mo- 
tions just  described,  and  others  of  a  similar  character,  indicative 
of  sensation  and  volition,  are  most  easily  produced  in  reptiles,  as 
in  the  turtle,  the  serpent,  and  the  frog ;  in  which  we  find  that 
isolated  portions  of  the  spinal  cord  perform  functions  analogous 
to  those  of  the  brain,  as  far  as  relates  to  the  receiving  of  impres- 
sions from  a  certain  set  of  nervous  filaments,  and  the  transmitting 
of  impressions  to  other  nervous  filaments,  which  proceed  from 
the  same  part  of  the  spinal  cord,  and  are  distributed  to  the  mus- 
cles. These  two  sets  of  nerves  correspond  in  their  functions  to 
the  sensory  and  motor  nerves  by  which  sensorial  phenomena  are 
produced  (see  §  721).  In  articulated  animals,  whose  spinal  cord 
consists  of  a  series  of  nodules  of  nervous  matter,  resembling 
ganglia,  connected  by  two  longitudinal  cords,  and  severally 
giving  origin  to  their  respective  bundles  of  nerves,  which  radiate 
on  each  side  from  these  ganglia,  as  from  so  many  centres,  the 
capability  of  each  ganglion  to  perform  this  double  function  is 
still  more  susceptible  of  demonstration ;  and  each  segment  of  a 
worm  or  an  insect,  for  example,  appears,  in  consequence,  to 
enjoy  a  separate  life,  and  exhibits  the  semblance  of  possessing 

*  See  Mayo's  Outlines  of  Human  Physiology,  p.  231. 


310  '  SENSORIAL    FUNCTIONS. 

powers  of  sensation  and  voluntary  motion  independently  of  tfie 
rest. 

739.  The  question  now  arises  whether  these  indications  of  sen- 
sorial powers  actually  proceed  from  the  exercise  of  those  facul- 
ties ;  that  is,  whether  they  are  accompanied  by  actual  feeling 
and  actual  volition,  of  both  of  which  consciousness  is  the  essence ; 
or  whether  they  exist  in  appearance  only,  and  without  any  real 
consciousness  on  the  part  of  the  individual  percipient  being.  This 
question,  taken  in  all  its  generality,  it  is  extremely  difficuU,  per- 
haps impossible,  to  decide ;  and  its  solution  involves  that  of 
another  problem,  equally  obscure,  which  is  presently  to  come 
under  our  notice :  namely,  as  to  the  locality  and  extent  of  the 
sensorium  in  all  the  classes  of  the  animal  kingdom.  The  plan  of 
structure,  and  the  vital  constitution  of  articulated  animals,  are  so 
different  from  what  occurs  in  the  system  of  animals  of  the  ver- 
tebrate type,  that  whatever  may  be  the  conclusions  we  may  form 
with  regard  to  the  sensorial  powers  and  the  organs  which  exer- 
cise them  in  the  former  class,  we  are  not  M^arranted  in  extending 
the  same  conclusions  to  the  latter  class  of  beings,  in  all  of  which 
we  cannot  fail  to  recognise  the  most  decided  character  of  indi- 
viduality. It  is  hardly  possible  to  conceive  the  co-existence  of 
two  separate  centres  of  sensation  and  volition  in  any  vertebrate 
animal,  because  we  find  it  impossible  to  understand  how  con- 
sciousness can  be  subdivided  into  portions  corresponding  to  the 
different  segments  into  which  the  spinal  cord  may  be  divided. 
If,  therefore,  we  regard  the  sensorium  as  occupying  any  portion 
of  the  brain,  or  rather  of  the  encephalon,  such  as  the  medulla 
oblongata,  we  cannot  admit  the  existence  of  a  separate  or  acces- 
sary sensorium,  situate  in  any  part  of  the  spinal  cord,  and  capable 
of  exercising  the  sensorial  functions  independently,  when  all 
nervous  communication  with  the  principal  sensorium  is  cut  off. 
If  the  power  of  sensation  could  ever  be  retained,  even  for  a  se- 
cond, after  the  head  has  been  severed  from  the  body,  we  must 
suppose  that  the  seat  of  that  faculty  is  still  in  the  head,  and  not 
in  the  trunk,  the  movements  of  which,  when  excited  by  galvan- 
ism, however  they  may  resemble  those  which  were  performed 
during  life  in  obedience  to  volition,  in  conformity  to  the  design, 
and  prompted  by  motives  arising  from  bodily  sensations,  must 
be  regarded  as  purely  mechanical,  or  rather  as  the  result  of 
mere  nervous  irritation,  and  without  the  existence  of  either  sen- 
sation or  volition  of  any  kind.  We  have  decisive  proofs  that  in 
the  human  system  phenomena  of  this  kind  occur  without  any 
participation  of  the  mind,  that  is,  without  either  sensation,  per- 
ception, or  volition,  in  cases  where,  from  accident,  the  spinal 
cord  has  been  divided  or  compressed  in  the  neck,  or  back,  and 
where  the  muscles  of  the  trunk  that  receive  their  nerves  from 
that  part  of  the  spinal  cord,  which  is  situate  below  the  injury, 


INVOLUNTARY    MOTIONS.  311 

are  affected  with  involuntary  movements.  We  are  therefore 
fairly  entitled  to  extend  the  analogy  to  other  animals  whose  con- 
struction does  not  materially  differ  from  that  of  man,  however 
appearances  may  seem  to  countenance  the  hypothesis  of  the  sen- 
sibility of  the  trunk,  after  its  communication  with  the  brain  has 
been  intercepted. 

740.  Great  confusion  has  been  introduced  into  this  subject  by 
the  inaccurate  language  employed  by  physiologists  in  theorizing 
•on  these  phenomena ;  and  in  using  which  language  they  have  lost 
sight  of  the  essential  distinction  which  should  ever  be  kept  in 
view  between  psychological  and  physical  phenomena.  The  term 
sensibility  should  be  strictly  confined  to  such  properties  as  are 
immediately  connected  with  the  mental  changes  which  are  deno- 
minated sensations,  and  which  are  characterized  by  attendant 
consciousness.  All  other  corporeal  properties  or  phenomena 
which  do  not  produce  these  mental  changes,  are  simply  of  a 
physical  nature,  and  belong  to  another  class  to  which  the  same 
appellation' ought  never  to  be  applied.  Bichat  has  committed  this 
great  error  in  employing  the  term  organic  sensibility  to  denote 
phenomena  of  this  latter  kind  ;  and  the  introduction  of  this  term 
has  led  to  an  interminable  confusion  of  ideas  among  those  who 
have  adopted  his  system,  and  who  have^  been  thereby  led,  from 
this  misapplication  of  terms,  to  some  vague  notion  of  a  pecuhar 
but  obscure  kind  of  actual  sensation,  which  they  attributed  to 
portions  of  the  nervous  system  unconnected  with  the  sensorium, 
independent  of  all  percipience,  and  partaking  of  the  mystical 
doctrines  of  Stahl  and  Von  Helmont  as  to  the  operations  of  their 
supposed  anima  and  archceus.     (See  §  10 J.) 

For  the  dissipation  of  these  clouds  which  have  too  long  ob- 
scured the  ideas  and  perplexed  the  reasonings  of  the  physiolo- 
gists, we  need  only  direct  on  the  subject  the  searching  light  of 
philosophical  analysis,  which  will  render  its  outlines  clear  and 
distinct,  and  enable  us  to  follow  their  various  flexures  and. 
crossings,  and  obtain  more  correct  views  of  the  landscape  in  all 
its  details. 

741.  The  power  exercised  in  the  instances  we  have  described 
by  the  central  parts  of  the  nervous  system,  independently  of  all 
sensorial  phenomena,  is  that  power  which  we  have  already  dis- 
tinguished by  the  term  nervous  power,  in  contradistinction  to  the 
sensorial  power  exercised  by  the  same  system.  (See  §  96,  536, 
537.)  To  Dr.  Wilson  Philip  belongs  the  merit  of  having  first 
clearly  pointed  out  the  distinction  between  these  two  orders  of 
functions,  and  of  having  given  them  specific  appellations.  Dr. 
Marshall  Hall  has  lately  introduced  a  new  term,  that  of /•Cy^e.c 
function,  to  designate  the  series  of  phenomena  consisting  of  the 
transmission  of  impressions  by  certain  nerves  to  the  central  parts 
of  the  nervous  system,  (which  he  limits  to  the  spinal  cordj  and 


312  SENSORIAL    FUNCTIONS. 

the  consequent  transmission  of  an  action  by  the  muscular  nerves, 
^  which  is  followed  by  the  contractions  of  muscles.  To  the  whole 
system  concerned  in  this  function  he  gives  the  name  of  the  excito- 
motory  system;  the  nerves  receiving  the  impressions  he  calls  the 
incident  nerves ;  and  those  conveying  it  to  the  muscles,  the  rejiex 
nerves.^ 

742.  It  would  appear  from  what  has  been  already  noticed 
(§  711),  that  every  muscle  the  action  of  which  is  capable  of  be- 
ing brought  under  the  dominion  of  the  will,  and  which  is  there- 
fore entitled  to  be  classed  among  the  voluntary  muscles,  may 
occasionally  be  made  to  act  by  other  causes,  applied  either  directly 
to  their  own  fibres,  to  the  nerves  distributed  to  them,  or  to  other 
parts  connected  with  them  only  by  the  medium  of  portions  of  the 
brain,spinalcord,orthegangliaof  the  sympathetic:  and  ithasbeen 
conjectured  that  the  sets  of  nervous  fibrils  which  are  instrumental 
in  the  performance  of  these  latter  functions,  are  different  from  those 
which  are  employed  to  transmit  the  impressions  of  sensation  and 
volition.  This  latter  view  is  the  one  adopted  by  Dr.  W.  Philip, 
who  observes  that,  "  however  blended  the  organs  of  the  sensorial 
and  nervous  powers  may  appear  to  be,  we  are  assured  that  they 
are  distinct  organs  by  the  fact,  that  while  the  organs  of  the  ner- 
vous power  evidently  reside  equally  in  the  brain  and  spinal  mar- 
row, those  of  the  sensorial  power  appear  to  be  almost  wholly  in 
man,  and  chiefly  in  all  the  more  perfect  animals,  confined  to  the 
former. "f  It  does  not,  however,  appear  that  we  as  yet  possess 
any  direct  means  of  either  establishing  or  disproving  the  truth  of 
this  supposition. 

743.  There  yet  exists  another  class  of  muscles,  comprehending 
those  which  never,  under  any  circumstances,  become  voluntary. 
To  this  class  belong  the  heart  and  blood-vessels;  the  muscular 
fibres  of  the  excretory  ducts,  and  other  parts  of  the  organs  of 

*  [Dr.  Hall,  whose  views  have  given  rise  to  much  discussion  lately,  pro- 
poses to  divide  the  nerves  into  1,  the  cerebral,  or  the  sentient  and  voluntary: 
2,  the  true  spinal  or  excito-motory,  and  3,  the  ganglionic,  or  the  nutrient  and 
secretory.  If  the  sentient  and  voluntary  functions  be  destroyed  by  a  blow 
upon  the  head,  thesphinctermuscles  will  still  contract  when  irritated,  because 
the  irritation  is  conveyed  to  the  spine,  and  the  reflex  action  takes  place  in  the 
muscle,  so  as  to  throw  it  into  contraction.  But  if  the  spinal  marrow  be  now 
destroyed,  the  sphincters  remain  entirely  motionless,  because  the  centre  of 
the  system  is  destroyed.  Dr.  Hall  is  of  opinion,  that  a  peculiar  set  of  nerves 
constitute,  with  the  true  spinal  marrow  as  their  axis,  the  second  subdivision 
of  the  nervous  system,  and  as  those  of  the  first  subdivision  are  distinguished 
into  sentient  and  voluntary,  these  may  be  distinguished  into  the  excitor  and 
motory.  To  the  cerebral  system  he  assigns  all  diseases  of  sensation,  percep- 
tion, judgment,  and  volition  ;  and  therefore  all  painful,  mental,  and  comatose, 
and  some  paralytic  diseases.  To  the  true  spinal  or  excito-motory  system  be- 
long all  spasmodic  and  paralytic  diseases.  Lectures  on  the  Nervous  System 
by  M.  Hall,  M.D.,  Amer.  edit.  Philad.  1836:  see,  also,  Dunglison's  Ph)'- 
siology,  i.  73.] 

t  Quarterly  Journal  of  Science,  xiv.  93. 


INVOLUNTARY   MOTIONS.  313 

secretion ;  and  the  coats  of  the  stomach  and  of  the  intestines. 
As  the  influence  of  the  nervous  system  on  those  muscles  is  of  a 
very  peculiar  kind,  and  as  their  motions  are  governed  by  different 
laws  from  those  which  regulate  the  voluntary  muscles,  it  will  be 
necessary  to  bestow  on  them  a  separate  consideration. 

744.  M.  Le  Gallois,  in  a  work  entitled  Experiences  sur  le 
Principe  cle  la  Vie,  notamment  sur  celui  des  Mouvemens  du  Cceur, 
et  sur  le  Siege  de  ce  Principe,  thought  he  had  proved  that  the 
muscular  power  of  the  heart  is  derived  altogether  from  the  spinal 
cord,  and  not  from  the  brain.  He  found  that  on  injuring  the 
spinal  cord,  the  heart  is  so  enfeebled  as  no  longer  to  be  capable 
of  propelling  the  blood ;  but  that  the  contractility  of  the  heart  may 
continue  unimpaired  when  the  brain,  and  even  the  whole  head,  is 
removed,  provided  respiration  be  kept  up  by  artificial  inflation  of 
the  lungs.  He  conceived,  therefore,  that  the  use  of  the  cardiac 
nerves  is  to  establish  the  connexion  between  the  spinal  cord  and 
the  heart;  and  that  whenever  the  heart  is  affected  by  passions 
and  emotions  of  the  mind,  which  produce  their  first  changes  on 
the  brain,  it  is  influenced  through  the  medium  of  the  spinal  cord, 
which  is  itself  affected  by  the  brain.  Dr.  Wilson  Philip  has 
shown  the  fallacy  of  this  conclusion ;  and  has  completely  esta- 
blished, by  direct  experiment,  that  under  similar  circumstances, 
the  brain  has  just  as  much  influence  on  the  motions  of  the  heart 
as  the  spinal  cord.  The  motion  of  the  heart  is  no  more  affected 
by  the  removal  of  the  spinal  cord  than  by  that  of  the  brain,  if  the 
same  precautions  be  taken  in  either  case,  of  effecting  the  removal 
slowly,  and  with  as  little  disturbance  to  the  remaining  parts  of 
the  system  as  possible.  If,  on  the  other  hand,  either  the  brain  or 
the  spinal  cord  be  suddenly  crushed  by  a  blow,  which  at  once 
destroys  its  texture,  the  heart  is  instantly  paralysed,  and  its  motions 
cease.  iVlthough  the  muscular  fibres  of  these  organs  are  not 
excited  to  contraction  by  irritations  of  any  kind  applied  to  their 
nerves,  nor  their  contractions  arrested  by  the  section  of  those 
nerves,  yet  these  actions  are  immediately  accelerated  by  the 
application  of  chemical  stimulants,  such  as  alcohol,  either  to  the 
brain  or  to  the  spinal  cord  ;  and  retarded  by  the  application  of 
opium,  tobacco,  or  other  narcotic  agents,  to  the  same  parts. 

745.  It  would  appear,  therefore,  that  although  there  is  no  essen- 
tial difference  between  the  real  nature  of  the  irritability  of  the 
involuntary,  and  that  of  the  voluntary  muscles,  yet  that  each  is 
influenced  by  different  kinds  of  stimuli,  and  by  stimuli  applied 
through  a  different  medium.  Mechanical  stimuli,  such  as  punc- 
tures or  partial  divisions  of  the  fibres  of  the  muscles  of  voluntary- 
motion,  act  on  them  only  through  the  medium  of  their  nerves;  and 
if  applied  to  the  parts  of  the  brain  whence  these  nerves  originate, 
will  throw  those  muscles  into  the  most  violent  spasmodic  contrac- 
tions.    The  heart,  on  the  contrary,  is  but  slightly  disturbed  in  its 

27 


'  314  SENSORIAL    FUNCTIONS. 

movements  by  the  same  kind  of  injury  done  to  the  brain  or  spinal 
cord,  provided  the  injury  be  confined  to  a  small  portion  of  those 
organs.  That  important  organ  appears  to  be  affected  only  in 
proportion  to  the  extent  of  the  parts  that  have  suffered  injury,  and 
to  the  suddenness  vv^ith  which  that  injury  has  been  inflicted;  as  is 
exemphfied  by  wounding  the  brain  rapidly  in  many  directions. 
Chemical  stimuli,  on  the  contrary,  applied  to  any  part  of  the  brain 
or  spinal  cord,  produce  considerable  and  immediate  increase  of 
the  action  of  the  heart  i  while  the  voluntary  muscles  continue  all 
the  while  unaffected ;  and  the  animal  betrays  no  sense  of  pain. 
Accordingly  the  heart,  having  no  direct  dependence  on  any  part 
of  the  nervous  system,  may  continue  its  action  when  the  brain 
and  spinal  cord  are  destroyed,  and  even  when  it  is  itself  removed 
from  the  body.*  The  nerves  with  which  it  is  supplied,  however, 
render  it  capable  of  being  influenced  through  those  causes,  as,  for 
example,  by  the  passions,  and  by  various  poisons,  which  effect  a 
considerable  portion  of  the  nervous  system. 

746.  The  contractile  powers  of  the  other  parts  of  the  vascular 
system,  and  most  of  the  secreting  organs,'as  well  as  the  irritability 
of  the  stomach  and  intestines,  are,  like  those  of  the  heart,  indepen- 
dent of  the  nervous  system,  yet  capable  of  receiving  an  influence 
through  the  medium  of  the  nerves;  and  the  same  law  appears  to 
extend  generally  to  all  the  involuntary  muscles.  The  extensive 
nervous  communications  which  are  naturally  established  between 
the  whole  system  of  involuntary  muscles,  and  the  organs  in  which 
they  enter,  seem  to  be  necessary  in  order  that  any  one  set  of  these 
organs  should  be  subjected  to  the  influence  of  all  the  others.  This 
purpose  is  effected  by  that  complex  arrangement  of  nerves,  which 
has  been  termed  the  ganglionic  system,  from  the  great  number  of 
ganglia  annexed  to  them.  The  great  sympathetic  nerve  forms 
the  principal  connecting  nerve  in  this  system  between  all  the 
muscles  of  involuntary  motion;  which,  through  the  medium  of 
filaments  from  the  extensive  chain  of  ganglia  belonging  to  this 
nerve,  are  placed  in  connexion  with  every  part  of  the  brain  and 
spinal  cord.  Each  ganglion  belonging  to  the  sympathetic  system 
has  been  considered  as  a  secondary  centre  of  nervous  influence, 
receiving  supplies  from  all  the  latter  parts,  and  conveying  to  the 
former  organs  the  united  influence  of  the  nervous  system  in 
general.  The  muscles  of  voluntary  motion,  on  the  other  hand, 
are  subjected  to  the  influence  of  only  small  portions  of  these  cen- 
tral parts  of  the  nervous  system,  and  receive  their  nerves  directly 
from  those  parts;  and  usually  without  the  intervention  of  ganglia, 
and  with  comparatively  few  intermixtures  of  nervous  filaments ; 
such  intermixtures  being  designed  for  the  purpose  of  effecting 
combinations  with  the  nerves  of  sensation,  and  especially  with 
those  which  convey  impressions  relative  to  muscular  motion. 

*  [See  §  450,  note.] 


PSYCHOLOGICAL    RELATIONS,  315 

747.  The  ganglia  of  the  sympathetic  system  have,  accordingly, 
been  considered  by  many  physiologists  as  performing  functions 
similar  to  those  of  the  portions  of  the  spinal  cord  exercising  mere 
nervous  power ;  that  is,  in  the  language  of  Dr.  Marshall  Hall, 
performing  reflex  functions,  and  belonging,  together  with  the 
branches  of  the  sympathetic  nerve,  to  the  excito-motory  system.* 


Sect.  VIII. — Psychological  Relations  of  the  Sensorium. 

748.  In  treating  of  the  functions  of  the  nervous  system  which 
involve  operations  both  of  the  body  and  of  the  mind,  it  is  very 
diflicult  to  draw  the  strict  line  of  distinction  between  them,  and 
avoid  treating  of  subjects  which  properly  belong  to  metaphysics. 
We  have  endeavoured,  in  the  preceding  account  of  the  physio- 
logy of  man,  to  confine  ourselves  strictly  to  the  consideration  of 
the  corporeal  changes  which  accompany  the  different  mental 
affections,  and  to  avoid,  as  much  as  possible,  encroaching  upon 
the  province  of  the  metaphysician.  That  certain  physical 
changes  take  place  in  some  portion  or  other  of  the  cerebral  mass 
in  connexion  with  various  mental  changes,  we  have  the  clearest 
evidence :  but  of  the  nature  of  these  physical  changes  we  are 
wholly  ignorant ;  nor  does  the  present  state  of  our  information 
afford  a  shadow  of  hope  that  we  shall  ever  gain  any  more  pre- 
cise knowledge  of  them.  The  mental  changes,  on  the  other  hand, 
constitute  a  distinct  and  separate  branch  of  science  ;  to  the  know- 
ledge of  which  we  arrive  by  channels  totally  different  from  those 
which  instruct  us  relatively  to  the  former  ;  namely,  by  conscious- 
ness, and  by  reflexion  on  the  series  of  phenomena  furnished  to  us 
by  consciousness.  These  two  subjects  of  study,  the  material  and 
the  immaterial,  however  numerous  may  be  the  subtle  and  inscru- 
table links  that  connect  them,  constitute  two  worlds,  which  in 
our  conception  must  for  ever  remain  totally  distinct ;  nor  is  it 
even  possible  for  us  to  conceive  how  any  knowledge  which  we 
can  obtain  with  relation  to  any  physical  changes  in  our  corporeal 
frame,  or  any  physiological  laws  that  may  regulate  the  succes- 
sion of  those  changes,  can  in  the  smallest  degree  assist  us  in 
understanding  the  phenomena  of  intellect,  and  the  affections  of 
the  soul. 

749.  The  brain  has  been  very  justly  regarded  as  the  organ  of 
the  mind ;  that  is  the  corporeal  instrument  invariably  employed 
in  the  operations  of  the  mind.  This  is  a  necessary  corollary  from 
the  proposition  that  no  mental  operation  can  take  place  without 
the  co-existence  of  some  physical  change  in  the  brain.     But  a 

*  See  Grainger's  Observations  on  the  Structure  and  Functions  of  the 
Spinal  Chord, 


316  SENSORIAL    FUNCTIONS. 

s6cond  proposition,  the  converse  of  the  former,  has  been  advanced ; 
namely,  that  the  mental  operations  are  the  "  functions  of  the  brain." 
But  this  latter  proposition  would  be  true  only  on  the  supposition 
that  the  physical  change  in  the  brain,  and  the  corresponding 
mental  change  of  which  we  are  conscious,  are  one  and  the  same 
thing.  Until  this  fundamental  doctrine  of  materialism,  namely, 
the  identity  of  matter  and  mind,  be  proved,  we  cannot  include 
under  the  functions  of  the  brain,  both  the  mental  changes  and 
the  corporeal  changes.  The  physiological  office,  or  function  of 
the  brain  is  the  production  of  certain  corporeal  changes,  connected 
in  some  inexplicable  manner  with  certain  mental  changes  ;  which 
two  classes  of  changes  are  in  their  nature,  as  far  as  we  are  capable 
of  forming  any  conceptions  of  them;  radically  and  essentially  dif- 
ferent from  each  other. 

•750.  The  ambiguity  of  ordinary  language  is,  indeed,  a  frequent 
source  of  confusion  of  ideas  on  this  subject.  We  speak  correctly 
when  we  say  that  the  eye  is  the  organ  of  vision,  because  it  is  an 
instrument  without  which  vision  could  not  be  exercised  ;  but  were 
we  to  regard  vision  as  the  function  of  the  eye  alone,  we  should 
evidently  be  guilty  of  inaccuracy  in  extending  too  far  the  purpose 
of  that  instrument.  The  function  of  the  eye  is  to  produce  certain 
impressions  upon  the  retina,  which  impressions  are  but  links  in  the 
series  of  changes,  of  which  only  the  last  constitutes  vision.  These 
impressions  made  on  the  retina  are  followed  by  changes  in  the 
course  of  the  optic  nerves,  and  these  again  by  changes  in  the 
sensorium.  The  function  of  the  optic  nerves,  and  of  that  part  of 
the  sensorium  in  which  they  terminate,  is  the  production  of  these 
physical  changes.  Vision,  an  affection  of  the  mind,  is  undoubt- 
edly the  effect  of  these  physical  changes ;  but  is  not  properly  the 
function  of  any  of  these  organs,  except  the  term  function  be  used 
in  that  loose  and  popular  sense,  in  which  it  is  made  to  embrace 
all  the  remote  consequences  of  the  phenomena,  in  the  production 
of  which  the  organ  in  question  is  concerned.  In  this  sense,  indeed, 
vision,  and  all  the  mental  affections  consequent  upon  vision,  might 
certainly  be  said  to  be  functions  of  the  eye ;  but  in  the  strict  phi- 
losophical sense,  the  function  of  the  eye  is  limited  to  the  formation 
of  images  on  the  retina,  and  the  impressions  thereby  received  by 
the  retina ;  and,  in  like  manner,  the  proper  function  of  the  brain 
is  the  production  of  certain  physical  changes  in  the  fabric  of  the 
brain,  consequent  upon  certain  impressions  made  on  the  nerves 
by  external  causes,  and  consequent  also  upon  certain  internal 
affections  of  the  mind,  which  are  capable  of  exerting  on  it  this 
influence. 

751.  The  affections  of  the  mind  are  very  various  and  compli- 
cated ;  a  great  multitude  of  ideas  and  associations  are  treasured 
up  in  it,  and  constitute  a  variety  of  powers,  of  faculties,  of  pro- 
■  pensities,  of  instincts,  and  of  passions.     The  conformation  of  the 


SLEEP. 


317 


brain,  which  is  the  organ  of  the  mind,  is  also  very  complex,  and 
appears  to  consist  of  an  assemblage  of  different  parts,  constructed 
evidently  with  extreme  refinement,  and  arranged  with  great  care, 
and  with  very  elaborate  design.  The  idea  naturally  suggests 
itself,  that  these  different  portions  recognised  by  the  anatomist, 
may  perhaps  have  some  correspondence  with  the  several  facul- 
ties into  which  the  phenomena  of  the  mind  have  been  analyzed 
by  the  metaphysician.  This  question  has  indeed  been_  often 
started,  and  is  quite  distinct  from  that  of  the  materiality  or  imma- 
teriality of  the  soul ;  for  it  is  perfectly  conceivable  that  if  the 
immaterial  soul  acts  by  means  of  material  organs,  and  receives 
impressions  from  those  organs,  its  different  operations  may 
require  different  organs.  But  this  subject,  together  with  the 
theories  to  which  it  has  given  rise,  are  amply  discussed  in  the 
Appendix  on  Phrenology. 


Sect.  IX. — Sleep. 

752.  Whilst  the  functions,  which  have  for  their  object  the  re- 
paration of  the  state  of  the  body,  and  which  include  assimilation, 
absorption,  circulation,  respiration,  secretion,  and  nutrition,  con- 
tinue in  constant  activity,  all  those  connected  with  sensation  and 
volition  require  intervals  of  repose,  and  cannot  be  maintained 
beyond  a  certain  time  without  great  exhaustion  of  the  nervous 
power.  These  periodical  intermissions  in  the  activity  of  the 
animal  functions,  so  necessary  for  the  renovation  of  the  power 
on  which  they  are  dependent,  constitute  sleep.  The  eye-lids 
close  to  protect  the  eye  from  injury,  and  the  eye-ball  is  turned 
upwards ;  the  external  senses  and  all  the  active  intellectual  oper- 
ations are  suspended;  the  voluntary  muscles  are  relaxed;  and 
we  become  insensible  to  all  external  impressions.  The  movement 
of  the  involuntary  muscles  continues,  though  with  somewhat  less 
energy  than  during  our  waking  hours.  The  heart  beats  with 
diminished  force  and  frequency,  and  the  muscles  of  respiration 
act  more  slowly ;  but  the  inspirations  are  more  full  and  deep,  and 
the  secretions  are  in  general  less  abundant ;  but  digestion  and 
absorption  are  carried  on  with  great  activity.  The  power  of 
sensation,  though  blunted,  is  not  altogether  lost  during  sleep,  as 
is  proved  by  the  continuance  of  that  part  of  the  movements  of 
the  muscles  of  respiration,  which  depend  on  sensation.  Instinc- 
tive movements  of  the  hmbs,  producing  a  change  of  posture, 
frequently  take  place  from  an  obscure  sensation  of  constraint  at 
their  continuing  long  in  the  same  position.  Any  unusual  impres- 
sions made  on  the  organs  of  the  senses  are  felt  during  sleep,  and 
even  remembered ;  and,  if  the  impression  be  sufficiently  vivid. 
will  interrupt  sleep. 

27* 


318  SENSORIAL    FUNCTIONS. 

753.  Neither  is  the  mind  wholly  inactive  during  sleep ;  it  is 
still  occupied  with  a  succession  of  ideas,  which  is  often  more 
rapid  than  when  we  are  awake ;  the  imagination  is  even  more 
vividly  exerted,  and  the  images  that  pass  before  the  mind  are 
considered  as  realities.  This  constitutes  dreaming,  a  state  which 
is  characterized  also  by  the  pecuhar  circumstance  of  the  want  of 
all  voluntary  power  of  directing  the  succession  of  ideas.  Trains 
of  ideas  and  images  commence  and  follow  one  another,  being 
indissolubly  linked  together  by  those  laws  of  association  which 
are  independent  of  volition. 

754.  An  extraordinary  modijfication  of  dreaming  occurs  in 
what  is  called  somnambulism,  or  sleep-walking;  where  the  will 
recovers  a  certain  degree  of  power  over  the  mental  operations, 
and  over  the  voluntary  muscles  both  of  speech  and  motion,  whilst 
the  body  is  still  less  capable  of  receiving  external  impressions 
than  in  ordinary  sleep.  In  this  peculiar  kind  of  sleep,  the  insen- 
sibility to  most  external  impressions  is  so  profound,  that  it  is 
scarcely  possible  to  awaken  the  person  without  employing  a  con- 
siderable degree  of  violence.  When  at  length  he  does  awake, 
which  often  happens  as  suddenly  as  from  natural  sleep,  he  usually 
retains  little  or  no  recollection  of  what  happened  to  him,  or  of 
what  he  did  whilst  in  this  singular  state. 

755.  A  state  very  similar  to  that  of  natural  somnambulism,  is 
induced  in  some  nervous  constitutions,  especially  those  of  young 
females,  by  certain  manipulations  which  produce  a  long-continued 
reiteration  of  impressions  made  on  the  senses,  and  which  proba- 
bly act  through  the  medium  of  the  mind.  These  have  been 
ascribed  to  a  special  agency,  termed  Animal  Magnetism,  or 
Mesmerism.*- 


CHAPTER    XVIII. 

THE     VOICE. 

756.  The  function  of  the  voice,  and  its  modulation  into  articu- 
lated sounds,  by  which  it  is  rendered  subservient  to  speech,  has 
been  already  pointed  out  as  an  important  part  of  the  animal 

*  [The  whole  history  of  animal  magnetism  exhibits  that  impressible  per- 
sons may  have  hysterical  or  hysteroid  irregularities  of  nervous  distribution 
induced  through  the  medium  of  the  senses,  especially  through  those  of  vision 
and  touch  ;  but  there  is  no  adequate  evidence  to  shovi%  that  the  effects  can  be  in- 
duced without  impressions  being  made  on  some  organ  of  sense;  or  that  there 
is  any  special  agency  of  the  Idnd  that  has  been  imagined.  The  clairvoyance 
or  lucidity  of  vision  of  the  magnetized  is  a  delusion, — perhaps  in  all  cases  a 
deception.] 


THE    VOICE.  319 

economy  of  a  being  designed,  as  man  evidently  is,  to  hold  exten- 
sive communion  with  his  fellow-creatures,  and  effect  the  rapid 
interchange  of  ideas  and  feelings,  through  the  medium  of  the 
sense  of  hearing  (§  24). 

757.  In  order  to  understand  the  mode  in  which  articulate 
sounds  are  produced,  it  will  be  necessary  again  to  advert  to  the 
principles  of  acoustics,  of  which  a  brief  account  was  given  in 
introducing  the  subject  of  the  physiology  of  hearing,  (§  623.) 
The  object  to  be  accomplished  in  the  function  of  the  voice  is 
the  production,  not  so  much  of  single  sounds,  (such  as  those 
which  result  from  single  impulses  given  to  the  air,)  but  of  con- 
tinued sounds,  composed  of  reiterated  vibrations,  repeated  at 
short  and  equal  intervals,  and  constituting  a  musical  note.  There 
are  two  principal  modes  in  which  such  sounds  are  produced ;  the 
one,  that  which  is  practised  in  stringed  musical  instruments,  in 
which  the  impulses  are  given  to  the  air  by  the  vibrations  of  solid 
bodies,  which  are  generally  chords  having  different  degrees  of 
tension ;  and  the  other,  such  as  is  adopted  in  wind  instruments, 
where  the  air  is  thrown  into  undulations  at  regular  intervals,  by 
alternations  of  expansion  and  condensation,  generally  taking 
place  during  the  passage  of  a  stream  of  air  through  a  cavity  in 
which  it  suffers  certain  reflexions  and  reverberations,  alternately 
impeding  and  promoting  its  progress.  In  many  cases  the  effect 
is  obtained  by  a  combination  of  both  these  means,  as  in  a  haut- 
boy, where  an  elastic  plate,  or  reed,  is  placed  in  the  course  of 
the  air  which  is  passing  along  a  tube,  capable  by  its  form  of 
producing  a  musical  note,  independently  of  such  addition. 

758.  In  the  construction  of  the  vocal  organs  of  man,  nature 
has  resorted  to  combinations  of  this  kind.  Advantage  is  taken 
of  the  function  of  respiration  to  convert  the  passages  through 
which  the  air  is  admitted  to,  and  expelled  from  the  lungs,  into  a 
sounding  instrument;  by  adapting  to  the  upper  part  of  the 
trachea,  a  curious  mechanism,  consisting  of  a  frame-work  of 
elastic  cartilages,  with  an  apparatus  of  ligaments,  muscles,  mem- 
branes, and  mucous  glands,  the  assemblage  of  which  is  termed 
the  lai'ynx.  The  aperture  through  which  the  air  passes  is  deno- 
minated the  glottis.  Here  it  is  that  the  breath  is  vocalised ;  that 
is,  rendered  not  only  sonorous,  but  also  modulated  in  its  pitch,  so 
as  to  give  rise  to  a  musical  sound.  Modifications  are  subse- 
quently impressed  on  these  sounds,  by  the  changes  which  the 
undulations  are  made  to  undergo  in  the  cavities  of  the  pharynx, 
of  the  nostrils,  and  of  the  mouth,  according  to  the  various  forms 
and  dimensions  given  to  those  cavities  by  the  motions  of  the 
muscles  of  the  pharynx,  the  velum  pendulum,  the  uvula,  the 
tongue,  the  cheeks,  and  the  lips ;  and  according  to  the  obstacles 
placed  in  the  way  of  the  passage  of  the  air  by  the  movements  of 


320 


SENSORIAL    FUNCTIONS. 


these  parts,  and  the  application,  in  particular,  of  the  tongue  and 
of  the  lips  to  the  palate  and  to  the  teeth. 

759.  The  cartilages  of  the  larynx  are  five  in  number,  namely, 
the  thyroid,  the  cricoid,  the  two  arytenoid,  and  the  epiglottis. 
The  thyroid.,  which  is  also  called  the  scutiform,  or  shield-like 
cartilage,  is  placed  at  the  upper  and  fore-part  of  the  larynx,  and 
is  the  largest  of  the  whole.  It  consists  of  two  lateral  wings  of  a 
quadrangular  form,  uniting  in  front  in  a  longitudinal  angle,  which 
is  felt  projecting  in  the  fore-part  of  the  throat,  and  has  obtained 
the  name  of  the  pomum  adami.  From  the  posterior  corners,  four 
pi'ocesses  project,  called  its  cornua,  distinguished  into  two  superior, 
and  two  inferior.  The  cricoid,  annular,  or  ring-like  cartilage,  is 
placed  below  and  behind  the  former ;  and  it  has  four  articular 
surfaces,  two  below,  for  its  connexion  with  the  inferior  cornua  of 
the  thyroid  cartilage,  and  two  above,  for  the  articulation  of  the 
arytenoid  cartilages,  which  are  bodies  of  a  pyramidal  shape, 
much  smaller  than  the  rest,  and  placed  one  on  each  side,  upon 
the  upper  posterior  and  lateral  parts  of  the  cricoid  cartilages, . 
They  give  attachment  to  ligaments,  and  compose  a  part  of  the 
sides  of  the  opening  called  the  glottis.  The  whole  passage  is 
lined  internally  by  a  delicate  mucous  membrane. 
\  760.  The  epiglottis  is  a  cartilaginous  lid,  which  has  a  pointed 
shape,  resembling  the  leaf  of  an  artichoke.  It  is  fixed  at  its  base 
to  the  OS  hyoides,  to  the  thyroid  cartilage,  and  to  the  root  of  the 
tongue  ;  and  hangs  obliquely  backwards  over  the  opening  of  the 
glottis,  which  extends  in  a  line  from  behind  forwards,  and  is 
formed  by  the  approximation  of  the  vocal  ligaments,  or  chordce 
vocales.  These  ligaments,  which  consist  of  fibres  endowed  with 
a  high  degree  of  elasticity,  are  covered  with  the  fine  membrane 
which  invests  the  whole  of  this  delicate  apparatus,  and  extends 
down  the  trachea  into  the  lungs,  and  above  to  the  posterior 
fauces.  These  are  attached  together  in  front  to  the  thyroid 
cartilage,  and  behind  to  the  arytenoid  cartilages,  where,  in  the 
relaxed  condition  of  the  organ,  they  are  at  some  distance  from 
each  other,  so  as  to  leave  a  triangular  opening  for  the  passage 
of  the  air.  The  effort  to  speak,  or  to  utter  a  vocal  sound,  com- 
mences with  the  action  of  certain  muscles,  more  particularly  the 
crico-thyroidcei,  which  stretch  the  vocal  ligaments,  and  the  crico- 
arytcBUoidei  laterales,  and  the  arytcBUoidci  transversi  and  obliqui, 
which  conspire  to  make  the  arytenoid  cartilages  approximate. 
By  these  combined  actions,  the  vocal  ligaments  are  brought  near 
to  each  other,  in  parallel  directions,  so  that  the  interval  between 
them  or  rima  glottidis,  as  it  is  called,  is  reduced  to  a  mere  nar- 
row linear  fissure. 

761.  When,  therefore,  the  air  is  forcibly  propelled  from  the 
lungs  through  the  glottis,  whilst  the  vocal  chords  are  in  this  ap- 
proximated position,  different  vocal  sounds  will  be  produced,  ac- 


THE    VOICE. 


321 


cording  to  the  degree  of  tension  which  is  given  to  the  chordae 
vocales.  The  greater  the  tension  of  these  ligaments,  the  more 
frequent  will  be  their  vibrations,  and  the  higher  the  pitch  of  the 
note  they  produce.  The  loudness  of  the  sound  ennitted  is  pro- 
portioned, not  to  the  frtiquency  of  the  vibrations,  but  to  their 
extent,  or  the  naagnitude  of  the  excursions  made  by  the  vocal 
chords  in  vibrating.  The  varied  degrees  of  tension  which  can 
be  imparted  at  will,  and  instantaneously,  to  the  vibrating  liga- 
ment of  the  larynx,  by  the  finely  regulated  actions  of  their  differ- 
ent niuscles,  constitute  the  chief  source  of  superiority  in  the  vocal 
organ  to  any  instrument  of  human  invention. 

762.  The  muscles  above  enumerated  as  giving  tension  to  the 
vocal  ligaments,  and  closing  the  glottis  by  the  approximation  of 
the  arytenoid  cartilages,  are  opposed  by  their  antagonists  the 
tiiyreo-arytcenoidei,  which  relax  the  vocal  ligaments,  and  place 
them  in  the  vocalizing  position,  and  by  the  crico-arytcenoidei 
postici,  which  separate  the  arytsenoid  cartilages,  and  thereby 
open  the  glottis.  Thus  the  instrument  we  are  considering  is 
capable  of  an  infinite  number  of  changes  of  form,  and  susceptible 
of  the  finest  modulation. 

763,  It  should  be  stated,  however,  that  many  physiologists 
have  maintained  that  the  musical  tones  of  the  voice  depend,  not 
merely  on  the  tension  of  the  vocal  ligaments,  but  also  on  the  size 
and  form  of  the  aperture  through  which  the  stream  of  air  is^ 
propelled,  and  that  the  larynx  partakes  as  much  of  the  properties 
of  a  wind  as  of  a  stringed  instrument.  The  principal  advocate 
of  this  opinion  was  Dodart,  whose  first  paper*  contains  a  histori- 
cal account  of  the  views  on  this  subject  taken  by  the  earlier 
physiologists.  His  chief  antagonist  in  this  controversy  was 
Ferrein,-|-  who  compares  the  larynx  to  a  violin,  or  harpsichord, 
and  conceives  that  the  voice  is  produced  by  the  vibrations  of  the 
edges  of  the  ligaments  of  the  glottis ;  and  compares  the  action  of 
the  air  to  that  of  a  bow  setting  these  parts  into  vibration.  The 
hypothesis  of  Dodart  has  been  adopted  by  Blumenbach,  who 
conceives  the  action  of  the  larynx  to  be  analogous  to  that  of  the 
flute.  But  the  generality  of  physiologists  consider  the  action  of 
the  ligaments  of  the  glottis  to  be  vibration,  and  similar  to  that  of 
strings  resounding  by  their  tension  alone.  Such  is  the  view  taken 
of  the  subject  by  Dr.  Young4  Sommerring,§  Magendie,||  WilUs,1[ 
and  Mayo,**  who  all  maintain  that  the  voice  depends  on  the 
vibration  of  the  chords  ;  the  frequency  of  which  must,  according 

*  Memoires  de  I'Academie,  pour  1700,  p.  244;  1707,  p.  66. 

t  Ibid,  pour  1741,  pp.  409,  416,  422. 

X  Lectures,  p.  400,  and  Philosophical  Transactions  for  1800,  141. 

§  De  Corporis  Humani  Fabrica,  vi.  93.  H  Physiologie,  i.  196. 

•[  Cambridore  Philosophical  Transactions,  iii.  231. 

**  Human  Physiology,  3d  edit.  p.  350. 


323 


SENSORIAL    FUNCTIONS. 


to  all  acoustic  principles,  be  regulated  solely  by  the  tension  of 
the  chords. 

764.  Dr.  Willis  observes  that,  for  the  production  of  laryngeal 
sounds,  something  more  is  requisite  than  a  definite  tension  of  the 
vocal  ligaments.  He  has  shown,  by  experiment,  that  in  order 
that  the  edges  of  two  membranes,  such  as  those  made  of  leather 
or  of  Indian  rubber,  opposed  to  each  other  with  a  narrow  interval, 
may  vibrate,  the  parts  of  the  membrane  near  their  edges  must  be 
brought  paralled  to  each  other.  Comparing  this  disposition  of 
membrane  in  his  experiment  with  the  parts  of  the  larynx,  he 
supposes  that  the  latter  will  not  vocalize,  unless  some  change, 
independent  of,  and  superadded  to,  the  tension  of  the  ligaments, 
be  produced  in  their  relative  position. 

765.  The  experimental  proof  on  which  Mr.  WiUis  founds  his 
conclusion  that  some  change  in  the  relative  position  of  the  vocal 
chords  is  necessary  to  produce  an  audible  vocal  sound,  is  the 
following.  If  the  finger  be  placed  upon  the  membrane  which 
intervenes  between  the  thyroid  and  cricoid  cartilages,  their  approx- 
imation or  increased  remoteness  may  readily  be  felt.  Now  their 
approximation  being  produced  by  the  action  of  the  crico-thyroid 
muscles,  involves  an  increased  tension  of  the  ligaments.  But  it 
is  possible  by  an  effort  to  keep  these  cartilages  approximated, 
whilst  something  is  still  wanting  in  the  internal  arrangement  of 
the  larynx,  to  fit  it  for  the  production  of  sound.  When  the  thyroid 
and  cricoid  cartilages  are  thus  approximated,  and  the  ligaments 
thus  shown  to  be  in  a  state  of  tension,  if  air  be  impelled  through 
the  larynx,  sound  does  not  necessarily  follow ;  the  ligaments  have 
still,  Mr.  Willis  concludes,  to  be  placed  in  the  vocalizing  position.* 

766.  There  are  still  other  parts  of  the  vocal  apparatus  con- 
nected with  the  sounds  produced  at  the  larynx,  which  require  to 
be  adverted  to.  Amongst  these  the  varying  conditions  of  the 
trachea  appear  to  have  the  greatest  influence  on  those  sounds, 
and  of  this  influence  Mr.  Wheatstone  proposes  the  following 
theory  :f 

"  Such  a  vibrating  apparatus  as  we  have  described  the  ligaments 
of  the  glottis  to  compose,  is  by  itself  capable,  from  the  varying 
tension  of  those  ligaments,  of  producing  all  those  sounds  of  which 
we  find  the  voice  to  be  susceptible.  But  the  intervention  of  a  tube 
between  the  lungs  and  the  larynx,  must  necessarily  exercise  an 
important  influence  on  the  voice,  though  it  has  never  yet  been 
taken  into  consideration.  For,  if  we  unite  such  an  apparatus,  or 
a  free  reed,  which  may  serve  as  a  substitute  for  it,  with  a  tube 
(supposing  it  for  the  moment  fixed  to  a  determinate  degree  of 
pitch),  it  is  found,  that,  unless  the  column  of  air  in  the  tube  is  of 

*  See  Mayo's  Outlines  of  Human  Physiology,  3d  edition,  p.   350,  351, 
from  which  the  above  account  of  Willis's  theory  is  extracted. 
t  Ibid.  p.  252. 


THE    VOICE.  323 

such  a  length  as  to  be.  separately  capable  of  producing  the  same 
number  of  vibrations,  the  sound  cannot  be  obtained  in  its  greatest 
force  and  purity,  and  that  when  the  tube  is  half  this  length,  the 
discordance  between  the  tube  and  the  reed  is  so  great,  as  to  prevent 
the  production  of  the  sound :  between  these  limits  the  sound  is 
intermediate  in  intensity  and  quality.  This  influence  of  the  tube 
is  by  experiment  found  to  be  the  same,  whether  the  tube  be  placed 
after  the  reed,  as  in  several  wind  instruments,  or  before  it,  as  in 
the  vocal  organ.  We  will  now  suppose  the  tube  to  be  unaherable 
in  its  length,  and  the  reed  necessarily  to  undergo  all  its  varying 
modifications  of  pitch;  the  sounds,  instead  of  being  of  even  quality, 
will  be  irregular  in  intensity,  and  require  different  degrees  of 
effort  to  produce  them,  whilst  in  some  parts  of  the  scale,  they 
will  be  totally  extinguished.  All  this  may  be  prevented,  and  the 
utmost  regularity  obtained,  by  shortening  the  tube,  in  proportion 
as  the  vibrations  of  the  reed  increase  in  frequency.  The  trachea 
is  obviously  incapable  of  changing  its  length  within  limits  suffi- 
ciently considerable  to  serve  this  purpose ;  but  Savart's  experi- 
ments have  shown,  that  a  tJibe  of  constant  length  may  be  made  to 
produce  a  great  range  of  sounds,  by  making  it  of  elastic  sides 
susceptible  of  variable  tension.  The  analogy  between  such  a 
tube  and  the  trachea  is  perfect." 

767.  One  mode  of  giving  increased  tension  to  the  windpipe  is 
the  action  of  the  transverse  muscular  fibres  which  bind  the  ends 
of  its  cartilages  together.  Another  is  the  elevation  of  the  larynx, 
which  follows  in  so  remarkable  a  degree  the  elevation  of  the 
pitch  of  the  voice.  Practice  in  singing  improves  the  voice,  partly 
by  giving  us  a  more  ready  command  over  the  tension  of  the 
trachea,  and  partly  by  enabling  us  to  regulate  and  vary  the 
opening  of  the  glottis  whilst  we  preserve  the  tension  of  the  vocal 
chords. 

768.  Such  being  the  mode  in  which  vocal  sounds  are  produced 
in  the  larynx,  the  next  step  in  the  inquiry  will  relate  to  modifica- 
tions they  receive  from  the  shape  of  the  cavities  of  the  pharynx 
and  mouth,  through  which  the  expired  air  has  yet  to  pass.  When 
thus  modified  they  become  not  merely  vocal,  but  articulate 
sounds,  and  constitute  the  elements  of  speech. 

769.  This  branch  of  the  subject  has  been  ably  investigated  by 
Sir  Charles  Bell,*  who  has  traced  the  influence  which  the  changes 
produced  by  the  muscular  actions  of  the  tongue  and  fauces,  on 
the  shape  of  the  cavities  of  the  mouth  and  pharynx,  have  on  the 
resulting  articulate  sounds.  He  has  examined  the  succession  of 
actions  which  must  be  performed  before  a  word  can  be  uttered, 
and  which  he  finds  to  consist  in  the  compression  of  the  thorax, 

*  Philosophical  Transactions  for  1832,  p.  299. 


324  '  SENSORIAL    FUNCTIONS. 

as  well  as  the  adjustment  of  the  glottis,  the  elevation  and  depres- 
sion of  the  larynx,  and  the  contraction  of  the  pharynx. 

770.  The  elementary  articulate  sounds  of  a  langua'ge  consist 
of  vowels  and  consonants.  Vowels  are  continued  sounds,  pro- 
duced when  the  passage  of  the  air  through  the  fauces  is  uninter- 
rupted, the  fauces  being  only  more  or  less  narrowed.  Each 
vowel  requires  a  different  elevation  of  the  tongue  or  contraction 
of  the  lips.  Thus  the  sound  of  the  broadest  pronunciation  of  the 
letter  a,  which  occurs  in  the  word  awe,  results  from  the  lowest 
position  of  the  tongue,  giving  its  greatest  depth  to  the  cavity  of 
the  mouth.  The  ordinary  sound  of  a,  as  in  the  word  age,  is  pro- 
duced by  a  certain  elevation  of  the  tongue,  reducing  considerably 
the  capacity  of  the  mouth.  The  vowel  e,  pronounced  as  in  eve, 
is  sounded  by  raising  the  tongue  still  more,  so  as  to  leave  a  more 
contracted  channel  for  the  exit  of  the  air.  The  positions  for  o 
and  00,  are  obtained  by  placing  the  fauces  in  the  position  first 
described,  namely,  that  for  au,  and  then  approximating  the  lips. 

771.  The  pronunciation  of  consonants  is  effected  by  interrup- 
tions to  the  passage  of  the  air  in  some  part  of  the  cavity  of  the 
mouth,  by  various  motions  of  the  tongue  and  lips,  which,  when 
applied  to  the  palate  of  the  teeth,  narrow  or  close  the  channel  for 
its  exit. 

772.  The  following  experiment  is  mentioned  by  Mr.  Mayo* 
as  having  been  made  by  M.  Deleau,  demonstrating  that  the 
articulation  of  vocal  sounds  takes  place  in  the  fauces.  He  intro- 
duced through  the  nostrils  into  the  pharynx  a  flexible  tube,  and, 
by  means  of  a  gum  bottle,  impelled  air  through  it  into  the  fauces ; 
then  closing  the  larynx  he  threw  the  fauces  into  the  different 
positions  requisite  for  producing  articulate  sounds,  when  the  air 
impelled  from  the  gum  bottle  became  an  audible  whisper.  Dr. 
Bennati  repeated  this  experiment,  allowing  at  the  same  time 
laryngeal  sounds  to  pass  into  the  fauces,  when  each  articulated 
letter  was  heard  double,  in  a  voice  at  once,  and  in  a  whisper. 

773.  Consonantal  sounds  may  be  divided,  first,  into  aspirates 
and  sonants,  or,  secondly,  into  continuous  and  explosive. 

114:.  The  aspirates  are  those  which  may  be  rendered  audible 
without  a  vocal  sound,  as  in  the  case  with  p,  t,  k,  h,f,  th,  s,  and 
sh.  The  sonants  are  those  which,  without  any  appreciable  dif- 
ference in  the  shape  of  the  fauces  from  the  form  required  for  the 
pronunciation  of  the  preceding  to  which  they  are  allied,  are  not 
heard  without  a  vowel  sound,  either  previously  uttered,  as  in  b, 
d,  g,  V,  z,  and  /,  or  subsequently,  as  in  g,  or  in  conjunction  with 
it,  as  in  r. 

775.  Continuous  consonants  are  pronounced  when  the  vocal- 
ized air  passes  through  some  part  of  the  organ,  previously  ren- 

*  Outlines  of  Human  Physiology,  p.  354. 


THE    VOICE.  325 

dered  very  narrow.  Explosive  consonants  are  those  which  are 
produced  by  the  interruption  to  the  current  of  air  occasioned  by 
the  entire  closing  of  the  passage,  and  its  being  allowed  to  burst 
out  with  some  force  by  the  sudden  opening  of  the  same  passage. 

776.  The  nasal  consonants,  w,  n,  and^,  are  distinguished  from 
the  rest  by  the  peculiur  character  of  their  articulation  arising 
from  the  breath  being  allowed  to  pass  through  the  nostrils  ;  whilst 
in  the  pronunciation  of  the  others,  the  soft  palate  being  raised 
closes  the  posterior  nostrils,  and  prevents  the  sound  from  diffusing 
itself  in  that  direction. 

777.  We  refrain  from  entering  into  any  further  details  with 
regard  to  the  position  of  the  fauces,  tongue,  and  lips,  in  the  pronun- 
ciation of  the  different  consonants,  having  already  treated  of  this 
Subject  at  some  length.* 

778.  The  low  pitch  of  the  voices  of  men  compared  with  those 
of  wom.en  and  boys,  arises  both  from  the  greater  general  size  of 
the  larynx,  and  also  the  greater  length  of  the  chordse  vocales, 
which  has  been  found  to  measure  nearly  double  that  of  the  latter. 
In  attempting  to  utter  high  notes,  voices  naturally  grave,  assume 
the  character  of  the  falsetto.  This,  Mr.  Willis  supposes,  may 
result  from  the  shortening  of  the  vocal  chords ;  but  Mr.  Wheat- 
stone  is  disposed  to  ascribe  it  to  the  tension  given  to  the  windpipe 
being  such  as  to  reinforce  the  laryngeal  sounds  by  subdivisions. 

779.  Some  curious  observations  on  the  mechanism  of  the  voice 
during  singing  have  lately  been  given  by  Dr.  Bennati,t  who  states, 
that  the  compass  of  his  own  voice  extends  to  three  octaves.  He 
concludes  from  his  inquiries,  that  it  is  not  merely  the  muscles  of 
the  larynx  which  modulate  the  sounds,  but  those  also  of  the  os 
hyoides,  and  the  other  neighbouring  parts.  He  mentions  that,  on 
removing  part  of  the  tonsils,  the  operation  was  followed  by  the 
raising  of  the  voice  half  an  octave,  without  ahering  its  compass. 
Mr.  Mayo  supposes  this  effect  to  result  from  the  cicatrix  stretch- 
ing the  mucous  membrane  of  the  larynx,  and  thus  giving  increased 
tension  to  its  inner  surface.^ 

*  Art,  Deaf  and  Dumb — Encyclopeedia  Britannica,  7th  edit.  See  also 
Haller's  Elementa  de  Physiologiae,  ix.  4 ;  Dr.  Young's  Lectures,  ii.  276  ; 
and  the  work  of  Mr.  Mayo,  already  quoted. 

f  Annales  des  Sciences  Naturelles,  xxiii.  32.    « 

X  [See  an  elaborate  article  on  the  voice  in  its  various  manifestations,  in 
Dunglison's  Physiology,  i.  395.] 


28 


326  REPRODUCTIVE    FUNCTIONS. 


CHAPTER    XIX. 

GENERATION. 

Sect.  L — General  Views. 

•780.  As  far  as  we  are  permitted  to  scan  the  designs  of  the 
Almighty  Creator  in  the  formation  of  organized  beings,  they  ap- 
pear destined  to  a  mode  of  existence  characterized  by  perpetual 
mutation.  Their  Hving  state  is  made  to  consist  of  a  perpetual 
series  of  actions  and  reactions,  in  which  nothing  is  intended  to 
be  permanent,  not  even  the  materials  of  which  the  combinations 
constitute  the  substance  and  organs  of  the  body.  All  is  subject 
to  displacement,  alteration,  renewal,  and  renovation,  during  a 
certain  definite  period,  which  varies  in  each  species,  according 
to  the  primordial  law  of  its  constitution ;  and  all  must  bend,  when 
that  period  is  exceeded,  to  the  imperative  law  of  mortality,  to 
which  every  individual  endowed  with  life  is  subjected. 

781.  But  the  same  counsels  which  prescribed  these  limits,  and 
decreed  the  extinction  of  life,  and  the  dissolution  of  the  frame  in 
which  it  had  resided,  have  providently  ordained  most  ample 
means  for  the  continuance  of  the  race,  and  the  indefinite  multi- 
plication of  its  numbers.  Individuals  perish,  but  the  species  is 
preserved  in  endless  perpetuity  by  means  of  Generation  ;  a 
function  of  paramount  importance  in  the  economy  of  nature,  and 
for  which  the  most  ample  provision  has  been  made,  and  the 
greatest  solicitude  manifested  to  secure  the  accomplishment  of 
its  pui'poses.  Nutrition  and  generation,  indeed,  constitute  the 
only  functions  which  can  be  said  to  be  universally  exercised  by 
all  organized  beings,  whether  belonging  to  the  vegetable  or  the 
animal  kingdom,  or  whatever  rank,  from  the  lowest  to  the  highest, 
they  may  occupy  in  the  scale  of  nature. 

782.  But  although  the  purpose  is  thus  manifest,  and  the  provi- 
sions for  its  execution  thus  eflfective  and  even  exuberant,  the 
immediate  agency  by  which  one  living  being  is  rendered  capable 
of  giving  rise  to  another  sim.ilar  to  itself,  is  enveloped  in  the  most 
profound  and  most  hopeless  obscurity.  No  means  within  the 
compass  of  our  understanding,  no  combination  of  the  powers  of 
matter  which  we  can  possibly  conceive,  no  process  of  which  the 
utmost  stretch  of  human  imagination  can  give  us  the  most  remote 
idea,  has  ever  made  the  least  approach  towards  the  solution  of 
this  most  inexplicable  of  all  enigmas, — the  production,  nay,  the 
apparent  creation,  of  a  living  plant  or  animal  by  powers  inherent 


GENERATION.  327 

in  the  organization  of  a  similar  being.  We  must  content  our- 
selves, in  studying  this  inscrutable  mystery,  to  observe  and 
generalize  the  phenomena,  in  silent  astonishment  at  the  marvel- 
lous manifestation  of  design  and  of  povi^er  exhibited  in  this  depart- 
ment of  the  vv^onderful  works  of  the  Almighty. 

783.  Various  plans  of  reproduction  are  exhibited  in  the  differ- 
ent classes  of  animals,  but  they  are  all  reducible  to  three  general 
heads,  which  may  be  designated  by  the  titles  o(  fissiparous,  gem- 
mijyarous,  and  sexual  reproduction.  Many  physiologists,  however, 
have  been  disposed  to  admit  the  existence  of  a  fourth  mode  of 
reproduction,  which  they  have  termed  spontaneous,  or  equivocfd 
generation.  It  is  contended  by  the  advocates  of  this  hypothesis, 
that  in  many  of  the  lower  tribes,  instances  occur  of  the  formation 
of  animals  without  the  intervention  of  any  parents,  and  produced 
by  the  spontaneous  union  of  certain  elements,  which  might  for- 
tuitously be  found  in  juxtaposition,  in  collections  of  the  decom- 
posing materials  of  other  organized  structures,  after  the  extinction 
of  their  life.  Although  this  opinion  was  at  one  period  the  gene- 
rally prevailing  doctrine,  it  is  now,  in  consequence  of  the  more 
extensive  knowledge,  which  has  been  obtained  of  the  procedure 
of  nature  in  the  multiplication  of  animals,  very  generally  exploded. 
The  principal  arguments  in  its  favour  were,  in  the  first  place, 
those  drawn  from  the  existence  of  intestinal  worms,  and  other 
parasitic  entozoa,  in  the  bodies  of  animals,  the  germs  of  which 
appear  neither  to  be  introduced  into  the  system  from  without,  nor 
to  have  any  assignable  origin  from  within ;  secondly,  those 
derived  from  the  rapid  appearance  of  infusory  animalcules  in  all 
infusions  of  decaying  animal  or  vegetable  matter  that  are  exposed 
for  a  short  time  to  the  air.  But  the  analogy  of  every  other  de- 
partment of  the  animal  and  vegetable  kingdom  is  directly  opposed 
to  the  supposition  that  any  living  being  can  arise,  unless  it  has 
originally  sprung  from  an  individual  of  the  same  species  as  itself, 
and  of  which  it  once  formed  a  part.  The  difficulty  which  the 
hypothesis  of  the  spontaneous  production  of  infusory  animalcules 
professes  to  remove,  consists  in  our  inability  to  trace  the  pre- 
existence  of  the  germs  in  the  fluid  where  these  animalcules  are 
found  to  arise,  and  to  follow  the  operations  of  nature  in  these 
regions  of  infinite  minuteness.  But  the  recent  discoveries  of 
Ehrenberg  relative  to  the  complete  organization  of  these  beings, 
in  which  he  in  many  instances  detected  the  presence  of  genera- 
tive organs,  has  very  much  diminished  the  difficulty  of  conceiving 
the  possibility  of  their  ova,  so  minute  as  to  be  wholly  impercep- 
tible, existing  in  great  numbers  in  the  fluid,  or  even  in  the 
atmosphere,  and  giving  rise  to  all  the  observed  phenomena.* 

*  See  Bridgewater  Treatise,  on  Animal  and  Vegetable  Physiology,  vol.  ii, 
p.  591,  note.     [Amer.  edit.  ii.  415.] 


328  REPRODUCTIVE    TUNCTIONS. 

784.  Fissiparous  generation,  the  simplest  of  all  possible  modes 
in  which  the  species  can  be  multiplied,  consists  in  the  spontane- 
ous and  gradual  division  of  the  body  of  an  individual  animal  into 
two  or  more  parts,  which,  when  the  division  is  completed,  sepa- 
rate, and  each  soon  assumes  the  form,  and  grows  to  the  size  of 
the  parent,  and  becomes  capable  of  performing  all  the  functions 
which  originally  belonged  to  the  undivided  animkl.  The  most 
common  form  of  this  mode  of  generation  is  met  with  in  some  of 
the  simpler  of  the  infusoria,  as  the  monas,  the  gonium,  the  cycli- 
dium,  the  vorticellse,  and  the  volvox.  In  the  instance  of  the 
volvox,  however,  we  find  an  approach  to  the  next  order ;  for  the 
young  are  seen  forming  within  the  body  of  the  parent,  which  is, 
in  course  of  time,  reduced  to  a  mere  membranous  vesicle,  and 
then  bursts,  and  is  torn  into  shreds,  setting  free  the  enclosed 
young,  each  of  which  immediately  begins  to  execute  its  indepen- 
dent movements  in  the  fluid. 

785.  Gemmiparous  generation  occurs  when  a  new  individual 
grows  from  the  parent  as  a  bud  or  sprout;  at  first  exhibiting  but 
little  resemblance  in  shape  or  structure  to  the  parent  animal,  but 
gradually  assuming  that  form  whilst  still  adhering  to  it,  and 
being  afterwards  detached  to  commence  an  independent  exist- 
ence. Numerous  examples  occur  of  this  mode  of  reproduction 
amongst  the  lower  orders  of  zoophytes,  such  as  animals  belong- 
ing to  the  tribe  of  polypi,  of  which  the  hydra  viridis,  rendered  cele- 
brated by  the  researches  of  Ti'embley,  may  be  taken  as  the  type. 
Sometimes,  as  happens  in  the  sponge,  the  actinia,  and  some  of 
the  lower  orders  of  mollusca,  the  young  are  formed  from  small 
detached  masses  after  they  are  separated  from  the  body  of  the 
parent.  These  bodies,  which  are  called  spores,  or  gemm.uhs,  are 
generally  of  a  rounded  form  and  homogeneous  structure ;  and 
the  whole  substance  of  which  they  are  composed  is  converted 
during  their  development  into  the  new  animal.  Hence  they  may 
be  regarded  as  buds  formed  in  the  parent  body,  but  detached 
from  it  before  the  evolution  of  the  new  animal  begins.  In  some 
species  these  gemmules^  are  formed  in  all  parts  of  the  body  indis- 
criminately ;  but  in  most  others  there  is  a  particular  generative 
organ  provided  for  their  formation. 

786.  In  by  far  the  greater  number  of  organized  beings  no 
reproduction  takes  place  except  by  the  co-operation  of  two  kinds 
of  generative  organs ;  laying  the  foundation  of  the  distinctions 
of  sex,  and  constituting  sexual  generation.  As  characterising 
the  female,  there  is,  in  the  first  place,  an  organ,  termed  the  ovary, 
of  which  the  olRce  is  to  form  the  ova,  or  eggs.  These  are 
organized  bodies  of  a  determinate  shape,  within  which  we  first 
find  the  earHest  rudiments,  or  germ,  of  the  future  animal  contained 
in  a  fluid,  which  is  itself  enclosed  in  a  vesicle.  But  the  ovum, 
or,  more  properly  speaking,  the  ovulum,  thus  formed  exclusively 


GENERATION.  329 

by  the  female  organs,  never  advances  in  its  development  beyond 
this  stage,  and  can  never  ffive  rise  to  a  new  animal,  unless  it 

•  •  •       L  L 

receive  a  certain  vivifying  impression  given  to  it  by  the  contact 
of  a  peculiar  fluid,  denominated  the  semen,  which  has  been  pre- 
pared by  a  totally  distinct  apparatus,  constituting  the  male 
organs. 

787.  The  nature  of  the  impression  thus  made  by  the  seminal 
fluid  on  the  ovulum,  or  immature  ovum,  and  which  constitutes  its 
fecundation,  and  awakening  in  it  a  power  of  reproduction,  which 
*had  before  remained  dormant,  is  wholly  unknown ;  nor  is  it 
accompanied  with  any  immediate  alteration  in  its  appearance  or 
structure.  None  of  the  parts  of  the  new  animal  can  yet  be 
discerned  in  the  fluid  contents  of  the  ovulum,  the  great  mass  of 
which  consists  of  a  fluid  holding  in  suspension  granules  of  albumi- 
nous or  oily  matter;  and  a  certain  time  must  elapse,  even  in  the 
most  favourable  circumstances,  before  the  formative  process  exhi- 
bits its  effects.  The  form  of  the  egg  is  given  by  the  external 
coverings,  and  there  is  in  every  egg  a  determinate  part,  at  which 
the  minute  rudimental  germ  of  the  embryo  is  first  visible.  It  is 
to  this  germ  that  the  power  of  independent  life  and  development 
appears  more  immediately  to  belong,  the  granular  fluid  serving 
only  as  nutriment  laid  up  in  store  for  the  supply  of  materials  for 
growth. 

788.  Thus  the  processes  essential  to  sexual  reproduction  consist, 
first,  in  the  formation  of  an  ovulum  by  the  female  organs ;  second, 
in  the  secretion  of  the  seminal  fluid  by  the  male  apparatus;  third, 
in  the  application  of  the  seminal  fluid  to  the  ovulum  so  as  to  confer 
on  it  fecundity. 

789.  The  mode  in  which  this  application  is  made  differs  accor- 
ding as  the  male  and  female  organs  are  both  contained  in  the  system 
of  the  same  individual,  (as  occurs  in  monacious  plants  and  herma- 
phrodite animals,)  or  exist  separately  in  different  individuals  (as 
in  dioecious  plants,  and  all  the  higher  classes  of  animals).  In  the 
former  case,  self-impregnation  may  take  place,  either  by  the 
required  seminal  access  being  effected  internally  in  each  individual 
independently  of  any  other;  or,  in  other  cases,  by  the  concurrence 
of  two  individuals  in  sexual  union  which  reciprocally  impregnate 
one  another  (as  is  exempHfied  in  the  leech,  the  earth-worm,  and 
the  snail).  In  the  second  division,  where  the  male,  or  fertilizing 
organs,  are  possessed  exclusively  by  one  individual,  and  the  female 
organs,  or  those  producing  the  germ,  by  another,  impregnation  of 
the  ova  may  take  place  either  after  their  exclusion  from  the  body 
of  the  female  parent,  by  their  contact  with  the  male  semen  ejected 
on  them  when  thus  excluded  (as  happens  in  the  case  of  fishes  and. 
batrachian  reptiles),  or  within  the  body  of  the  female  ;  for  which 
latter  purpose,  a  new  function,  that  of  copulation,  becomes  neces- 
sary.    This  last  mode  of  procedure  is  had  recourse  to  by  nature 

28* 


330  ,  feEPRODUCTIYE    FUNCTIONS. 

in  by  far  the  largest  portion  of  the  animal  kingdom,  including  all 
the  tribes  of  insects,  nearly  all  the  mollusca,  and  all  warm-blooded 
vertebrated  animals. 

■  790.  All  the  subsequent  phenomena  relate  to  the  development 
of  the  embryo  thus  brought  into  existence;  to  the  supply  of  nourish- 
ment for  its  growth;  and  to  the  advantages  of  situation,  of  warmth, 
and  of -protection,  which  are  necessary  for  the  favourable  proce- 
dure of  the  vital  powers  in  the  progress  of  this  development. 

791.  Various  plans  are  resorted  to  for  conducting  these  pro- 
cesses of  development  of  the  fecundated  ovum.  In  that  which  is 
termed  oviparous  generation,  the  ovum,  during  its  passage  through 
the  oviduct,  receives  the  addition  of  a  considerable  quantity  of 
nutritious  matter,  sufficient  for  the  supply  of  all  the  materials 

.  requisite  for  its  growth,  until  the  'period  when  it  is  capable  of 
procuring  food  for  itself;  and  it  also  acquires  a  capsule,  or  sub- 
stantial covering,  frequently  of  a  calcareous  nature,  fitted  for  its 
protection  under  the  circumstances  in  which  it  is  to  be  placed. 
When  thus  formed  it  constitutes  an  egg,  or-eonrplete  ovum ;  and 
in  this  form  it  is  either  excluded  from  the  body  of  the  female  parent, 
and  hatched,  if  already  fecundated,  by  the  influence  of  external 
warmth;  or  if  not  previously  fecundated,  this  change  is  accom- 
plished by  the  seminal  fluid  of  the  male  being  shed  upon  it.  The 
former  case,  which  implies  sexual  congress,  is  exemplified  in  all 
insects  and  birds :  the  latter,  which  requires  no  such  congress, 
obtains  in  fishes,  and  many  of  the  reptilia.  Both  are  compre- 
hended under  the  term  oviparous  animals. 

792.  In  a  few  instances  the  eggs,  previously  fecundated  within 
the  body  of  the  female,  instead  of  being  expelled,  remain  in  the 
oviducts  until  they  are  spontaneously  hatched,  and  the  young  are 
then  brought  forth  alive.  This  phenomenon,  which  is  exhibited 
by  many  cartilaginous,  and  a  few  osseous  fishes,  by  several  rep- 
tiles, and  by  some  gasteropodous  mollusca,  insects,  annehda,  and 
entozoa,  has  been  called  ova-viviparous  generation. 

793.  In  mammiferous  generation,  on  the  other  hand,  the  ovum, 
which  is  not  perfected  in  the  same  degree  as  in  the  two  former 
cases,  remains  within  the  female,  and  is  attached,  by  the  medium 
of  a  substance  called  the  placenta,  to  the  inner  surface  of  an 
organ  termed  the  uterus,  where  it  receives  nourishment  from  the 
maternal  system,  and  where  it  remains  until  it  is  capable  of  inde- 
pendent life,  and  it  is  then  brought  forth.  This  retention  during 
growth  in  the  uterus  is  termed  utero-gestation,  and  its  subsequent 
exclusion  is  termed  parturition.  The  young  of  mammaha  after 
birth,  although  they  cease  to  be  organically  connected  with  the 
mother,  continue  to  derive  from  her  a  certain  quantity  of  suste- 
nance in  the  form  of  milk,  which  is  a  secretion  from  certain 
glands  termed  mammce,  the  possession  of  which  is  the  character- 
istic feature  of  this  class  of  animals.    An  exception  occurs  in  the 


GENERATION. 


331 


case  of  marsupiate  animals,  in  whom  the  young  leaves  the  uterus 
at  a  very  early  period  of  its  formation,  while  it  is  yet  of  a  very 
small  size,  and  its  organs  are  comparatively  imperfectly  formed. 
On  being  born  it  is  introduced  by  the  mother  into  a  pouch, 
termed  the  marsupium,  formed  by  a  folding  of  the  integuments  of 
the  lower  part  of  the  belly ;  and  a  shor^  time  after  it  has  been 
deposited  there,  it  is  found  attached  by  its  mouth  to  one  of  the 
nipples  of  the  mammas,  which  are  concealed  within  the  marsu- 
pium, and  there  receives  its  nourishment  until  it  has  acquired 
sufficient  size  and  strength  to  quit  its  habitation.  Monotrematous 
generation,  which  is  peculiar  to  the  ornithorynchus  and  echidna, 
is  not  yet  perfectly  understood.  The  generative  organs,  and  the 
ova  within  the  ovaries,  in  these  animals,  partake  in  a  great  de- 
'  gree  of  the  oviparous  type ;  but  they  are  also  combined  with  the 
presence  of  mammary  glands,  which  perform  the  office  of  lacta- 
tion, as  in  the  strictly  viviparous  class  of  animals. 

794.  The  following  table,  w^hich  is  nearly  that  given  by  Dr. 
Allen  Thomson,*  exhibits  a  synoptical  view  of  the  various  forms 
of  the  reproductive  process  occurring  in  different  classes  of 
animals : — 


OS  ^ 


fFissiparous, 


Gemmiparous,    ^ 


Monoecious, 
or 


C    A.  The  parent  splits  into  two  or  more  parts, 
I  each  part  becoming  a  new  animal. 
I  1.  By  transverse  fissure. 

-<[  2.  By  longitudinal  fissure. 

13.  Irregularly. 
B.  The  parent  bursts,  and  the  included  young 
l^are  discharged. 

f    A.  Buds  sprouting  from  the  parent  stock. 
B.   Gemmse,  or  Sporules,  formed — 
1.  In  all  the 'parts  of  the  body. 
(_         2.  In  one  part  only. 

r    Both  sexual  organs  contained  in  the  same  in- 
)  dividual. 


< 


,S     Hermaphrodite, 


^M 


1.  By  self-impregnation. 
i_        2.   By  mutual  impregnation. 
f    A.  Oviparous ,-  eggs  laid,  and  afterwards  hatched. 

II.  Eggs  fecundated  externally. 
2.  Eggs  fecundated  internally. 
1^     Bicecious,  .     <(       B.    Ovo-viviparous ,-    eggs   hatched   within   the 

I  maternal  body. 
Mammiferous ;  the  parent  suckling  the  young 
Lby  mammae. 

1.  Monotrematous. 

2.  Marsupial. 

3.  Placental,  or  strictly  viviparous. 

795.  A  wide  range  of  inquiry  is  here  opened  to  us,  compre- 
hending, if  we  were  to  include  in  its  field  the  whole  of  the  animal 

*  Cyclopaedia  of  Anatomy  and  Physiology,  by  Dr.  Todd,  article  Genera- 
tion, p.  438,  to  which  article  we  are  largely  indebted  in  the  compilation  of 
this  chapter. 


332  REPRODUCTIVE    FUNCTIONS. 

kingdom,  an  immense  multitude  of  facts,  to  the  complete  study 
of  which  the  labours  of  a  whole  life  would  be  inadequate.  We 
are,  however,  to  confine  ourselves,  at  present,  to  the  view  of 
human  physiology;  but  even  here  the  great  extent  of  the  subject 
obliges  us  to  reduce  within  a  narrow  compass  the  account  we 
have  to  give  of  this  important  and  interesting  department  of  the 
science.  For  this  purpose,  after  a  short  description  of  the  cir- 
cumstances relating  to  the  unimpregnated  ovum,  we  shall  proceed 
to  the  physiology  of  the  male  and  female  systems  respectively, 
bringing  its  history  to  the  period  of  the  fecundation  of  the  ovum. 
This  latter  subject  will  lead  us  to  consider  some  of  the  most 
celebrated  theories  of  generation ;  after  which  we  shall  briefly 
consider  the  phenomena  of  utero-gestation  and  parturition,  which 
are  functions  belonging  exclusively  to  the  female  parent,  but 
which  accompany  and  are  accommodated  to  the  successive 
changes  attending  the  development  of  the  foetus.  Of  these  latter 
changes,  relating  to  the  system  of  the  new  individual,  it  will  be 
more  convenient  to  give  the  history  separately. 


Sect.  II. — Unimpregnated  Ovum. 

796.  Much  difficulty  is  necessarily  experienced  in  obtaining 
direct  evidence  of  the  early  changes  occurring  in  the  iprocess  of 
human  generation,  from  the  scanty  opportunities  allowed  us  of 
direct  observation  of  those  changes,  and  from  our  being  precluded 
from  resorting  to  the  most  instructive  fountain  of  knowledge, 
namely,  experimental  research.  Whilst,  therefore,  we  obtain 
occasional  views  of  the  actual  phenomena  which  occur  in  man, 
we  must  content  ourselves  with  filling  up  the  chasms  in  the  con- 
tinuous history  of  his  generation,  by  the  observation  of  those 
which  are  presented  in  ^the  lower  animals  that  most  resemble 
him  in  the  mode  in  which  this  function  is  conducted,  and  by 
remoter  analogies  derived  from  other  classes. 

797.  It  is  well  estabhshed,  from  these  combined  sources  of 
information,  that  the  essential  part  of  the,  female  system  con- 
cerned in  generation  is  the  ovary,  or  ovarium,  of  which  there  is 
one,  situate  on  each  side,  in  the  cavity  of  the  pelvis.  The  ovaries 
are  small  capsular  bodies,  of  an  oblong,  or  oval,  and  somewhat 
flattened  shape,  which  are  enveloped  in  the  fold  of  the  peritoneum, 
forming  the  broad  ligaments  of  the  uterus.  They  are  composed 
of  a  white  and  loose  cellular  texture,  in  which  we  discover 
several  minute  vesicles,  or  cysts,  filled  with  a  transparent  fluid, 
and  termed,  from  the  name  of  De  Graaf,  who  first  observed  them, 
the  Graafian  vesicles.  Their  number  is  generally  from  fifteen 
to  twenty  in  each  ovarium,  and  they  vary  in  size,  the  largest 
being  about  one-third  of  an  inch  in  its  longest  diameter.     The 


UNIMPREGNATED    OVUM.  333 

flui^  which  is  contained  in  these  vesicles  is  slightly  viscid  and 
albuminous,  inclining  to  a  yellow  colour  in  the  most  turgid  vesi- 
cles, containing  numerous  granules  of  an  irregular  shape,  and  a 
few  globules  of  oil,  but  being  otherwise  pellucid, 

790.  Besides  the  peritoneal  covering  already  described,  the 
ovarium  has  a  cellular  coat  proper  to  itself  Each  of  the  Graafian 
vesicles  has  a  double  investment ;  the  outer  coat  consisting  of  a 
close  filamentous  texture ;  and  the  internal  layer  being  thicker, 
softer,  and  more  opaque  than  the  outer,  from  which  it  is  readily 
separable  after  maceration,  and  having  a  slightly  villous  inner 
surface.  The  membrane  immediately  containing  the  granular 
fluid  above  described,  also  exhibits  the  appearance  of  being 
studded  with  granules,  and  is  on  that  account  styled  the  mem- 
brana  granulosa.  Within  the  granular  fluid  is -found  a  body, 
composed  of  closely  coherent  granules,  which  has  been  deno- 
minated by  its  discoverer,  Baer,  the  discus  proUgerus,  and  which 
he  represented  as  having  a  flattened  or  discoid  form,  and  as 
forming  the  bed  in  which  is  placed  the  minute  vesicle  of  the 
ovulum,  or  germ  of  the  unimpregnated  ovum.  The  later  re- 
searches of  Dr.  Martin  Barry,  of  which  he  has  given  an  account 
in  a  paper  communicated  to  the  Royal  Society  of  London,  have 
thrown  further  light  on  this  branch  of  Zoology.  The  following 
is  a  summary  of  the  principal  conclusions  at  which  he  has  arrived 
on  this  subject. 

800.  The  ovulum  of  all  vertebrated  animals,  and  of  many  of 
the  invertebrata  also,  is  contained  in  a  vesicle,  called  by  some 
authors  the  chorion,  but  which  Dr.  Barry  thinks  it  desirable, 
wherever  found,  to  call  an  ovisac.  He  considers  the  Graafian 
vesicle  of  the  mammalia,  and  aleo  the  capsule,  or  calyx  of  ovi- 
parous vertebrata,  as  an  ovisac  which  has  acquired  a  covering ; 
which  covering  is  the  "  couche  externe^^  of  the  "  capsule  cle  la 
vesicule  de  Graaf"  of  Baer.  The  perfect  Graafian  vesicle  of  the 
mammalia  has  been  shown  by  preceding  physiologists  to  be  ana- 
logous to  the  perfect  capsula,  or  calyx  of  the  bird ;  but  the  ana- 
logy is  found  by  Dr.  Barry  to  be  much  more  remarkable  between 
the  ovisacs  of  these  two  classes  of  animals,  before  these  additional 
coverings  have  been  acquired ;  and  this  analogy  may  also  be 
extended  to  those  of  amphibia  and  fishes,  so  that,  in  fact,  the 
surfaces  of  all  the  vertebrata  are  in  their  original  structure 
essentially  the  same  ;  a  conclusion  which  Dr.  Barry  is  disposed 
to  extend  also  to  the  ovisacs  of  many  of  the  invertebrata. 

801.  The  ovisac,  being  originally  an  independent  structure, 
can  be  better  studied  in  this  state,  than  at  a  later  period,  when 
it  has  become  the  lining  membrane  of  the  Graafian  vesicle  or 
calyx.  Thus,  while  the  perfect  Graafian  vesicle  of  the  mammal, 
and  the  perfect  capsule  of  the  bird,  are  obviously  corresponding 
structures,  there  yet  exists  this  difference,  that  there  is  a  space, 


334  REPRODUCTIVE    FUNCTIONS. 

filled  with  a  large  quantity  of  fluid  in  the  former,  not  present  in 
the  latter;  a  difference  which  does  not  exist  in  the  early  stages 
of  formation,  when  ovisacs  in  general  appear  in  this  respect  to 
be  essentially  the  same.  The  structure  of  the  ovisac  may  be 
examined,  in  some  mammalia,  when  it  does  not  exceed  in  length 
the  600th,  or  even  1200th  part  of  an  inch  ;  so  that  in  the  latter 
case,*^a  cubic  inch  would  contain  1,728,000,000. 

802,  The  ovisac  of  the  vertebrata,  and  perhaps  of  other  ani- 
mals, is  at  first  of  an  elliptical  form.  In  the  mammaha  and  birds, 
myriads  of  ovisacs  and  ovula  are  formed,  which  never  reach 
maturity.  Many  of  these  are  formed  in  the  substance  of  the 
proper  membrane  of  larger  ovisacs,  and  are  therefore  termed  by 
Dr.  Barry  parasitic  ovisacs. 

'■■  803.  The  ovisac  is  formed  in  a  cavity  proper  to  itself,  with 
which  .it  does  not  appear  to  have  any  organic  connexion.  The 
granules  found  in  the  fluid  of  the  ovisac  are  very  characteristic 
in  their  appearance,  and  imply  the  presence  of  albumen  in  a  con- 
centrated form.  A  stratum  of  these  granules,  found  on  the  in- 
ternal surface  of  the  proper  membrane  of  the  ovisac,  constitutes, 
as  Baer  remarks,  a  distinct  membrane.  But  the  mass  of  granules 
described  by  that  anatomist  as  being  discoid,  is  believed  by  Dr. 
Barry  to  be  of  a  spherical  form.  This  latter  observer  finds  that 
the  ovulum  of  vertebrated  animals  is,  when  first  formed,  situated 
in  the  centre  of  the  fluid  of  the  ovisac,  and  more  or  less  obviously 
held  there  by  a  flake  of  granules ;  and  has  at  first  no  proper 
envelope  of  granules.  In  the  mammalia,  there  forms  around  the 
ovulum  a  granulous  covering  of  a  spherical  form,  which  Dr. 
Barry  terms  the  tunica  granulosa ;  but  it  has  no  discoid  mass  of 
granules  proper  to  it.  At  a  certain  period,  the  ovulum  of  the 
mammalia  passes  from  the  centre  of  the  ovum  to  the  periphery ; 
and  there,  while  invested  by  its  granulous  tunic,  it  penetrates  the 
membrana  granulosa,  leaving  behind  it  a  flake  of  granules.  Here 
it  lies  quite  in  contact  with  the  proper  membrane  of  the  ovisac, 
is  more  or  less  imbedded  in  the  membrana  granulosa,  and  is 
supported  behind  by  a  mass  of  granules,  sometimes  presenting 
the  appearance  denominated  by  Baer  the  cumulus.  But  this 
cumulus  does  not  belong  to  the  proper  granulous  covering,  or 
tnnica  granulosa,  of  the  ovulum ;  for  it  may  in  some  animals  be 
separated  from  this  covering,  in  the  form  of  what  Dr.  Barry  calls 
the  petasiolus  granulosus. 

804.  After  the  ovulum  has  reached  the  periphery,  its  tunica 
granulosa  may,  at  least  in  some  animals,  by  contact  with  the 
membrane  of  the  ovisac,  become  attenuated,  or  may  even  disap- 
pear at  one  side ;  which  circumstance,  together  with  the  great 
transparency  of  this  tunic,  may  have  been  the  cause  of  Baer's 
assigning  to  it  a  discoid  form.  This  approximation  of  the  ovulum 
to  the  exterior  surface  of  the  ovisac,  is  doubtless  for  th6  purpose 


THE    MALE    SYSTEM.  33& 

of  exposing  it  to  the  action  of  the  fecundating  seminal  fluid,  which 
reaches  it  while  it  is  in  this  situation,  and  still  in  the  ovary.  The 
next  step  being  now  the  application  of  this  fluid,  we  are  brought 
to  the  next  stage  of  our  inquiry,  namely,  into  the  series  of  appa- 
ratus and  of  functions  provided  for  the  preparation  of  the  semen,, 
its  introduction  into  the  female  organs,  and  its  transmission  to- 
the  surface  of  the  ovulum. 


Sect.  III. — IVie  Male  System, 

805.  The  preparation  of  the  seminal  fluid  is  the  office  of  the 
two  glandular  bodies  called  the  testicles  or  testes.  They  are  sus- 
pended in  a  portion  of  common  integument  having  the  form  of 
sac,  termed  the  scrotum^  by  a  round  band,  called  the  spermatic 
cord,  which  pursues  a  very  serpentine  course ;  a  plexus  of  veins, 
the  assemblage  of  which  has  received  the  name  ot  corpus  pampi- 
neforme,  consisting  of  the  spermatic  artery,  a  plexus  of  absorb- 
ents, a  plexus  of  nerves ;  and  lastly,  the  vas  deferens,  or  excre- 
tory duct ;  and  they  are  further  supported  by  a  sub-cutaneous 
layer  of  muscular  fibres,  termed  the  dartos.  The  scrotum  is 
divided  into  two  chambers,  one  testis  being  lodged  in  each,  by  a 
membranous  partition,  or  septum.  Each  testicle  is  loosely  con- 
tained in  a  sac,  formed  by  an  external  serous  membrane,  the 
tunica  vaginalis,  derived  from  the  peritoneum,  which  forms  a 
cavity  for  its  reception  similar  to  that  of  other  serous  membranes. 
This  tunic  is  reflected,  hke  those  of  other  cavities,  over  the  body 
of  the  organ ;  and  the  reflected  portion,  which  is  called,  from  its 
white  colour,  the  tunica  albuginea,  forms  the  proper  capsule  of 
the  testis.  When  this  latter  tunic  is  divided,  the  testis  is  found  to 
consist  of  a  flattened  oval  substance,  to  the  upper,  outer,  and 
back  part  of  which  a  narrow  and  flat  slip  of  substance,  called  the 
epididymis,  is  found  adherent. 

806.  The  substance  of  the  testicle  is  extremely  vascular,  and 
the  ultimate  branches  of  its  spermatic  arteries  are  collected  into 
small  bundles  of  fine  convoluted  vessels,  separated  from  one 
another  by  septulce,  or  membranous  partitions.  From  these  the 
v>asa  seminifera,  or  beginnings  of  the  excretory  ducts,  take  their 
rise,  and  gradually  unite  to  form  a  smaller  number  of  canals  of 
larger  diameter,  but  exceedingly  tortuous  in  their  course.  On 
arriving  at  the  surface  and  back  part  of  the  testicle,  they  suddenly 
become  straight,  assuming  the  name  of  the  vasa  recta ;  they, 
however,  agatn  subdivide,  and  their  branches  have  very  numerous 
communications  with  one  another,  composing  the  net-work  of  tubes 
called  the  corpus  highmoriammi,  or  the  rete  testis.  From  the  rete 
testis  arise  the  ducts  denominated  the  vasa  efferentia,  which,  after 
being  again  contorted  into  numerous  convolutions,  form  the  conical 


336  REPRODUCTIVE    FUNCTIONS. 

bodies  called  co7ii  vasculosi;  these  again,  alternately  join  to  form 
the  epididymis,  already  mentioned,  which  consists  of  one  slender 
tube,  of  enormous  length,  coiled  upon  itself  into  a  small  compass.* 
The  epididymis  at  length  emerges,  in  the  form  of  a  tube  of  larger 
diameter,  which  is  the  vas  deferens,  and  which  ascends  along  the 
spermatic  cord  towards  the  abdomen.  On  tracing  these  ducts 
into  the  pelvis,  we  find  them  passing  up  by  a  circuitous  route 
through  the  spermatic  passage,  and  on  reaching  the  pelvis,  again 
descending  by  the  lower  side  of  the  bladder,  to  the  under  part  of 
its  cervix.  Each  duct  is  here  connected  with  an  oblong  mem- 
branous bag,  called  the  vesicula  seminalis,  which  is  a  long  blind 
sac,  folded  many  times  upon  itself;  its  open  extremity  entering 
the  vas  deferens  at  an  acute  angle.  These  sacs  are  supposed  to 
be  receptacles  for  the  retention ^and  accumulation  of  semen,  until 
the  time  when  it  is  required  to  be  expelled.  But  Hunter  remarked 
that  the  fluid  contained  in  them  is  somewhat  different  from  that 
obtained  from  the  seminal  ducts  of  the  testicle  itself;  and  he 
therefore  supposed  that  these  vesicles  secrete  a  peculiar  fluid 
which  may  perhaps  dilute  and  add  to  the  bulk  of  the  semen.  He 
even  contended  that  the  proper  office  of  these  cavities  is  not  that 
of  reservoirs  of  semen ;  supporting  his  opinion  by  arguments 
derived  from  comparative  anatomy,  which  furnishes  many  exam- 
ples where  no  direct  communication  exists  between  them  and  the 
vas  deferens,  and  others  where  these  vesicles  are  entirely  absent. 
Notwithstanding  these  analogies,  the  prevaiUng  opinion  is  in  favour 
of  the  vesiculffi  seminales  in  man  being  reservoirs  of  the  seminal 
secretion. 

807.  From  the  vesiculse  seminales  and  the  vas  deferens,  the 
semen  is  occasionally  discharged  through  a  duct  common  to 
both,  and  about  half  an  inch  in  length,  which  perforates  a  body 
called  the  prostate  gland,  and  then  opens  on  each  side  into  a  canal, 
termed  the  urethra,  which  is  continued  from  the  urinary  bladder, 
close  to  a  small  eminence  in  that  canal,  termed  the  verumontanum, 
or  caput  gallinaginis.  The  prostate  gland  is  of  the  size  of  a  small 
chestnut ;  in  shape  it  resembles  a  heart,  with  the  apex  directed 
forwards.  Its  texture  is  firm  and  tough ;  it  is  divided  into  two 
lateral  lobes,  and  one  anterior  lobe,  and  contains  a  great  number 
of  follicles,  into  which  a  white  opaque  viscid  fluid  is  secreted. 
This  secretion  is  discharged  by  ten  or  twelve  excretory  ducts 
opening  obliquely  into  the  urethra,  in  a  furrow  at  the  side  of  the 
verumontanum. 

808.  The  urethra  is  a  canal,  lined  by  a  mucous  membrane, 
serving  the  double    purpose   of  discharging  the  urine  and  the 

*  The  whole  length-of  the  excretory  vessels  of  the  testes  is  very  extraordi- 
nary. Their  diameter  has  been  stated  to  be  no  greater  than  the  200th  part  of 
an  inch ;  and  it  has  been  estimated  that  the  total  length  of  the  vessels  which 
compose  one  of  the  testes  amounts  to  more  than  500  feet. 


THE    MALE    SYSTEM. 


337 


semen.  As  it  proceeds  forwards  from  the  neck  of  the  bladder, 
it  passes  through  the  prostate  gland,  on  emerging  from  which  it 
becomes  more  contracted  in  its  diameter,  and  passes  under  the 
symphysis  pubis.  At  this  part,  for  the  length  of  about  an  inch, 
it  is  supported  only  by  firm  cellular  and  ligamentous  membranes; 
this  part  of  the  canal  is  termed  the  membranous  portion  of  the 
urethra.  It  is  then  dilated  into  what  is  called  the  bulh,  or  sinus 
of  the  urethra  ;  and  it  afterwards  receives  the  ducts  of  several 
mucous  glands,  which  have  been  denominated  the  glands  of 
Coivper,  and  which  are  generally  very  minute,  but  sometimes 
have  the  size  of  peas.  One  of  these  is  placed  on  each  side  of  the 
membranous  portion  of  the  urethra,  below  which  they  are  united 
by  an  isthmus  ;  and  the  duct  of  each^  about  three  inches  in 
length,  opens  by  perforating  the  mucous  membrane  lining  the 
spongy  body  of  the  penis.  Mucus  is  also  furnished  to  various 
parts  of  the  canal  by  lacunce  provided  for  that  purpose.  AX  its 
bulbous  part,  the  urethra  takes  a  considerable  curve  forwards, 
and  is  surrounded  in  the  rest  of  its  course  by  a  peculiar  erectile 
texture,  denominated  the  corpus  spongiosum  urethrtB.  This  sub- 
stance is  expanded,  at  the  extremity  of  the  penis,  into  what  is 
termed  the  glans,  which  is  covered  by  a  fold  of  the  skin  called 
the  prepuce.  The  corpora  cavernosa  are  the  cylindrical  bodies 
which  compose  the  chief  bulk  of  the  penis.  They  arise  by  two 
crura,  one  from  each  ascending  ramus  of  the  os  ischii,  and  are 
chiefly  composed  of  the  peculiar  structure,  termed  the  erectile 
tissue  (see  §  434).  At  its  extremity,  the  urethra  is  considerably 
narrower  than  where  it  passes  along  the  corpus  spongiosum. 

809.  These  parts,  namely,  the  glans  and  corpora  cavernosa 
penis,  and  the  corpus  spongiosum  urethras,  consist  principally  of 
large  convoluted  veins,  which  in  the  last  named  part  are  particu- 
larly dilated  and  branched,  and  are  bound  together  and  crossed 
in  various  directions  by  ligamentous  bands  and  fibres.  This 
arrangement,  by  obscuring  the  connexions  which  the  veins  have 
with  one  another,  as  well  as  their  tortuous  course,  has  led  to  the 
mistake  that  has  so  long  prevailed  among  anatomists,  of  ascrib- 
ing to  these  bodies  a  cellular  structure.  These  bands  appear  to 
have  been  provided  for  the  purpose  of  limiting  the  distention  of 
the  vessels,  and  adding  to  the  rigidity  occasioned  by  the  accumu- 
lation of  blood  in  the  venous  convolutions  during  erection.  The 
means  by  which  the  blood  is  made  to  pass  from  the  small  arteries 
into  these  convoluted  veins,  is  not  clearly  understood.  Professor 
Milller*  has  lately  discovered  a  remarkable  set  of  minute  dilated 
and  ramified  branches,  which  he  terms  arlerice  helicince,  and 
which  are  appended  to  the  terminal  twigs  of  the  arteries  distri- 
buted on  the  sides  and  interspaces  of  the  venous  cavities  in  the 

*  Archiv.  fiir  Physiol.  &c.  1835.  pp.  27  and  220. 
29 


338  REPRODUCTIVE    FUNCTIONS. 

penis  of  man  and  several  animals,  and  which  he  represents  as 
projecting  into  the  interior  of  the  veins,  and  pouring  their  blood 
into  them  ;  a  mechanism  which  must  doubtless  have  some  direct 
relation  with  the  process  of  erection.*  Dr.  Houston-f  has  de- 
scribed some  muscles,  under  the  name  of  compressores  vence 
dorsalis  penis,  to  the  contraction  of  which,  and  the  consequent 
impediment  to  the  return  of  the  blood  from  the  penis,  he  attri- 
butes the  erection  of  that  organ.  It  is  more  probable,  however, 
that  this  effect  is  produced  principally  by  an  altered  action  of  the 
blood-vessels  themselves,  and  is  analogous  to  the  turgid  state  of 
the  vessels  which  occurs  in  blushing,  than  is  owing  to  any  me- 
chanical cause.  The  purpose  served  by  the  dilatation,  elonga- 
tion, and  rigidity  of  the  male  organ,  effected  by  this  vascular- 
action,  is  obviously  that  of  enabling  it  to  penetrate  to  a  sufficient 
distance  into  the  female  organ  during  coition,  for  the  conveyance 
of  the  semen  to  those  parts  of  the  latter  whose  office  it  is  to 
carry  it  on  to  the  ovulum  which  it  is  intended  to  fecundate. 
With  this  view,  the  secretions  from  the  testes,  vesiculse  semJnales, 
prostate  gland,  and  the  glands  of  Cowper,  are  poured  together 
into  the  bulb  of  the  urethra,  and  thence  expelled  with  force  by 
the  action  of  the  muscles  called  the  ejaculatores  seminis. 

810.  The  seminal  fluid,  which  acts  so  important  a  part  in  the 
process  of  generation,  has  at  all  times  attracted  much  atten- 
tion. It  is  found  to  be  considerably  heavier  than  water,  and  to 
have  a  peculiar  odour,  which  increases  on  keeping;  to  exhibit 
alkaline  properties,  and  to  give  off  ammonia  when  heated.  From 
the  analysis  of  Vauquelin,  it  appears  that  human  semen  contains 
six  per  cent,  of  animal  mucus,  three  of  phosphate  of  lime,  and 
one  of  uncombined  soda ;  the  rest  being  water.  The  phosphate 
«f  lime  is  deposited  in  crystals  when  the  fluid  is  at  rest.  But  the 
most  remarkable  circumstance  in  its  composition  is,  the  constant 
presence  of  immense  number  of  microscopic  animalcules,  the 
form,  apjiearances,  and  size  of  which  are  different  in  almost  every 
different  animal ;  but  in  each  species  of  the  more  perfect  animals, 
the  kind  of  animalcules,  like  that  of  the  entozoa,  is  constant  and 
determinate.  Leewenhoek  claims  the  merit  of  having  first  dis- 
covered them ;  but  the  priority  of  this  discovery  is  assigned  by 
Haller  to  Ludwig  Hamm,  who,  when  a  student  at  Leyden,is  said 
to  have  observed  them  in  the  year  1677.     Another  claimant  of 

*  [The  researches  of  Valentin  (Mailer's  Archiv.,  and  Lond.  Med.  Gaz. 
June  23,  1838,  p.  543,)  are  not  in  accordance  with  those  of  Miiller. 
The  result  of  numerous  examinations  has  convinced  him,  that  the  helicine 
arteries  are  not  peculiar  vessels,  but  merely  minute  arteries  that  have  been 
divided  or  torn,  and  that  the  real  distribution  of  the  vessels  of  the  corpora 
cavernosa  follows,  in  every  respect,  the  most  simple  laws.] 

f  Dublin  Hospital  Reports,  vol.  v. 


THE    MALE    SYSTEM. 


339 


the  discovery  is  Hartsoeker,*  but  apparently  on  no  good  grounds. 
An  account  of  the  controversy  that  arose  on  this  subject,  is  given 
by  Dr.  Bostock.f  Doubts  were  at  one  time  entertained  of  the 
fideUty  of  the  representations  of  these  singular  beings  given  by 
Leewenhoek  ;  but  they  have  been  wholly  removed  by  the  later 
researches  of  Spallanzani,  and  the  still  more  recent  inquiries  of 
Prevost  and  Dumas.  These  animalcules  have  a  definite  figure, 
consisting  of  a  flattish  rounded  head,  from  which  proceeds  a  long 
tail,  exhibiting  constant  undulatory  movements.  They  are  ac- 
cordingly classed  by  naturalists  under  the  title  of  spermatozoa,  as 
a  species  of  the  genus  cercaria,  among  the  infusoi'ia.J 

811.  It  would  appear  from  the  elaborate  researches  of  Prevost 
and  Dumas,  that  these  spermatic  animalcules  are  found,  at  one 
time  or  other,  in  the  semen  of  almost  all  the  animals  in  which 
they  have  been  sought  for ;  but  at  that  period  of  their  life,  and  in 
that  season  of  the  year  only,  when  the  animals  in  which  they 
exist  are  fit  for  procreation.  They  are  almost  always  present  in 
the  fluid  secreted  by  the  testicles,  and  very  often  in  that  of  the 
vesiculffi  seminales,  into  which  they  have  doubtless  been  intro- 
duced along  wath  the  fluid  derived  from  the  testicles.  Hence  it 
has  been  concluded,  that  their  presence  is  intimately  connected 
with  the  power  of  propagation ;  and  may  be  essential  to  that 
process.  Wagner  infers  from  his  observations,  that  these  ani- 
malcules are  subject  to  remarkable  changes  of  form  at  difl'erent 
periods,  and  that  they  even  go  through  a  regular  gradation  of 
development;  and  phenomena  leading  to  the  same  conclusion 
have  been  observed  by  Dr.  Allen  Thomson. § 

812.ylt  is  not  until  the  period  of  puberty  that  the  generative 
organs  are  fully  developed,  and  become  capable  in  either  sex,  of, 
exercisiing  their  proper  functions.  Prior  to  this  period,  the  phy- 
sical character  of  the  two  sexes  is  nearly  the  same  :  there  is  the 
same  dehcacy  of  complexion,  the  same  high  pitch  of  the  voice, 
and  the  same  slightness  of  (figure.  But  the  development  of  the 
sexual  organs  appears  to  exercise  a  peculiar  and  specific  influ- 
ence over  the  system  at  large,  aflfecting  the  growth  of  the  rest  of 
the  frame,  and  modifying  both  its  physical  and  mental  powers. 
The  attainment  of  this  condition  is  more  tardy,  by  two  or  three 
years,  in  the  male  than  in  the  female ;  and  the  age  at  which  it 
takes  place,  differs  in  different  climates,  and  in  persons  of  different 
temperaments,  modes  of  life,  and  circumstances  of  physical  and 
moral  education.  It  occurs  at  an  earlier  age  in  southern  than  in 
northern  climates;  in  this  country  generally  appearing  in  the 
male  between  the  ages  of  fifteen  and  eighteen  years ;  and  in  the 

*  Essai  de  Dioptrique,  art.  88,  p.  227. 

•j-  Elementary  System  of  Physiology,  p.  642,  note.  / 

^   [See,  on  this  subject,  Dunglison's  Physiology,  3tl  edit.  ii.  330,] 
§  Cyclopaedia  of  Anatomy  and  Physiology,  art.  Generation,  p.  4t)0. 


340  '  REPRODUCTIVE    FUNCTIONS. 

female  from  that  of  thirteen  to  sixteen ;  but  in  the  hottest  regions 
of  the  great  continents,  girls  are  said  to  arrive  at  puberty  at 
ten,  or  even  at  nine  years  of  age ;  and  in  the  northernmost  parts 
of  Europe,  not  till  that  of  from  fifteen  to  eighteen.  The  arrival 
of  this  period  is  retarded  by  habits  of  active  bodily  exertion. 

813.  The  characteristic  changes  induced  by  puberty  in  the 
male  besides  the  development  of  the  genitals,  and  the  secretion  of 
the  seminal  fluid,  are  the  enlargement  of  the  larynx,  which 
changes  the  quality  of  the  voice ;  the  growth  of  the  beard  on  the 
chin,  upper  lip,  and  cheek,  and  of  an  increased  quantity  of  hair 
on  the  rest  of  the  body,  and  especially  on  the  pubes ;  the  enlarge- 
ment of  the  chest  and  shoulders;  an  increase  of  physical  activity 
and  power;  a  greater  capability  of  enduring  fatigue;  an  exalta- 
tion of  the  active  powers  ,of  the  mind,  and  of  the  qualities  of 
courage  and  resolution. 

814.  The  act  of  sexual  union  is  prompted  by  instinctive  feel- 
ings, experienced  by  both  sexes,  and  which  generally  depend  on 
the  condition  of  the  body,  and  of  the  genital  organs  in  particular, 
which  are  then  in  a  state  of  high  excitement.  This  mental  feel- 
ing, and  the  local  aflection  appear  to  be  intimately  associated 
together,  and  mutually  produce  one  another.  According  to  the 
doctrines  of  phrenology,  the  cerebellum  is  supposed  to  be  that 
particular  part  of  the  encephalon  which  presides  over  the  sexual 
function;  and  to  be,  in  a  word,  the  sensorium  commune  of  the 
feelings  relating  to  it ;  that  is,  the  part  to  which  impressions  of  a 
sexual  kind  proceed,  and  from  which  all  sexual  desire  emanates; 
and  to  be  the  source  of  that  power  by  which  the  generative  or- 
gans execute  their  appropriate  functions.  Dr.  Allen  Thomson, 
after  enumerating  the  proofs  alleged  in  favour  of  this  hypothesis,* 
observes,  that  he  is  not  inclined  to  adopt  it  as  established  on  suffi- 
ciently accurate  and  extensive  data;  and  remarks,  that  the  com- 
parative anatomy  of  the  brain,  (in  which,  rather  than  in  experi- 
ments on  animals,  he  would  be  disposed  to  place  much  reliance, 
from  the  acknowledged  difficulty  of  making  correct  deductions 
as  to  function,  from  the  effects  of  morbid  alteration  or  artificial 
injury  of  the  encephalon,)  affords  very  few  arguments  in  favour 
of  the  phrenological  doctrine,  and  furnishes  several  facts  which 
militate  strongly  against  it.  (See  the  article  Phrenology  in  the 
Appendix.) 


Sect.  IV. —  The  Female  System, 

815.  The  female  generative  system  of  organs,  having  to  perform 
the  offices  of  receiving,  conducting,  and  applying  to  the  ovulum 

*  Cyclopsedia,  &c.  p.  444. 


THE    FEMALE    SYSTEM.  341 

the  seminal  fluid,  of  conveying  tiie  ovum  into  a  situation  where  it 
can  be  evolved  and  properly  nourished,  and  of  bringing  it  forth  at 
the  appointed  period  into  the  world,  is  necessarily  much  more 
complicated  and  elaborate  than  the  male  system.  The  part  per- 
formed by  the  male  is  quickly  accomplished,  while  the  female  has 
to  execute  a  long  series  of  processes,  which  require  a  considerable 
time,  and  are  connected  with  important  changes  in  the  economy. 

816.  The  ovaria,  of  which  we  have  already  described  the 
structure  and  offices,  are  connected  with  a  hollow  muscular  organ, 
termed  the  uterus,  matrix,  or  icomb,  by  two  ducts,  called,  from  the 
name  of  the  anatomist  who  first  described  them  correctly,  the 
Fallopian  tubes.  They  commence  by  a  trumpet-shaped  mouth, 
opening  from  the  abdominal  cavity,  and  of  which  the  edges  are 
fringed  or  jagged  with  irregular  filaments,  or  Jimbrice,  as  they  are 
termed.*  The  mouth  of  the  Fallopian  tubes  are  endowed  with 
the  power,  on  certain  occasions  of  venereal  excitement,  of  attach- 
ing itself  to  the  adjacent  ovarium,  and  of  firmly  grasping  it.  The 
tubes,  each  of  which  is  about  five  inches  long,  in  their  progress 
towards  the  uterus,  soon  contract  in  their  diameter,  and  become 
exceedingly  narrow  at  their  termination  in  the  upper  and  lateral 
corner  of  the  triangular  cavity  of  that  organ.  They  are  enclosed 
in  the  folds  of  the  peritoneum  which  form  the  broad  ligaments  of 
the  uterus. 

817.  The  uterus  itself  is  a  compact,  dense,  membranous,  and 
fleshy  organ,  provided  with  a  copious  supply  of  blood-vessels, 
lymphatics,  and  nerves.  It  has  the  shape  of  a  flattened  pear,  and 
is  situated  in  the  pelvis,  between  the  rectum  and  the  urinary 
bladder.  The  outer  surface  of  the  uterus  is  covered  with  a 
reflected  portion  of  the  peritoneum,  which,  in  passing  from  the 
sides  of  the  uterus  to  the  sides  of  the  pelvis,  forms  the  broad  liga- 
ments already  mentioned,  or  the  Alee  Vespertilionis,  as  they  have 
been  called.  It  is  also  provided  with  round  ligaments,  connecting  it 
with  the  external  parts  of  the  pubes.  The  inner  surface  of  the 
uterus  is  lined  with  a  mucous  membrane.  The  existence  of 
muscular  fibres  in  its  substance  has  been  called  in  question  by 
many  anatomists,  and  it  is  certainly  difficult  to  demonstrate  their 
presence  ;  yet  the  extraordinary  mechanical  force  which  this 
organ  exerts  during  parturition  can  scarcely  be  ascribed  to  anv 
power  but  a  muscular  one.t  The  parts  of  the  uterus  are  distin- 
guished into  the  fundus,  which  is  the  broad  end  turned  towards 
the  abdomen,  the  body  and  the  cervix,  or  narrow  end.  The 
channel  of  the  cervix  uteri,  which  proceeds  from  the  lower  angle 
of  its  triangular  cavity,  leads  into  the  vagina,  which  is  an  elastic 

*  This  part  has  also  been  termed  the  morsus  diaboli. 

f  Dr.  Bostock  has  given  in  his  Physiology  an  enumeration  of  the  authors 
who  have  written  on  both  sides  in  this  controversy,  p.  648,  note.  [See,  also, 
Dunglison,  Op.  cit.  ii.  403.] 

29* 


342  REPRODUCTIVE    FUNCTIONS. 

membranous  canal,  opening  externally,  and  surrounding  at  its 
upper  part  the  cervix  uteri,  which  forms  a  protuberance  in  its 
cavity,  called  the  os  uteri,  or  os  tinccB,  from  its  supposed  resem- 
blance to  the  mouth  of  a  tench. 

The  membrane  which,  lines  the  vaginal  cavity  is  continued 
from  the  mucous  membrane  of  the  uterus,  but  is  thrown  into 
numerous  folds  and  wrinkles,  admitting  of  occasional  dilatation 
of  the  canah  This  is  surrounded  by  a  tissue  of  an  erectile  struc- 
ture, termed  plexus  restiformis,  or  corpus  cavern'osum  vagince. 

818.  The  external  parts  are  the  mons  veneris,  which  is  formed 
by  an  accumulation  of  adipose  substance  on  the  upper  part  of 
the  symphysis  pubis.  Below  this  are  the  labia  pudendi,  forming 
in  their  progress  towards  the  anus,  from  which  they  are  divided 
by  the  perineum,  what  was  called  by  the  French  anatomists 
fourcliette.  Between  the  labia  is  the  fossa  magna,  in  the  upper 
part  of  which  is  lodged  the  clitoris,  a  small,  -round,  and  spongy 
organ,  which  is  analogous  to  the  penis  in  its  erectile  structure, 
being  composed  of  two  corpora  cavernosa,  arising  from  the  tube- 
rosities of  the  OS  ischii,  and  terminating  in  an  impervious  glans, 
furnished  with  a  prepuce.  The  meatus  urinarius,  or  orifice  of  the 
urethra,  which  in  the  female  is  very  short,  opens  immediately 
below  the  clitoris.  From  this  part,  on  each  side  of  the  fossa, 
extends  the  nyni'phcB,  or  labia  minora,  which  are  membranous 
and  spongy  folds.  The  vulva,  or  orifice  of  the  os  externum,  is  in 
part  closed  by  a  transverse  membrane,  of  a  crescentic  form,  called 
the  hymen,  the  remains  of  which,  after  it  has  been  lacerated, 
compose  the  folds'  called  carunculce  myrtiformes. 

819.  The  changes  which  the  female  system  undergoes  at  the 
period  of  puberty  are  on  the  whole  as  considerable  as  those  of 
the  male,  although  many  of  the  external  characteristics  of  the 
state  of  childhood  are  still  retained,  such  as  the  deUcate  texture 
and  inferior  development  of  the  general  frame,  the  large  propor- 
tion of  subcutaneous  fat,  smooth  skin,  and  want  of  prominence 
in  the  muscles  of  the  trunk  and  limbs.  But  the  genital  system 
undergoes  a  considerable  and  rapid  development  at  this  period, 
the  breasts  enlarge,  the  pelvis  becomes  more  capacious,  and  a 
peculiar  periodical  secretion,  from  the  inner  surface  of  the  uterus, 
consisting  of  a  certain  quantity  of  sanguineous  fluid,  is  established. 
This  process,  which  is  termed  menstruation,  recurs  at  periods 
nearly  equal  to  a  lunar  month,  and  continues,  with  certain  inter- 
missions, determined  by  the  occurrence  of  pregnancy,  and  the 
performance  of  the  function  of  lactation,  as  long  as  the  organs 
are  capable  of  bearing  progeny,  which  is,  on  an  average,  a  terra 
of  thirty  years.  The  fluid  thus  discharged  is  generally  believed 
to  contain  less  fibrin  than  blood,  and  to  be  less  prone  to  putre- 
faction ;  it  evidently  contains  a  large  proportion  of  the  colouring 
particles  of  the  blood,  and  is   very  seldom  found  to  coagulate. 


THEORIES    OF    GENERATION.  343 

The  secretion  amounts,  on  an  average,  to  six  or  eight  ounces, 
and  usually  continues  for  about  four  or  five  days,  beginning  and 
leaving  oft' gradually,  and  being  most  abundant  towards  the  mid- 
dle of  the  period.  The  discharge  in  general  takes  place  slowly, 
or  drop  by  drop. 

820.  The  eflectual  fecundation  of  the  ovulum,  which  is  by  this 
change  converted  into  an  ovum,  and  its  removal  to  a  situation 
where  the  embryo,  then  first  brought  into  existence,  can  be  per- 
fectly developed,  constitute  the  process  of  concejption ;  but  the 
exact  nature  of  this  process,  as  well  as  the  precise  circumstances 
which  must  concur  for  its  successful  accomplishment,  have  been 
but  very  imperfectly  ascertained.  The  investigation  of  these 
phenomena  in  the  lower  animals,  however,  has  rendered  it  ex- 
tremely probable  that  Graafian  vesicles  are  continually  being 
produced  in  the  ovarium,  and  come  forwards  at  intervals,  during 
the  whole  period  of  female  fertility,  and  that  they  burst  in  suc- 
cession, and  shed  the  contained  ovula,  whether  sexual  intercourse 
take  place  or  not,  although  there  is  reason  to  believe  that  their 
maturity  is  hastened  by  this  act.  The  consequence  of  the  burst- 
ing of  one  of  these  vesicles  is  the  escape  of  the  ovulum  or  ovum, 
as  the  case  may  be,  and  its  passage  down  the  Fallopian  tube 
into  the  cavity  of  the  uterus.  The  lacerated  membrane  of  the 
vesicle  closes,  leaving  a  scar ;  the  internal  coat  becomes  thick- 
ened, and  a  yellow  substance  is  deposited  in  its  cavity,  giving 
rise  to  the  appearance  which  has  been  termed  a  corpus  luteum. 
The  presence  of  this  substance  is  a  certain  indication  of  the  pre- 
vious bursting  of  a  Graafian  vesicle. 

821.  Much  discussion  has  arisen  on  the  question  as  to  the  pre- 
cise time  when,  and  place  where,  the  ovulum  is  impregnated. 
There  seems  now,  however,  little  reason  to  doubt  that  the  semen, 
immediately  on  its  reception  into  the  uterus,  is  conveyed  by  the 
Fallopian  tubes  to  the  ovarium  itself,  and  then  comes  in  contact 
with  the  exposed  ovulum,  which  is  ready  for  fecundation.  On 
the  bursting  of  the  vesicle,  the  ovum  is  conveyed  down  the 
Fallopian  tube,  and  arrives  at  the  uterus,  where  the  changes  it 
next  undergoes  will  be  the  subject  of  future  inquiry. 


Sect.  V. — Theories  of  Generation. 

822.  Having  thus  stated  the  provisions  which  have  been  made 
by  nature  for  the  fecundation  of  the  ovulum,  by  the  concurrent 
offices  of  the  two  sexes,  we  may  here  examine  various  specula- 
tions and  opinions  which,  from  time  to  time,  have  been  enter- 
tained relative  to  the  nature  of  this  marvellous  and  mysterious 
process  ;  speculations  which,  although  for  the  most  part  exceed- 
ingly  hypothetical,  and  often  completely  visionary,  have  been 


344  REPRODUCTIVE    FUNCTIONS. 

dignified  with  the  appellation  of  theories  of  generation.  This  it 
is  our  intention  to  do  very  briefly,  and  to  notice  only  the  more 
important  of  these  theories ;  for  the  total  number  of  hypotheses 
which  have  been  advanced  on  this  subject  is  so  great,  that  their 
mere  enumeration  might  occupy  many  pages.  Drelincourt,  who 
lived  in  the  latter  part  of  the  seventeenth  century,  collected  from 
the  writings  of  his  predecessors  as  many  as  two  hundred  and 
sixty-two  "  groundless  hypotheses"  concerning  generation :  and 
"  nothing  is  more  certain,"  observes  Blumenbach,  "  that  Drelin- 
court's  own  theory  formed  the  two  hundred  and  sixty-third." 

823.  These  theories  may  be  arranged  according  as  they  relate 
to  the  action  of  the  parent  organs,  or  to  the  changes  in  the  egg 
occurring  during  the  formation  of  the  new  animal;  and  Haller 
divided  the  first  of  these  classes  into  three  divisions,  according 
as  the  oflspring  is  supposed  to  proceed  ;  first,  exclusively  from 
the  organs  of  the  male  parent,  which  is  the  theory  of  the  Sper- 
matist ;  or,  secondly,  entirely  from  those  of  the  female,  which  is 
that  of  the  Ovists;  or,  thirdly,  from  the  union  of  the  male  and 
female  products,  which  is  the  theory  of  Syngenesis.  The  second 
class,  again,  may  be  arranged  under  two  heads,  according  as  the 
new  animal  is  supposed,  first,  to  have  its  parts  rendered  visible, 
by  their  being  expanded,  unfolded,  or  evolved  from  a  previously 
existing  though  imperceptible  condition  of  the  germ,  which  is  the 
theory  of  evolution ;  or,  secondly,  to  be  newly  formed  from 
amorphous  materials  at  the  time  when  it  makes  its  appearance 
in  the  ovum,  which  constitutes  the  theory  o{  Epigenesis. 

824.  The  theory  of  the  Spermatists  regarded  the  male  semen 
as  furnishing  all  the  vital  parts  of  the  new  animal,  the  female 
organs  merely  affording  the  offspring  a  fit  receptacle  and  suitable 
materials  for  its  nourishment,  until  it  could  exist  by  the  indepen- 
dent exercise  of  its  own  functions.  One  of  the  earliest  supporters 
of  this  hypothesis  was  Galen;  but  its  modern  revival  dates  from 
the  period  of  the  discovery  of  the  seminal  animalcules,  which 
were  regarded  by  Leewenhoek  as  the  proper  rudiments  of  the 
foetus.  They  were  even  considered  by  some  to  be  miniature 
representations  of  men,  and  were  styled  homunculi;  one  author 
going  so  far  as  to  delineate  in  each,  the  body,  limbs,  features,  and 
all  the  parts  of  the  grown  human  body.  Even  Leewenhoek 
describes  minutely  the  manner  in  which  they  gain  the  interior  of 
the  ovum,  and  are  retained  after  their  entrance  by  a  valvular 
apparatus. 

825.  The  Ovists,  comprising  some  of  the  older  philosophers, 
such  as  Pythagoras  and  Aristotle,  maintained  that  the  female 
parent  affords  all  the  materials  necessary  for  the  formation  of  the 
offspring,  the  office  of  the  male  being  merely  to  awaken  the  dor- 
mant formative  powers  residing  in  the  female  products.  Malpighi 
and  Harvey  asserted  that  the  rudiments  of  the  fcEtus  are  derived 


THEORIES    OF    GENERATION.  345 

principally  from  the  female  ovum ;  an  opinion  which  was  also 
elaborately  defended  by  Yallisneri.* 

820.  The  theory  of  Syngenesis,  or  of  the  simultaneous  combi- 
nation of  products  derived  irom  both  sexes,  which  after  sexual 
intercourse,  are  supposed  to  unite  together  to  form  the  germ,  is 
also  of  very  ancient  date.  In  connexion  with  this  theory  may  be 
mentioned  that  modification  of  it  which  may  be  termed  the  theory 
of  metamorphosis,  according  to  which  a  formative  substance  is 
held  to  exist,  but  is  allowed  to  change  its  form,  in  order  to  be 
converted  into  the  new  being ;  as  also  the  hypothesis  of  Buffon, 
which  was  eagerly  adopted  by  Needham,  who  conceived  that 
certain  molecules  which  they  termed  organic,  and  which  they 
believed  universally  to  pervade  plants  and  animals,  were  all 
endowed  with  productive  powers,  which  enabled  them,  when 
placed  in  suitable  situations,  to  attract  one  another,  and  to  compose 
by  their  union  living  organized  bodies.  They  imagined,  that  in 
the  process  of  generation  the  superabundant  portion  of  these 
organic  molecules  were  accumulated  in  the  generative  organs, 
and  there  constituted  the  rudiments  of  the  offspring. 

827.  The  hypothesis  of  evolution,  or  of  pre-existing  germs, 
coincides  vvith  that  of  the  Ovists,  in  considering  the  foetus  as  solely 
the  production  of  the  female  ;  but  it  farther  assumes  that  it  already 
exists,  with  all  its  organs,  in  some  part  of  the  female  system 
previous  to  the  sexual  intercourse;  and  that  it  receives  no  proper 
addition  from  the  male  semen,  the  action  of  which  is  merely  that 
of  exciting  the  powers  of  the  foetus,  and  of  endowing  it  with 
vitality.  The  observations  of  Haller  with  respect  to  the  gradual 
enlargement  or  evolution  of  the  chick  during'the  process  of  incu- 
bation, were  conceived  to  lend  great  support  to  the  advocates  of 
this  theory,  of  whom  the  most  strenuous  and  enthusiastic  was 
Bonnet.  This  naturalist,  so  celebrated  for  the  boldness  of  his 
speculations,  contended,  not  only  that  the  whole  of  the  parts  of 
the  foetus  pre-exist  in  the  ovum,  before  they  actually  make  their 
appearance,  but  that  the  germs  of  all  the  animals  which  are  in 
future  to  be  born,  also  pre-exist  in  the  female  parent;  so  that  the 
ovaries  of  the  first  parents  of  any  species  of  animal,  contained 
the  gertris  of  all  their  posterity,  included  the  one  within  the  other, 
like  a  nest  of  boxes ;  from  which  comparison  he  termed  his  theory 
that  of  "  e7nboitement."  This  extravagant  notion  was  adopted  by 
many  physiologists,  principally  from  its  affording  some  kind  of 
explanation  of  what  no  other  theory  seemed  in  the  least  adequate 
to  solve.  Spallanzani,  in  particular,  was  a  zealous  defender  of 
the  hypothesis  of  pre-existing  germs.  It  appears,  however,  to  be 
totally  irreconcileable  with  the  phenomena  of  hybrid  productions, 
and  of  the  resemblance  which,  in  so  many  instances,  the  oflspring 
bears  to  its  male  parent. 

*  Delia  Generazione,  part  2. 


346  REPRODUCTIVE    FUNCTIONS. 

828.  We  have  already  mentioned  that  Harvey  and  Malpighi 
ascribed  the  formation  of  the  foetus  principally  to  the  powers  of 
the  female.  This  opinion  gave  origin  to  the  modern  theory  of 
Epigenesis,  first  clearly  promulgated  by  Caspar  Frederick  Wolff,* 
who  not  only  described  a  successive  production  of  organs,  of  the 
previous  formation  of  which  there  existed  no  trace ;  but  showed 
also,  that  after  parts  are  first  formed,  they  undergo  many  impor-  . 
tant  changes  in  their  shape  and  structure,  before  arriving  at  their 
finished  state.  The  more  recent  researches,  aided  by  delicate 
microscopical  observation,  of  Meckel,  Pander,  Baer,  Rathke, 
Oken,  Purkinje,  and  Valentin  ;  Serres,  Rolando,  Dutrochet,  Pre- 
vost  and  Dumas,  Coste,  and  others,  have  demonstrated  that  the 
theory  of  Epigenesis,  or  superformation  of  parts,  is  much  more  con- 
sistent with  the  observed  phenomena  than  that  of  evolution.  The 
facts  which  have  thus  been  brought  to  light  are  of  peculiar  interest 
with  reference  to  the  plans  of  nature,  into  which  they  give  us  a 
more  extended  insight,  by  exhibiting  new  and  unexpected  affini- 
ties between  remote  families  and  classes  of  animals  ;  by  showing 
that  at  one  period  the  type  of  their  formation  is  nearly  the  same, 
and  by  explaining  the  seeming  caprice  of  nature  in  instances  of 
monstrous  and  defective  formation.  But  to  attempt  adducing  the 
proofs  and  illustrations  of  these  positions,  would  engage  us  into 
details  requiring  an  extensive  survey  of  the  whole  animal  crea- 
tion, to  enter  into  which  would  occupy  more  space  than  is  com- 
patible with  the  limits  of  the  present  treatise.  We  must,  there- 
fore, content  ourselves  with  referring,  for  more  ample  elucidation 
of  this  subject,  to  the  Bridgewater  Treatise  on  Animal  and  Vege- 
table Physiology.] 


Sect.  VI. — Utero- Gestation. 

829.  On  the  arrival  of  the  ovum  in  the  cavity  of  the  uterus,  to 
which  we  have  traced  it  in  a  preceding  chapter,  the  first  object 
of  nature  is  to  effect  its  attachment  to  a  portion  of  the  inner  sur- 
face of  that  organ.  A  provision  for  this  purpose  has  already 
been  made,  even  whilst  the  ovum  was  contained  in  the  ovarium. 
A  vesicle,  first  noticed  and  described  by  Dr.  Barry,  is  formed 
around  the  ovum ;  the  granules  of  the  tunica  granulosa  become 
less  densely  aggregated  together,  and  gradually  pass  into  the 
state  of  fluid  albumen  ;  oil  globules  appearing  for  the  first  time 
to  take  their  place  on  the  surface  of  the  ovum.  This  fluid  he 
supposes  to  correspond  to  the  yolk  of  the  eggs  of  birds ;  and  the 

*  In  his  inaugural  dissertation,  entitled  Theoria  Generationis,  published  at 
Berlin  in  1759. 

I  Pan  iv.  chap.  ii.  on  Organic  Development ;  and  chap.  iv.  on  Unity  of 
Design.     Vol.  ii.  pp.  599,  625.     [A.mer,  edit.  ii.  437.] 


UTERO-GESTATION.  347. 

membranous  vesicle  above  mentioned,  in  which  it  is  enclosed, 
and  which  thus  forms  after  impregnation,  he  considers  as  the 
rudimental  chorion,  by  which  the  ovum  is  afterwards  attached 
to  the  uterus. 

830.  It  results  from  these  views,  that  mammalia  differ  from 
oviparous  animals  in  the  circumstance,  that  those  parts  of  their 
ovum  which  are  last  formed,  have  a  more  internal  origin ;  thus, 
the  first  portion  of  the  albumen  and  the  chorion  of  the  ovum  in 
mammalia,  originate,  not  in  the  oviduct,  but  in  the  ovary;  for 
which  purpose,  chiefly,  there  is  provided  the  very  large  quantity 
of  albuminous  fluid  in  the  Graafian  vesicle  ;  a  provision  which 
may  be  presumed  to  have  especial  reference  to  the  development 
of  the  embryo  within  the  body  of  the  mother.  The  chorion,  being 
formed  in  the  ovary,  it  is  an  ovum,  and  not  an  ovuhmi,  that  is 
■expelled  from  that  organ  in  mammalia.  On  the  other  hand,  in 
birds  it  is  an  ovulum,  and  not  an  ovum,  that  leaves  their  ovary; 
and  it  becomes  an  ovum,  and  receives  an  addition  of  the  albumen, 
or  yolk,  and  the  shell  membrane  in  their  oviduct,  and  then  be- 
comes analagous  in  all  its  parts  to  the  ovum  of  the  mammal  when 
the  latter  leaves  the  ovarium.  The  albumen,  in  the  form  of 
granules,  lines  the  ovisac,  constituting  the  membrana  granulosa; 
and  in  the  form  of  the  fiake  it  supports  the  ovulum  in  the  centre 
of  the  fluid  of  the  ovisac,  and  afterwards  supports  it  at  the  peri- 
phery of  the  latter,  sometimes  in  the  form  of  the  petasiolus 
granulosus,  or  cumulus  of  Baer.  It  closely  invests  the  ovulum  in 
the  form  of  the  tunica  granulosa ;  it  forms,  in  the  rabbit  at  least, 
and  probably  in  other  mammalia,  two  bands  or  ligaments,  termed 
the  chalazce,  which  are  conspicuous  in  birds ;  and  finally,  it  also 
provides  the  granulous  bands  by  which,  in  some  instances,  too 
sudden  a  discharge  of  the  ovum  of  the  Graafian  vesicle  is  pre- 
vented. 

831.  Dr.  Barry  finds  that  the  ova  of  the  rabbit  of  five  or  six 
days,  when  in  the  uterus,  are  in  bulk  about  eight  thousand  times 
that  of  the  ovulum  in  the  ovary,  and  have  three  concentric  mem- 
branes ;  namely,  first,  an  outer  vesicle,  (the  villous  chorion,) 
originating  in  the  ovary ;  secondly,  the  primitive  membrane  of 
the  yolk,  distended  so  as  to  fill  the  chorion  ;  and,  thirdly,  an  inner 
vesicle,  or  membrane,  which  has  been  called  the  hlastoderyna,  or 
germinal  membrane,  presenting  in  its  substance  a  central  spot, 
which  is  the  germinal  spot,  or  embryo.  Dr.  Allen  Thomson  has 
seen  this  spot  very  evident  in  the  ova  of  a  rabbit,  on  the  sixth 
day  after  impregnation.  It  corresponds  exactly  with  that  part 
called  the  cicatricula  in  the  egg  of  a  bird,  which  there  lies  imme- 
diately on  the  surface  of  the  yolk,  imbedded  in  a  disc  of  granules. 
In  the  centre  of  the  cicatricula,  a  dark  round  spot  is  seen,  termed 
the  colliquamentum,  which  contains  a  minute  vesicle,  discovered 
by  Purkinje,  and  which  bears  his  name.     This  vesicle,  which  is 


348  REPRODUCTIVE    FUNCTIONS. 

seen  in  ihe  ovulum,  afterwards  bursts,  and  leaves  in  its  place  a 
thin  and  tender  transparent  membrane.  In  the  centre  of  this 
transpai'ent  spot,  may  be  perceived,  seven  or-  eight  hours  after 
the  commencement  of  incubation,  with  the  aid  of  a  magnifying 
glass,  a  small  dark  line.  This  line,  or  primitive  trace,  as  it  has 
been  termed,  is  swollen  at  one  extremity,  and  is  placed  in  the 
direction  of  the  transverse  axis  of  the  egg.  The  rounded  end  is 
towards  the  left,  when  the  small  end  of  the  egg  is  turned 
from  us. 

832.  Having  traced  thus  far  the  changes  occurring  in  the  ovum 
before  it  becomes  attached  to  the  uterus,  we  shall  defer  the  consi- 
deration of  the  subsequent  stages  of  its  evolution  to  a  future 
section,  and  here  attend  to  the  changes  which  have  in  the  mean 
time  taken  place  in  the  uterus,  with  a  view  to  prepare  it  for 
the, office  it  has  now  to  perform. 

833.  A  change  has  already  taken  place  in  the  uterus,  prepara- 
tory to  the  reception  of  the  ovum,  and  before  its  arrival  in  that 
cavity.  An  increased  flow  of  blood  is  directed  towards  that 
organ.  A  substance,  consisting  of  lymph,  or  organizable  fibrin, 
exudes  from  its  interior  surface,  furnishing  it  with  a  soft  flaky 
lining,  which,  when  the  ovum  is  received,  is  reflected  over  that 
body,  so  as  to  give  it  a  double  covering.  These  two  folds,  the 
one  being 'in  contact  with  the  uterus,  and  the  other  with  the 
ovum,  constitute  the  two  layers  of  the  memhrana  decidua;  the 
former  portion  being  termed  the  decidua  vera,  and  the  latter,  the 
decidua  refiexa."*  This-  membrane  soon  becomes  organized,  and 
highly  vascular.!  The  vessels  in  the  progress  of  growth,  are  in 
some  parts  much  dilated,  so  as  to  form  sinuses,  which  are  ulti- 
mately intermingled,  though  by  no  means  continuous,  with  the 
blood-vessels  of  the  fostus.  These  latter  blood-vessels,  consisting 
of  the  umbilical  arteries  and  veins,  of  which  the  trunks  are  col- 
lected in  the  umbilical  cord,  have  passed  to  the  chorion,  which 
by  the  end  of  the  first,  and  during  the  second  month  of  pregnancy, 
has  acquired  a  villous  external  surface.  At  the  end  of  this  period, 
the  branches  of  these  vessels  penetrate  and  ramify  in  these  villi, 
which  become  thoroughly  vascular ;  and  this  thickening  and 
vascularity  is  concentrated  on  one  side  of  the  chorion,  generally 
on  that  which  is  adjacent  to  the  fundus  of  the  uterus,  forming  the 
body  called  the  placenta.     This  body  is  of  a  flattened  oval  shape, 

*  [The  very  existence  of  a  decidua  reflexa  iias  been  a  matter  of  dispute  ; 
and  by  those  who  admit  it,  the  mode  of  formation  and  arrang^ement  has  been  a 
topic  for  discussion.  In  the  different  views  of  obstetrical  Physiologists,  the 
reader  is  referred  to  Velpeau's  Embryologie,  Paris,  1833,  or  to  Dunglison's 
Physiology,  3d  edit.  ii.  308,  in  which  they  are  all  detailed.] 

I  [It  is  denied  by  many,  that  the  decidua  is  supplied  with  vessels.  Vel- 
peau  regards  it  as  vv'holly  inorganic ;  and  denominates  it,  in  consequence, 
"anhistoiis"  membrane,  from  a.]/,  primitive,  and  ivto;,  texture,  that  is,  mem- 
brane devoid  of  texture  or  organization.] 


PARTURITION.  349 

from  six  to  eight  inches  in  breadth,  and  from  an  inch  to  an 
inch  and  a  quarter  in  thicl<ness  at  the  middle  part,  becoming 
thinner  towards  the  edges.  It  occupies  about  a  fourth  part 
of  the  chorion,  and  at  birth  is  a  pound  in  weight.  In  rumi- 
nant quadrupeds,  the  substance  corresponding  to  the  human 
placenta,  is  confined  to  a  number  of  circular  and  spongy  eleva- 
tions, varying  in  number  from  thirty  to  one  hundred,  which  are 
termed  cotyledons.  The  human  placenta  is  evidently  formed  of  a 
structure  essentially  the  same,  composed  of  many  lobes  consoli- 
dated by  contact  into  one  organ.  It  has  very  generally  been 
supposed  that  the  placenta  is  of  a  cellular  structure,  and  that  the 
arteries  and  veins  of  the  uterus  communicate  with  its  cells;  but 
the  recent  researches  of  Dr.  Robert  Lee,*  renders  it  very  doubtful 
if  these  inter-placental  cells  really  exist. 

834.  In  proportion  as  the  foetus  grows,  the  uterus  enlarges,  and 
about  the  fifth  month  it  rises  out  of  the  pelvis,  and  rests  against 
the  front  of  the  abdomen.  As  it  enlarges,  the  distinction  between 
the  body  and  the  cervix  is  lost ;  the  os  tineas  is  flatteffed,  and 
forms  only  a  small  rugous  hole,  not  easily  discernible  ;  and  it  is 
closed  by  a  tough  glutinous  matter,  which  is  fixed  in  the  in'egu- 
larities  of  the  surface. 


Sect.  VII. — Parturition. 

835.  The  ordinary  period  of  utero-gestation  is  forty  weeks ; 
on  the  expiration  of  which  the  uterus  takes  on  itself  a  new  kind 
of  action;  its  contractility,  which  had  lain  dormant  for  so  long 
a  time,  is  now  suddenly  and  powerfully  excited.  A  mucous 
discharge  takes  place  from  the  vagina,  the  external  passage  is 
relaxed,  and  slight  pains  are  felt  in  the  back  and  loins,  which 
usher  in  the  real  pains  of  labour.  These  are  occasioned  by 
powerful  contraction  of  the  uterus,  accompanied  by  a  strong 
action  of  the  diaphragm  and  abdominal  muscles;  and  they  are 
repeated  at  short  intervals.  Impelled  by  this  pressure,  the  mem- 
branes of  the  foetus  project  into  the  vagina,  and  dilate  the  os 
tineas ;  on  their  bursting,  the  liquor  amnii  escapes,  and  at  the 
next  pain  the  pressure  of  the  uterus  falls  directly  on  the  foetus. 
The  head  of  the  foetus  gradually  descends,  urged  on  by  succeeding 
spasms,  the  occiput  foremost,  the  long  axis  of  the  head  being 
disposed  obliquely  across  the  lesser  basin  of  the  pelvis.  The 
occiput,  as  the  external  parts  yield,  glides  off  the  inclined  surface 
of  the  ischium,  presenting  at  the  orifice  of  the  vulva,  and  bringing 
at  the  same  time  the  long  diameter  of  the  shoulders  to  corres- 
pond with  the  greatest  breadth  of  the  pelvis,  and  the  head  being 

*  Philosophical  Transactions  for  1832. 
30 


350  KEPRODUCTIVE    FUNCTIONS. 

thus  disengaged,  the  trunk  follows.  After  a  short  time,  fresh 
pains  return,  and  the  placenta  and  membranes  being  detached 
from  the  uterus,  come  away.  In  the  majority  of  natural  births, 
labour  is  completed  in  from  four  to  six  hours.  The  uterus  then 
very  slowly  and  insensibly  contracts,  so  as  to  diminish  the  ample 
cavity  which  has  been  rendered  vacant,  and  at  the  same  time  its 
volume  is  reduced  by  absorption.  During  the  return  of  the 
uterus  to  its  former  state,  a  discharge,  at  first  tinged  with  blood, 
and  afterwards  of  a  whitish  colour,  termed  the  lochia,  ensues, 
which  lasts  for  several  days.* 


Sect.  VIII. — Lactation. 

836.  The  function  by  which  nourishment  is  prepared,  of  a  nature 
suited  to  the  early  periods  of  infant  life,  belongs  to  the  reproductive 
class.  The  fluid  provided  for  this  purpose  is  the  Milk,  of  which 
we  have  already  examined  the  chemical  properties,  and  noticed 
the  qualities  which  peculiarly  fit  it  for  the  purpose  it  is  intended 
to  serve.  The  organs  which  prepare  it  are  the  mammoe,,  which 
are  glands  consisting  of  the  union  of  a  great  number  of  lobes, 
intermixed  with  adipose  substance,  and  remarkable  for  the  white- 
ness and  fineness  of  their  texture.  The  numerous  excretory  tubes 
from  these  lobules  unite  in  forming  ducts,  which  open  separately 
in  the  folds  of  the  integuments  of  the  nipple.  A  remarkable  sym- 
pathy is  observed  between  this  gland  and  the  uterus;  for  it  often 
enlarges  and  becomes  tender  for  a  few  days  before  each  monthly 
period.  It  enlarges  during  the  latter  months  of  pregnancy,  and 
the  brown  circle  surrounding  the  nipple,  or  areola,  as  it  is  called, 
assumes  a  dark  colour.  The  secretion  of  milk  would  naturally 
continue  until  the  middle  of  the  second  year,  if  the  child  were 
retained  at  the  breast  as  long  as  it  was  supplied.  During  the 
period  of  suckling,  the  menstrual  discharge  is  not  renewed,  but 
pregnanacy  may,  however,  again  take  place,  before  its  recurrence. 


Sect.  IX. — Fadal  Evolution. 

837.  In  judging  of  the  changes  which  take  place  in  the  human 
embryo  from  the  period  when  its  evolution  commences,  we  must 
be  guided  principally  by  those  which,  occurring  in  the  develop- 
ment of  that  of  the  chick,  furnish  the  best  means  of  following  the 
whole  succession  of  phenomena.  Commencing  the  inquiry,  then, 
from  the  appearance  of  the  primitive  trace  in  the  blastoderma,  or 
cicatricula,  already  described  (§  831),  we  find  this  part  gradually 

*  The  above  account  of  parturition  is  for  the  most  part  extracted  from 
Mr.  Mayo's  Outlines  of  ituman  Physiology,  as  presenting  a  very  clear  and 
compendious  account  of  the  phenomena. 


FffiTAL    EVOLUTION.  351 

dilating  in  bulk,  and  occupying  a  situation  between  the  two 
layers,  namely,  the  outer  and  the  inner,  into  which,  towards  the 
twelfih  or  fourteenth  hour  of  incubation,  this  cicatricuia  has 
divided  itself  The  outer  of  these  layers  is  called  by  Pander  the 
serous  layer ;  and  it  subsequently  gives  rise  to  the  nervous,  the 
musculai-,  the  osseous,  cartilaginous,  and  tegumentary  systems  of 
the  body.  The  innermost,  which  is  situate  in  contact  with  the 
yolk,  is  the  7nucous  layer,  whence  are  derived  the  alimentary  canal, 
and  the  glandular  and  pulmonary  systems.  A  third  layer  (the 
vasczilar  layei-),  is  afterwards  formed  in  the  interval  between  the 
two  former,  and  is  the  origin  of  the  sanguiferous  system  of  the 
foetus,  including  the  heart  and  all  the  blood-vessels.  The  respi- 
ratory system  is  the  product  of  the  combined  changes  which  this, 
together  with  the  last  mentioned  layer,  undergoes. 

838.  The  series  of  phenomena  which  present  themselves  in 
following  the  succession  of  changes  occurring  during  the  forma- 
tion of  the  vital  organs,  are  highly  curious,  and  afford  the  most 
splendid  instances  of  that  refined  intelligence  and  that  provident 
adjustment  of  a  long  series  of  means  for  the  effectual  accompHsh- 
ment  of  future  and  far  distant  ends,  which  strike  us  with  pro- 
found astonishment  when  we  penetrate  into  the  remoter  regions 
of  physiology,  removed  from  ordinary  observation.  It  would 
far  exceed  the  limits  within  which  we  must  confine  ourselves  in 
the  present  treatise,  to  give  the  detailed  history  of  these  organic 
changes.  We  must  content  ourselves,  therefore,  with  a  brief 
outline  of  the  principal  phenomena,  and  with  referring  to  works 
professedly  treating  on  this  subject,  for  more  copious  information 
on  this  highly  curious  department  of  physiology.* 

839.  On  the  outer  surface  of  the  serous  layer,  or  that  most 
distant  from  the  yolk,  there  are  raised  two  parallel  ridges,  which, 
joining  along  their  upper  margins,  form  a  canal;  in  this  canal, 
according  to  Baer  and  Serres,  a  semi-fluid  matter  is  deposited ; 
this  matter,  acquiring  consistence,  becomes  the  spinal  chord, 
with  a  pyriform  extremity,  which  last  is  the  rudiment  of  the 
the  future  head.  Roland,  Prevost,  and  Dumas,  on  the  other  hand, 
suppose  that  the  primitive  trace  is  itself  the  spinal  cord  and  brain, 
in  their  rudimental  state. 

840.  When  the  layei's  of  the  germinal  membrane  have  so  far 
expanded  as  to  cover  nearly  one-third  of  the  yolk,  they  no  longer 

*  The  reader  will  meet  with  mucii  instruction  on  these  subjects,  in  Dr. 
Allijn  Thomson's  papers  on  Embryology  in  the  Edinburgh  New  Philosophical 
Journal  ;  in  the  Cyclopaedia  of  Anatomy  and  Physiology,  by  Dr.  Todd ;  and 
also  in  Mr.  Mayo's  Outlines  of  Human  Physiology,  chap.  xv.  sect.  ii.  We 
would  also  beg  to  refer  to  the  summary  contained  in  the  Bridgewater 
Treatise  on  Animal  and  Vegetable  Physiology,  vol.  ii.  p.  599.  [Amer,  edit. 
ii.  408.]  The  greater  part  of  the  summary  given  in  the  present  article  is 
abridged  from  Mr.  Mayo's  work.  [See,  also,  Velpeau's  Embryologie  ou 
Ovologie  Humaine,  Paris,  1833,  and  Dunglison's  Physiology,  ii,  421.] 


352  REPRODUCTIVE    FUNCTIONS. 

retain  their  flat  and  uniform  appearance,  but  begin  to  exhibit 
various  folds,  which  afterwards  become  the  different  cavities  of 
the  body.  Those  of  the  mucous  layer  turn  downwards,  and 
whilst  its  remote  expansion  includes  within  it  the  yolk,  as  in  a  sac, 
the  inner  folds  close  inwards,  and  by  the  union  of  their  margins 
form  two  tubular  cavities,  one  at  each  endof  the  embryo,  commu- 
nicating in  the  middle  with  each  other,  and  also,  by  a  common 
opening,  with  the  cavity  of  the  yolk.  This  tube  is  the  nascent 
alimentary  canal. 

841.  The  first  rudiment  of  the  heart  is  perceptible  at  the 
anterior  part  of  the  vascular  layer,  which,  as  we-  have  already 
stated,  is  developed  between  the  serous  and  mucous  layers.  In 
the  mean  time,  the  surrounding  disc  of  the  cicatricula,  which 
continues  to  expand,  exhibits,  in  the  circumference  of  the  trans- 
parent area,  which  now  becomes  thicker  and  more  spongy,  numer- 
ous irregular  points 'and  lines  of  a  dark  yellow  colour.  These 
lines  gradually  extend,  unite  together,  first  into  small  groups,  and 
then  into  one  net-work,  which  composes  the  vascular  area.  The 
space  they  occupy  is  terminated,  on  each  side,  by  a  circular 
vessel,  of  larger  size  than  the  rest,  the  sinus  or  vena  terminalis, 
into  which  the  smaller  ramifications  of  the  vessels  open  at  the 
circumference,  whilst  towards  the  central  part  they  unite  into  a 
vessel  on  each  side,  the  two  o7Jiphalo-meseraic  arteries,  which 
penetrate  into  the  vascular  layer  of  the  embryo. 

842.  Simultaneously  with  these  changes,  all  the  important 
organs  of  the  body  are  formed  in  rapid  succession.  The  spinal 
cbrd  and  brain,  of  which  we  have  noticed  the  first  traces,  are 
quickly  developed  ;  the  former,  appearing  first  as  a  membranous 
tube,  the  latter,  as  three  vesicular  bodies ;  and  both  being  gra- 
dually filled  with  opaque  nervous  substances  of  two  , kinds,  the 
one  being  uniform,  the  other  filamentous.  The  nerves  next  ap- 
pear, but  w^iether  they  are  generally  formed  in  their  entire 
length  at  once,  or  are  growths  from  the  brain  or  spinal  cord,  or 
are  first  produced  at  their  farthest  extremity,  and  afterwards  ex- 
tended towards  the  central  organ,  are  points  not  yet  determined. 
Some,  however,  as  the  optic,  auditory,  and  olfactory  nerves,  are 
certainly  productions  from  the  cerebrum.  The  muscles  become 
visible  in  the  human  embryo  at  the  third  month  ;  they  are  then 
soft  and  gelatinous,  transparent,  of  a  light  yellow  tint,  and  not 
distinguishable  from  their  tendons.  Each  muscle  is  formed  at 
once  in  its  whole  length,  with  its  attachments  perfect.  The  eyes 
are  formed  at  a  very  early  period,  and  their  growth  is  rapid; 
they  are  situate  at  first  at  the  sides  of  the  head,  as  in  quadrupeds, 
and  subsequently  move  forwards.  The  iris  has  no  central  aper- 
ture, the  place  of  the  pupil  being  occupied  by  the  membrana 
pupillaris,  which  disappears  completely  before  birth.  The  organ 
of  hearing  is  formed  soon  after  the  eye.     The  substance  of  the 


FCETAL    EVOLUTION.  '  353 

bones  is  at  first  an  homogeneous  jelly,  enclosed  in  a  menhbrane, 
and  exhibiting  no  divisions  into  joints.  This  jelly  gradually  be- 
comes cartilaginous,  the  conversion  taking  place  irom  the  surface 
inwards.  It  is  gradually  replaced  by  ossific  matter,  which  grows 
from  the  interior,  resembling  a  process  of  crystallization.  Ossi- 
ficaiion  begins  in  the  human  embryo  in  the  seventh  week. 

843.  The  integument  is  the  outermost  fcetal  pi'oduct  of  the 
serous  layer,  which  gradually  spreads  like  a  mantle  over  all  the 
other  structures,  and  dpes  not  acquire  proper  strength  till  the 
middle  of  the  fcetal  period.  At  the  end  of  the  fifth  month  the 
body  is  covered  with  short,  whitish,  and  silky  down,  which, 
however,  disappears  in  the  seventh  month.  The  hair  of  the 
head  and  of  the  eye-brows,  and  the  nails,  are  formed  in  the  sixth 
month.  About  the  fifth  month  there  appears  on  the  body  a  yel- 
lowish-white greasy  substance,  at  first  thinly,  and  afterwards 
more  thickly  spread,  and  termed  the  vernix  caseosa.  The  limbs 
are  formed  originally  below  the  skin,  which  they  reach,  pushing 
out  like  little  globular  shoots,  in  the  sixth  week.  They  originally 
grow  straight  out  from  the  trunk.  The  upper  arm  is  next  laid  against 
the  breast,  the  fore-arm  drawn  upwards ;  the  thigh  is  bent  up  to 
the  belly,  the  leg  drawn  ^backwards  towards  the  thigh,  and  the 
feet  turned  in,  and  crossed,  with  the  soles  turned  inwards.  When 
the  fingers  are  first  formed,  they  are  contained  in  a  common 
mitten  of  skin,  which,  gradually  becoming  thinner  between  them, 
forms  a  web,  which  is  finally  absorbed. 

844.  Another  product  of  the  serous  layer  is  one  still  more  ex- 
ternal than  the  integument  of  the  foetus,  and  consisting  of  a  sac 
formed 'by  a  membrane  reflected  from  the  sides  and  from  either 
extremity  of  the  embryo,  so  as  to  enclose  a  space  behind  its  body. 
This  is  the  amnios,  which  forms  a  loose  bag  filled  with  a  liquid 
(the  liqiLor  amnii)  in  which  the  fostus  floats,  suspended  by  the 
umbilical  cord.  As  the  walls  of  the  trunk  close  in  front,  the 
circular  edge  by  which  the  amnois  is  attached  to  the  body  of  the 
embryo  becomes  proportionably  contracted ;  and  it  is  finally 
limited  to  the  umbilical  opening,  hereafter  to  be  noticed. 

The  communication  which  we  described  as  being  left  between 
the  intestinal  tube  and  the  cavity  of  the  yolk  bag,  or  vitelline  sac, 
and  which  in  birds  continues  open,  soon  becomes  closed  in  mam- 
malia, the  sac  assuming  the  form  of  the  intestinal  vesicle,  disco- 
vered as  such  by  Bojanus  in  the  ovum  of  the  sheep  ;  though  it 
had  been  before  seen  and  known  by  the  name  of  vesicula  alba ; 
it  disappears  by  the  third  month. 

845.  The  glandular  organs  which  communicate  with  the  ali- 
mentary canal  are  formed  by  the  extension  of  its  mucous  mem- 
brane in  the  form  of  tubular  productions,  shooting  into  small 
masses  of  matter  lodged  in  its  neighbourhood  ;  the  blind  ends  of 
the  tubes  being  often  dilated  into  spherical  pouches.     The  gall 

30* 


354  REPRODUCTIVE    FUNCTIONS. 

bladder  is,  in  like  manner,  formed  by  the  extension  of  a  tube, 
which  not  being  received  into  a  mass  of  elementary  matter,  en- 
larges into  a  simple  sac. 

846.  The  lungs  are  regarded  as  another  expansion  of  the 
mucous  layer  of  the  germinal  membrane,  growing  from  the  back 
part  of  the  oesophagus,  and  gradually  advancing  on  either  side  of 
the  aorta,  so  as  at  length  to  surround  it. 

847.  The  kidneys  are  preceded  in  the  embryo  by  a  substance 
first  noticed  by  Wolff,  and  called  after  him  the  Wolffian  bodies, 
or  false  kidneys,  which  originally  extend  the  whole  length  of  the 
spine,  from  the  heart  to  the  end  of  the  intestines ;  but  they  become 
afterwards  shorter,  and,  after  a  time,  diminishing  by  absorption, 
wholly  disappear.  They  appear  to  be  subservient  to  the  deve- 
lopment both  of  the  true  kidneys  and  of  the  testes  and  ovaria. 
The  bladder  and  urethra,  on  the  other  hand,  together  with  the 
external  genitals,  are  formed  partly  out  of  a  development  of  the 
extremity  of  the  intestine,  and  partly  by  fissure  and  folding  of  the 
integument,  in  the  following  manner. 

848.  There  is  first  the  production  of  a  bag  of  considerable 
length,  called  the  aUantois,  from  the  intestine,  or  that  part  of  it 
which  may  be  considered  as  the  cloaca;  subsequent  contractions 
of  the  sides  of  the  sac,  at  different  parts,  next  divide  it  into  two 
cavities,  the  proper  allantois  and  the  urinary  bladder ;  and  the 
lower  contraction  is  elongated  into  the  canal  of  the  urethra.  The 
separation  between  the  two  former  afterwards  closes,  and  the 
coalesced  membrane  forms  the  ligament  termed  the  urachus. 
The  urethral  tube  never  closes. 

849.  The  testes  and  ovaries  appear  in  mammalia  about  the 
sa  me  time  at  the  inner  and  fore  part  of  the  Wolflian  bodies,  attached 
to  them  by  a  fold  of  the  peritoneum.  From  each  testis  or  ovary 
there  descends  to  the  internal  ring  a  membranous  process,  which 
in  the  male  is  called  the  gubernaculum,  and  in  the  female  consti- 
tutes the  round  ligament.  It  passes,  in  either  sex,  along  the 
spermatic  passage  to  the  filaQientous  tissue  of  the  scrotum  or 
labium.  The  ovaries  descend  to  the  brim  of  the  pelvis;  the  testes 
pass  through  the  ring  into  the  scr-otum.    ,. 

850.  Every  organ  begins  to  be  formed  without  either  blood,  or 
blood-vessels  ;  the  circulation  in  them  being  established  solely  for 
the  purpose  of  subsequent  growth  and  perfection.  Even  the  heart 
is  formed  and  shaped,  and  its  texture  has  acquired  some  degree 
of  consistency,  and  it  displays  an  undulatory  motion,  before  the 
blood  has  reached  it.  We  have  already  described  the  formation 
of  vessels  and  of  blood  in  the  vascular  area ;  but  the  blood  is  at 
first  motionless.  It  afterwards  finds  its  way  from  thence  by  the 
omphalo-mesenteric  veins  to  the  heart,  whence  it  is  expelled 
along  the  aorta,  and  thence  again  carried  into  the  vascular  area ; 
thus  establishing  a  simple  circulation.     In  a  few  days  arterial 


rCETAL    EVOLUTION.  355 

branches  extend  froin  the  aorta,  and  venic  cava)  are  formed, 
establishing  the  systematic  circuhition.  Five  pair  of  branchial 
vessels  are  formed  from  the  aorta  in  the  neck,  the  oesophagus 
being  between  the  branches  on  each  side,  and  there  are  also  four 
openings  in  the  neck  of  the  embryo  on  each  side.  This  single 
heart,  branchial  arches,  and  openings,  are  permanent  parts  of  the 
structure  in  fishes.  In  the  mammalia,  these  branchial  clefts  soon 
close ;  the  heart  becomes  separated  by  the  growth  of  partitions 
in  each  ventricle  and  auricle,  into  two  separate  cavities,  and  the 
artery  is  divided,  in  like  manner,  into  an  aorta  and  pulmonary 
artery.  Some  of  the  arches  then  disappear ;  others  become 
permanent  aortic,  and  others  permanent  pulmonary  branches  ; 
and  the  foetus  is  becoming  prepared  for  pulmonary  respiration. 

851.  The  amnios,  closing  upon  the  shrunk  urachus,  forms 
with  the  umbilical  artery  and  veins,  and  a  connecting  gelatinous 
tissue,  the  umbilical  cord,  or  navel-string ;  connecting  the  foetus 
with  the  placenta,  which,  as  M'C  have  before  seen,  is  formed  by 
a  thickened  portion  of  the  chorion.  The  umbilical  vein  distri- 
butes part  of  its  blood  to  the  liver,  and  then,  under  the  name  of 
the  ductus  venosus,  joins  the  inferior  cava,  through  which  the 
mixed  blood  of  the  placenta  and  of  the  inferior  part  of  the  body 
is  carried  into  the  right  auricle  of  the  heart.  Part  of  this  blood 
passes  directly  from  the  right  to  the  left  auricle  through  the 
foramen  ovale,  which  is  an  aperture  in  the  yet  imperfect  septum 
of  the  auricles ;  the  remainder,  with  the  exception  of  the  small 
quantity  transmitted  to  the  yet  imperfectly  developed  lungs, 
passes  from  the  pulmonary  artery,  through  the  ductus  arteriosus 
directly  into  the  aorta.  The  offices  of  the  placenta  are  supposed 
to  be  those,  first,  of  introducing  nourishment,  transmitted  by  im- 
bibition from  the  maternal  to  the  foetal  blood,  through  the  mem- 
branes of  the  interjacent  vessels  of  the  mother  and  the  foetus; 
and,  secondly,  of  oxygenating  the  blood  of  the  foetus  by  impart- 
ing to  it  oxygen  from  the  same  source.  It  has  been  supposed  by 
many  that  the  foetus  derives  sustenance  from  the  liquor  amnii 
which  surrounds  it,  and  which  might  be  introduced  through  the 
mouth  into  the  stomach ;  but  this  opinion  is  now  very  generally 
abandoned.  It  is  true,  however,  that  the  stomach  of  the  foetus 
usually  contains  a  considerable  quantity  of  ropy  mucus,  but  with- 
out albumen.  This  last  substance  is  found  in  the  contents  of  the 
duodenum,*  and  the  great  intestines  contain  a  green  matter 
termed  meconium,  which  has  the  appearance  of  being  the  refuse 
of  a  kind  of  digestion.  It  has  been  conjectured  that  the  thymus 
.gland  has  some  relation  to  the  function  of  foetal  assimilation. 

*  See  a  paper  by  Dr.  Robert  Lee,  in  the  Philosophical  Transactions  for 
1829. 


356  KEPRODUCTIVE    FUNCTIONS. 


CHAPTER   XX. 

PROG-RESSIVE  CHANGES  IN  THE  ANIMAL  ECONOMY. 

852.  We  have  now  traced  the  history  of  the  changes  which 
the  human  system  undergoes,  from  the  earliest  rudimental  state  in 
which  it  exists  in  the  embryo,  tlirough  the  period  of  its  foetal  life, 
to  the  epoch  of  its  birth ;  when  it  is  ushered  into  the  world,  with 
organs  fitted  for  maintaining  a  comparatively  independent  exist- 
ence, yet  still  requiring  the  most  tender  offices  and  most  fostering 
care  of  that  parent,  of  whose  system  it  had  so  long  formed  a  part, 
and  from  which  it  has  been  so  recently  dissevered.  To  follow 
the  narrative  of  the  successive  alterations  which  take  place  during 
the  growth  of  the  system,  the  proportional  development  of  its 
several  organs,  and  the  acquisition  of  its  various  powers,  both 
corporeal  and  mental,  during  all  the  subsequent  epochs,  filling  up 
the  interval  between  the  cradle  and  the  grave,  composes  a  long 
chapter  in  human  physiology,  and  would  occupy  too  large  a  space 
for  the  present  treatise.  All  that  we  can  pretend  to  attempt  must 
be  a  faint  sketch  of  the  outlines  of  this  "  strange  eventful  history." 

853.  The  greatest  of  all  the  changes  which  occur  in  the  animal 
existence  of  every  human  being,  is  its  emergence  from  the  state 
in  which  it  was  dependent  for  its  immediate  supply  of  nourishment 
and  of  oxygen  on  the  blood  which  is  circulating  in  the  vessels  of 
its  parent.  On  its  birth,  which  cuts  oft'  the  placental  circulation, 
all  these  ties  are  at  once  dissevered.  A  new  element  surrounds  , 
it,  from  which  it  is  in  future  to  derive  the  principle  that  maintains? 
its  vital  energies.  The  placental  supply  is  superseded  by  respi- 
ration ;  and  the  first  gasp  of  air  received  by  an  instinctive  effort 
into  its  lungs  alters  at  once  the  whole  character  of  its  organic 
constitution.  It  is  now  a  breathing  animal ;  and  all  the  channels 
and  passages,  which  had  till  then  been  adapted  to  a  difi^erent  mode 
of  being,  have  now  become  useless,  or  rather  worse  than  useless, 
and  thev  must  give  way  to  a  new  order  of  processes,  and  a  new 
mechanism  of  the  hydraulic  functions.  The  ductus  venosus,  the 
foramen  ovale,  and  the  ductus  arteriosus  are  superseded  in  their 
functions,  and  must  be  speedily  closed  and  obliterated,  in  order 
to  give  place  to  new  courses  of  circulation  and  a  new  order  of 
functions. 

854.  Besides  these  changes,  which,  being  consequent  on  the 
sudden  exercise  of  the  new  function  of  respiration,  are  immediate, 
the  whole  organization  rapidly  conforms  itself  to  the  great  altera- 
tion of  the  circumstances  in  which  it  is  now  placed.    As  the  growth 


CHANGES    IN    THE    ANIMAL    ECONOMY.  357 

of  the  fcetus  had  been  progressively  becoming  more  and  more 
rapid  in  proportion  as  the  term  approached  when  it  was  to  be 
ushered  into  the  world;  so,  on  the  other  hand,  the  growth  of  the 
body  is  greatest  in  the  earliest  periods  of  its  extra-uterine  life,  and 
becomes  more  and  more  slow  in  proportion  as  it  advances  to  the 
full  dimensions  it  is  destined  to  attain.  The  principal  anatomical 
changes  which  follow  birth,  besides  those  already  stated,  are  the 
gradual  obliteration  of  the  thymus  gland,  and  of  the  renal  capsules. 

855.  The  natural  term  of  lactation  is  succeeded  by  that  of 
teething ;  the  first  set  of  teeth,  or  the  milk  teeth,  being  furnished 
by  nature  as  temporary  structures,  until  instruments  of  greater 
dimensions  can  be  constructed  in  the  enlarged  jaws.  The  appear- 
ance of  the  teeth  is  an  intimation  that  the  organs  of  assimilation 
are  prepared  for  the  digestion  of  soUd  food ;  and  that  the  proper 
period  for  weaning  is  arrived. 

856.  From  this  period  an  accurate  observer  may  perceive  that 
the  intellectual  education  keeps  pace  with  the  physical ;  whilst 
the  active  exercise  of  the  limbs  consolidates  the  bones,  and  gives 
firmness  to  the  muscles,  that  of  the  senses  is  continually  adding 
to  the  store  of  ideas,  and  calling  forth  the  latent  powers  of  the 
understanding.  The  moral  faculties  are  developed  much  earlier 
than  is  generally  imagined;  and  the  future  character  of  the  indi- ■ 
vidual  often  receives  a  permanent  impress  from  the  events  of 
infancy.  No  one  can  have  watched  its  varying  aspect  at  this 
tender  age,  without  recognising  how  early  affections  are  called 
forth  towards  its  protector  and  fosterer  ;  how  quick  is  the  distinc- 
tion it  makes  between  kind  and  unkind  treatment,  and  how  keen 
is  its  sense  of  the  least  injustice  which  it  may  have  either  to  bear 
or  to  witness. 

857.  To  the  periods  of  infancy  and  childhood  succeeds  that  of 
puberty,  which  we  have  seen  is  attended  in  either  sex  with  re- 
markable changes,  both  physical  and  moral.  During  the  period 
of  increase  the  power  of  assimilation  are  in  full  activity  in  fur- 
nishing a  sufficiency  of  materials  for  growth;  the  circulation  is 
vigorously  employed  in  applying  them  to  that  purpose ;  and  the 
supply  is  even  more  abundant  than  the  consumption.  When, 
however,  the  fabric  has  attained  its  prescribed  dimensions,  the 
total  quantity  of  nourishment  furnished  and  expended  being  nearly 
balanced,  the  vital  powei's  are  chiefly  exerted  in  consolidating 
and  perfecting  the  organization  of  every  part,  and  qualifying  them 
for  the  continued  exercise,  during  a  long  succession  of  years,  of 
those  functions  of  which  we  have  given  the  history  in  the  pre- 
ceding part  of  this  treatise. 

858.  But,  in  the  mean  time,  the  process  of  consolidation  begun 
from  the  earliest  period  of  development,  is  still  advancing,  and  is 
producing  in  the  fluids  both  greater  thickness,  and  a  diminution 
of  their  total  quantity.     By   the   gradual   conversion  of  their 


358  CHANGES    IN    THE    ANIMAL    ECONOMY. 

\ 

gelatin  into  albumen,  all  the  textures  acquire  increasing  solidity; 
the  cellular  substance  becomes  firmer  and  more  condensed,  and 
the  solid  structures  more  rigid  and  inelastic.  The  contractile  power 
of  the  muscles  is  also  impaired  ;  and  the  limbs  no  longer  retain 
the  elastic  spring  of  youth.  All  these  progressive  modifications 
of  structure  tend  slowly,  but  inevitably,  to  disqualify  the  organs 
for  the  due  performance  of  their  functions.  Their  vascularity 
gradually  diminishes ;  for  a  large  proportion  of  the  arteries  which 
had  been  actively  employed  in  building  the  fabric,  being  now 
thrown  out  of  employment,  contract,  and,  becoming  impervious, 
disappear.  The  parts  of  the  body,  having  acquired  greater  rigi- 
dity, oppose  a  gradually  increasing  resistance  to  the  propelling 
force  of  the  heart,  which  is  itself,  in  common  with  all  the  other 
vital  powers,  slowly  diminishing.  The  absorbents  are  now  active 
in  removing  the  parts  which  have  become  useless  or  superfluous. 
Old  age  steals  on  by  slow  and  imperceptible  degrees,  which,  even 
when  obvious  to  others,  are  unknown  to  ourselves.  But  nature 
kindly  smooths  the  path  along  which  we  descend  the  vale  of 
years,  and  conducts  us  by  easy  stages  to  our  destined  place  of 
repose.  When  death  is  the  simple  consequence  of  old  age,  we 
may  perceive  that  the  extinction  of  the  powers  of  life  observe 
an  order  the  reverse  of  that  which  was  followed  in  their  evolu- 
tion. The  sensorial  functions,  which  were  the  last  perfected,  are 
the  first  which  decay;  and  their  decline  is  found  to  commence 
with  those  mental  faculties  more  immediately  dependent  on  the 
physical  conditions  of  the  sensorium,  and  more  especially  with 
the  memory,  which  is  often  much  impaired  whilst  the  judgment 
remains  in  vigour.  The  heart,  the  pulsations  of  which  gave  the 
first  indications  of  life  in  the  embryo,  generally  retains  its  vitality 
longer  than  any  other  organ;  but  its  powers  being  dependent  on 
the  constant  oxidation  of  the  blood  in  the  lungs,  cannot  survive 
the  interruption  of  this  function,  and  on  the  heart  ceasing  to 
throb,  the  death  of  every  part  of  th6  system  may  then  be  consi- 
dered as  complete.* 

"*  For  more  ample  details  on  the  subject  of  the  changes  which  take  place 
in  the  progress  of  age,  see  the  article  Age  in  the  Cyclopaedia  of  Practical 
Medicine,  and  also  the  chapter  on  the  Decline  of  the  System  in  the  Bridge- 
water  Treatise  on  Animal  and  Vegetable  Physiology,  vol.  ii.  p.  619.  [Amer. 
edit.  ii.  433.] 


TEMPERAMENTS.  359 


CHAPTER    XXI. 

TEMPERAMENTS. 

859.  In  the  natural  and  healthy  condition  of  the  system,  all  its 
functions  are  nicely  adjusted  and  proportioned  to  each  other,  so 
as  to  produce  the  most  perfect  harmony.  Yet  within  the  limits 
of  health  variations  are  admissible  in  this  balance  of  functions, 
according  as  some  predominate  over  others  in  regard  to  energy 
and  activity ;  or  rather,  according  as  there  prevails  a  tendency 
to  such  predominance,  which,  though  it  does  not  actually  overset, 
may  yet  endanger  the  preservation  of  that  balance  which  consti- 
tutes health,  and  may  thus  give  at  least  a  proneness  to  disease. 
This  peculiar  state  of  the  system,  depending  on  the  relation  be- 
tween its  different  capacities  and  functions,  by  whit;h  it  acquires 
a  tendency  to  certain  modes  of  action,  is  called  Temperament. 

860.  Much  attention  was  paid  by  the  ancients  to  the  subject  of 
temperaments ;  and  the  nomenclature  they  established  to  express 
the  various  combinations  of  peculiarities  in  the  constitution,  cor- 
responding with  the  definition  above  given,  has  continued  in 
general  use  even  to  the  present  day.  They  described  four  tem- 
peraments, corresponding  to  the  four  qualities  of  hot,  cold,  moist, 
and  dry,  ascribed  to  the  human  frame  by  Hippocrates,  and  which 
were  supposed  to  confer  the  specific  characters  to  the  four  ingre- 
dients of  which  the  blood  was  thought  to  be  composed  ;  namely, 
the  red  part,  the  phlegm,  the  yellow,  and  the  black  bile  respect- 
ively; and  hence  were  derived  the  names  of  the  sanguine,  the 
phlegmatic,  the  choleric,  and  the  melancholic  temperaments,  as 
indicating  an  excess  of  each  of  these  principles. 

861.  In  modern  times  the  ancient  doctrine  of  temperaments 
was  adapted  to  the  humoral  pathology,  by  which  all  the  devia- 
tions from  the  standard  of  health  were  attempted  to  be  explained. 
Boerhaave,  reasoning  on  these  principles,  and  considering  the 
several  temperaments  as  being  formed  by  diflerent, combinations 
of  the  four  cardinal  qualities,  increased  their  number  to  the  eight 
following  :  namely,  the  warm,  cold,  moist,  dry,  bilious,  sanguine, 
phlegmatic,  and  atrabilious.  Darwin,  endeavouring  to  found  his 
doctrine  of  temperaments  on  varieties  in  the  vital  actions  of  the 
system,  which  he  had  classified  as  referring  to  the  four  heads  of 
irritation,  sensation,-  volition,  and  association,  formed  four  tem- 
peraments in  conformity  with  this  arrangement,  in  which  these 
functions  were  conceived  respectively  to  predominate. 

862.  Most  of  the  modern  physiologists,  however,  following  the 


360  TEMPERAMENTS. 

example  of  Cullen,  havp  adopted  the  four  temperaments  of  Hip- 
pocrates, which  are  characterized  by  the  following  peculiarities: 

863.  The  Sanguine  temperament  is  distinguished  by  a  full 
habit  and  relaxed  frame  of  body ;  by  a  greater  vascularity,  soft- 
ness and  delicacy  of  skin,  in  which  the  veins  are  of  considerable 
size,  and  are  particularly  conspicuous  by  their  blue  colour,  as 
seen  through  the  thin  layers  of  the  skin.  The  surface  of  the  body 
generally,  and  more  especially  the  face,  exhibits  a  florid  and 
ruddy  colour.  The  hair  is  generally  of  a  light  brovi^n  ;  but  has 
often  a  yellow,  and  sometimes  a  reddish  hue.  Persons  endowed 
with  a  sanguine  temperament  are  acutely  sensitive,  and  highly 
irritable :  their  pulse  is  frequent,  indicating  the  general  rapidity 
and  energy  of  the  circulation.  Both  the  secretions  and  excre- 
tions are  abundant,  and  little  liable  to  obstruction.  The  disposi- 
tion is  free  and  open ;  the  temper  cheerful,  and  rather  disposed 
to  levity. 

864.  A.  remarkable  contrast  to  the  temperament  just  described 
is  presented  by  the  melancholic  temperament,  which  is  marked 
by  a  firm  and  robust  frame,  and  a  spare  habit  of  body ;  by  an 
integument  of  sr-eater  thickness,  and  of  a  brown  and  swarthy 
hue ;  and  by  an  abundance  of  dark  or  black  hair,  which  being 
particularly  conspicuous  in  the  eye-brows  and  beard,  and  being 
conjoined  with  a  black  colour  of  the  iris,  imparts  to  the  counten- 
ance a  stern  and  sombre  aspect.  In  persons  endowed  with  tkis 
temperament  the  pulse  is  habitually  slower  than  the  average 
condition  ;  the  blood  is  thicker  and  more  sluggish  ;  the  secretions 
and  the  excretions  are  less  copious,  and  more  apt  to  be  morbidly 
deficient  tjian  with  the  generality  of  men.  The  nervoiis  system 
is,  on  the  whole,  less  sensitive  and  excitable ;  but  the  mind,  al- 
though not  readily  moved,  when  once  set  in  motion,  is  remark- 
ably retentive  of  its  impressions,  and  tenacious  of  its  purposes  ; 
persevering  and  indefatigable  in  action,  ardent  and  constant  in 
its  affections ;  possessing  great  capacity  of  understanding,  with 
a  fondness  for  contemplation,  and  for  speculative  inquiries  de- 
manding profound  thought.  The  temper  is  naturally  grave,  and 
often  gloomy  ;  the  fancy  imaginative,  and  of  a  poetic  turn,  but 
tinctured  with  melancholy,  and  betraying  a  proclivity  to  mad- 
ness ;  when  happily  tempered,  it  exhibits  that  fortunate  combina- 
tion of  genius  and  industry  from  which  have  resulted  the  noblest 
achievements  of  the  human  intellect. 

865.  The  Choleric  temperament  would  seem  to  occupy  a  place 
intermediate  between  the  two  former,  as  partaking  of  some  of 
the  qualities  of  both.  The  frame  is  more  relaxed,  the  senses 
more  excitable,  and  the  mind  more  irascible  than  in  the  melan- 
cholic temperament.  The  complexion  is  less  ruddy  than  in  the 
sanguine  temperament,  and  the  pulse  stronger  and  more  frequent; 
the  secretions  are  more  copious,  and  the  skin  fairer  and  less 
hairy  than  in  the  melanchohc  temperament. 


PHLEGMATIC    TEMPERAMENT.  361 

866.  The  Phlegmatic  temperament  is  denoted  by  a  relaxed 
and  feeble  frame,  prone  to  obesity ;  a  pallid  complexion,  a  smooth 
integument,  with  but  few  hairs,  that  on  the  head  being  of  a  light 
colour.  The  circulation  generally  is  languid,  the  pulse  slow  and 
weak,  the  blood-vessels  less  capacious,  the  fluids  more  bland  and 
watery.  The  functions  of  digestion,  secretion,  and  excretion,  are 
performed  slowly,  and  are  liable  to  frequent  impediments.  The 
mind  is  dull,  sluggish,  disposed  to  indulge  in  sleep;  not  easily 
moved,  timid,  inclined  to  fear,  and  prone  to  avarice. 

867.  Dr.  Gregory  has  added  to  these  four  temperaments  a  fifth, 
which  he  denominates  the  nervous  temperament,  and  which  owes 
its  peculiarities  to  the  sensibility  of  the  nervous  system  existing 
in  an  undue  proportion  to  the  conti  actllity  of  the  muscles  ;  con- 
joining the  qualities  of  excitability  and  of  debility.  Such  an  union 
of  qualities,  however,  is  compatible  with  the  characteristics  of 
other  temperaments,  but  occurs  more  commonly  in  the  sanguine, 
whether  existing  in  its  purest  form,  or  blended  with  the  phleg- 
matic ;  and  it  is  found  exemplified  chiefly  among  those  whose 
occupations  are  sedentary,  and  who  lead  a  life  of  ease  and 
hjxury. 

868.  These  several  temperaments  are  found  variously  modified 
by  occasional  intermixture  in  dilTerent  degrees  with  one  another. 
Thus,  the  phlegmatic  is  often  conjoined  with  the  sanguine,  and 
sometimes  with  the  melancholic  temperaments  ;  and  observation 
will  readily  suggest  examples  of  other  similar  combinations. 
The  predominance  of  each  of  these  temperaments  varies  at  dif- 
ferent periods  of  life.  At  an  early  age  the  system  inclines  more 
to  the  sanguine;  in  middle  life,  to  the  choleric  ;  and  at  a  more 
advanced  age,  to  the  melancholic  temperament.  They  admit 
also  of  being  variously  influenced  and  modified  by  climate, 
habits,  and  education;  and  accordingly  each  is  found  to  prevail 
amongst  particular  tribes  and  nations,  and  in  particular  regions 
of  the  globe.* 

*  [The  whole  doctrine  of  the  temperaments  is  more  specious  perhaps  than  real. 
The  very  foundation,  Indeed,  of  the  predominance  of  particular  humors, 
systems,  or  apparatuses  is  wholly  supposititious.  It  is  obvious,  too,  that  the 
physical  characteristics  described,  can  in  no  wise  apply  to  the  coloured  races. 
There  is  doubtless  a  difference  in  the  organization  or  constitution  of  diiferent 
individuals,  but  this  is  but  imperfectly  explained  by  the  doctrine  in  question. 
M.  Georget,  indeed  (Physiologie  de  Systeme  nerveux,  Paris,  1821),  regards  it 
as  a  superstition  connected  with  the  humoral  pathology,  and  he  believes  that 
the  brain,  alone  amongst  the  organs,  has  the  power,  by  reason  of  its  pre- 
dominance or  superiority,  to  modify  the  whole  economy.] 


31 


VARIETIES   OF    THE    HUMAN    SPECIES. 

CHAPTER   XXII. 

VARIETIES  OF  THE  HUMAN  SPECIES. 

869.  It  has  been  a  question  much  agitated  amongst  naturahsts, 
"whether  the  differences  observable  in  the  complexion,  features, 
and  the  intellectual  and  moral  endowments  of  different  tribes  and 
nations  which  are  found  scattered  over  the  surface  of  the  globe 
are  sufficiently  great  to  mark  an  original  diversity  of  species,  or 
whether  they  correspond  merely  to  the  character  of  varieties 
taking  place  in  a  single  original  race,  analogous  to  those  we  be- 
behold  in  many  domesticated  animals,  such  as  the  dog,  the  horse, 
and  the  sheep,  and  therefore  affording  no  objection  to  the  hypo- 
thesis that  every  individual  composing  the  human  race  belongs 
really  to  one  and  the  same  species.  To  Blumenbach  belongs  the 
merit  of  being  the  first  who  entered  w-ith  a  philosophical  spirit 
into  the  investigation  of  this  great  problem.  The  generally  pre- 
vaihng  opinion  at  present  is,  that  all  mankind  are  the  descendants 
of  the  same  original  stock;  and  are  therefore  to  be  considered  as 
members  of  the  same  family. 

870.  It  is  a  matter  of  considerable  difficulty  to  establish  an 
accurate  classification  of  the  different  varieties  into  which  the 
human  race  should  be  divided.  Blumenbach,  who,  from  having 
devoted  to  it  much  labour  and  attention,  is  justly  considered  as 
the  highest  authority  on  this  subject,  has  fixed  the  number  of 
these  varieties  at  five ;  though,  as  Mr.  Lawrence  observes,  these 
five  races  ought  perhaps  rather  be  considered  as  principal  divisions, 
each  of  them  including  several  subordinate  varieties.  M.  Bory  de 
St.  Vincent,  in  his  Treatise  on  Man,  extends  the  number  of  primitive 
varieties  to  fifteen.  Cuvier,  on  the  other  hand,  is  inclined  to  refer 
all  the  varieties  in  the  race  to  three  principal  heads,  considering 
the  others  as  merely  modifications  of  these. 

871.  The  five  varieties  which  Blumenbach  has  pointed  out 
are  designated  by  the  terms  Caucasian,  Mongolian,  Ethiopian, 
American,  and  Malay.  He  regards  the  Caucasian  race  as  the 
primitive  stock,  or  as  the  standard  and  type  of  the  rest.  It 
appears,  indeed,  to  occupy  an  intermediate  place  between  the 
Mongolian  race,  on  the  one  side,  and  the  Ethiopian  on  the  other 
which  latter  races  are  the  most  wddely  different  from  each  other. 
The  American  variety  has  been  considered  as  intermediate 
between  the  Caucasian  and  the  Mongolian ;  and  the  Malay 
race  as  intermediate  between  the  Caucasian  and  the  Ethiopian. 
The  various  intermixtures  which  have  taken  place  between  these 


ETHIOPIAN    RACE.  363 

several  races,  in  different  parts  of  the  world,  render  it  very 
difficult,  at  the  present  day,  to  draw  those  precise  Hnes  of  dis- 
tinction which  have  probaljly,  in  remoter  times,  characterized  the 
primitive  races  now  enumerated.  Thus,  in  Asia,  we  find  con- 
siderable mixtures  of  the  Caucasian  with  the  Mongolian  races; 
whilst  in  Africa,  the  Caucasian  race  has  in  various  instances  been 
blended  with  the  Ethiopian.  The  following  are  the  circumstances 
by  which  these  several  varieties  are  characterized  : — 

872.  L  The  Caucasian  races  are  distinguished  by  the  general 
whiteness  of  the  skin  ;  the  fairer  complexions  exhibiting  a  roseate 
tint,  particularly  conspicuous  in  the  cheeks,  and  derived  from  the 
abundance  of  blood  circulating  in  the  vessels,  and  the  darker 
races  inclining  to  a  brown,  and  by  the  abundance  and  softness 
of  the  hair,  which  is  either  black,  or  of  a  lighter  chestnut  colour, 
occasionally  inclining  to  red.  The  cranium  is  large  and  oval, 
and  developed  especially  about  the  forehead  ;  the  face  compara- 
tively small,  and  falling  perpendicularly  underneath  the  forehead 
The  features  are  distinct  from  each  other ;  the  nose  narrow,  and 
frequently  aquiline ;  the  mouth  small ;  the  front  teeth  in  both  jaws 
have  a  perpendicular  direction ;  the  lips,  particularly  the  lower 
one,  are  gently  turned  outwards  ;  the  chin  is  full  and  rounded, 
and  the  general  contour  of  the  face  has  an  oval  form,  and  is 
broader  in  the  upper  than  in  the  lower  portion.  This  is  the  race 
in  which  the  moral  and  intellectual  energies  of  man  have  risen 
to  a  higher  degree  of  excellence  than  in  any  other;  and  it  is  the 
race  which  has  at  all  times  been  the  most  susceptible  of  cultiva- 
tion and  improvement.  The  hope  may  indeed  be  entertained 
that  it  is  yet  far  from  having  arrived  at  the  highest  point  in  these 
respects  which  it  is  destined  to  attain. 

873.  2.  The  Mongolian  races  are  characterized  by  a  com- 
plexion approaching  to  an  olive  colour  ;  the  eyes  being  black  ;  the 
hair  also  black,  strong,  and  straight;  the  beard  thin  and  scanty; 
and  the  head  of  a  form  somewhat  square ;  the  cheek  bones  large 
and  prominent;  the  forehead  low;  the  face  broad;  the  features 
flattened,  and  running  together;  the  nose  small  and  flat;  the 
aperture  of  the  eyelids  narrow,  and  the  orbits  situate  obliquely; 
the  lips  thick;  the  chin  slightly  projecting;  the  ears  large.  The 
stature  of  most  of  the  nations  belonging  to  this  race  is,  in  general, 
inferior  to  that  of  Europeans. 

874.  3.  The  Ethiopian  or  negro  race  is  marked  by  the  lateral 
compression  of  the  skull,  which  is  elongated  forwards  ;  by  the 
prominence  of  the  cheek  bones,  the  narrowness  and  projection 
of  the  jaws,  and  the  recession  of  the  chin.  The  forehead  is  low, 
and  very  slanting;  the  eyes  prominent;  the  nose  broad,  thick, 
and  flat ;  the  lips,  the  upper  one  especially,  thick ;  the  upper 
front  teeth  are  obhque  ;  the  hair  black  and  woolly  ;  the  legs  are 


364  VARIETIES   OF    THE    HUMAN    SPECIES. 

long  and  slender ;  the  calf  especially  is  small,  and  the  knees  are 
bent  inwards ;  the  arms  are  longer  than  in  the  other  races. 

875.  4.  The  Aboriginal  American  race  is  remarkable  for  the 
red  colour  of  the  skin,  the  strong  and  straight  black  hair,  the 
scanty  beard,  and  low  forehead,  the  deeply  sunk  eyes,  and  the 
round  and  prominent  cheek  bones.  The  mouth  is  large,  the  lips 
thick,  and  the  face  in  general  broad  and  square;  characters 
which  assimilate  this  race  with  the  Mongolian,  from  which,  how- 
ever, it  is  sufficiently  distinguished  by  the  colour  of  the  skin,  and 
the  projection  of  the  features,  especially  of  the  nose. 

876.  5.  The  Malay  variety  of  the  human  species  varies  consi- 
derably in  the  colour  of  the  skin,  from  a  light  tawny  brown,  to 
one  approaching  to  black.  The  head  is  narrow ;  the  bones  of 
the  face  are  large  and  prominent ;  the  m.outh  large ;  the  nose 
full  and  broad  at  the  point.  The  hair  is  black,  and  more  or  less 
curling. 

The  following  account  of  the  filiation  of  the  different  races, 
and  of  their  distribution  over  the  globe,  is  given  by  Cuvier. 

877.  The  Caucasian  race  has  been  so  named  from  its  presumed 
origin  in  the  western  part  of  Asia,  in  the  neighbourhood  of  the 
Caucasian  chain  of  mountains,  which  are  situate  between  the 
Caspian  and  the  Black  Seas ;  whence  it  has  spread  as  from  a 
centre  to  the  adjacent  parts  .of  the  Asiatic,  European,  and  African 
continents.  The  present  inhabitants  of  these  regions,  namely,  the 
Circassians  and  the  Georgians,  are  reputed  to  be  still  the  hand- 
somest race  on  earth.  The  principal  ramifications  from  the 
primitive  stock,  may  be  most  satisfactorily  traced  by  following 
the  analogies  of  the  languages  of  the  nations  which  have  pro- 
ceeded from  it.  Thus,  the  Armenian,  or  Syrian  branch,  pro- 
ceeded southwards,  and  gave  rise  to  the  Assyrian  and  Chaldean 
nations  ;  and  also  to  the  Arabians,  who,  after  the  era  of  Mahomet, 
aspired  to  the  empire  of  the  world.  The  Phoenicians,  Jews,  and 
Abyssinians  may  be  regarded  as  Arab  colonies,  to  which  class 
also  the  Egyptians  may  probably  be  referred. 

878.  The  branch  giving  origin  to  the  Indian,  Germanic,  and 
Pelasgic  tribes  was  far  more  widely  spread,  and  became  subdi- 
vided at  a  much  remoter  period  of  antiquity.  Amongst  the  four 
principal  languages  which  prevailed  among  the  nations  com- 
posing these  races,  namely,  the  Sanscrit,  tlie  ancient  Pelasgic, 
the  Gothic  or  Teutonic,  and  the  Sclavonic,  we  may  trace  the 
most  multiplied  affinities.  The  primitive  Sanscrit  is  still  pre- 
served as  the  sacred  language  of  the  Hindus,  and  is  the  model  on 
which  all  the  existing  languages  of  Hindustan  have  been  formed. 
The  Pelasgic  is  the  primitive  source  of  the  Greek,  of  the  Latin, 
and  of  many  other  tongues  now  extinct,  but  from  which  most  of 
the  present  languages  of  the  south  of  Europe  have  been  derived. 
The  Teutonic  has  given  rise  to  the  languages  of  the  northern  and 


MONGOLIAN    RACE.  365 

the  western  nations  of  Europe,  such  as  the  German,  the  Dutch,  the 

English,  the  Danish,  the  Swedish,  together  with  their  various 
dialects.  From  the  Sclavonic  tongue  are  derived  those  of  the 
north-east  of  Europe,  namely,  the  Russ,  Polish,  the  Bohemian, 
and  the  Vandean. 

879.  It  is  amongst  this  latter  extensive  race  that  philosophy, 
sciences,  and  the  arts,  have  been  most  assiduously  cherished,  and 
have  been  carried  to  the  highest  states  of  perfection.  This  race 
had,  in  Europe,  been  preceded  by  the  Celtic  tribes,  which  origi- 
nally came  from  the  north,  and  were  formerly  widely  spread, 
but  which  are  now  confined  to  very  narrow  spaces  in  the  west 
of  Europe  and  Africa,  and  are  nearly  effaced  by  continued  in- 
termixture with  the  numerous  races  which  have  supplanted 
them. 

880.  The  ancient  Persians  have  a  similar  origin  with  the 
Indians;  and  their  descendants  at  the  present  time,  bear  the 
strongest  marks  of  affinity  to  the  modern  European  nations. 

881.  The  Scythian  or  Tartaric  branch  first  directed  itself 
towards  the  north  and  north-east,  and  composed  the  wandering 
tribes  which  traversed  the  immense  plains  of  Tartary.  In  later 
times,  become  more  numerous,  they  returned  to  spread  devasta- 
tion amongst  the  flourishing  establishments  of  their  more  civilized 
brethren.  The  irruptions  of  the  Scythians  in  Upper  Asia,  of  the 
Parthians,  who  overthrew  the  domination  of  the  Greeks  and  Ro- 
mans in  those  regions;  of  the  Turks,  who  destroyed  that  of  the 
Arabs,  and  reduced  to  subjection  the  miserable  remnant  of  the 
Greek  nations  in  Europe ;  all  proceeded  from  the  overflowings  of 
the  northern  swarms  from  this  common  race.  The  Finlanders 
and  the  Hungarians,  which  belong  to  this  race,  may  be  regarded 
as  stragglers  from  these  swarms,  amidst  Sclavonic  and  Teutonic 
tribes.  On  the  northern  and  eastern  coasts  of  the  Caspian  Sea, 
the  original  cradle  of  these  races,  there  are  still  found  tribes  which 
liave  the  same  common  origin  with  the  former,  and  which  speak 
a  similar  language ;  but  they  are  variously  intermixed  with  a 
great  number  of  other  smaller  tribes,  differing  from  them  both  in 
language  and  in  origin. 

882.  The  Tartarian  tribes  have  remained  more  free  from 
mixture,  along  the  whole  of  that  extensive  tract  whence  they  long 
defied  the  power  of  Russia,  but  to  which  they  have  at  length  been 
forced  to  submit ;  namely,  from  the  mouths  of  the  Danube,  to  the 
countries  beyond  those  of  the  Irtish.  But  the  conquests  of  the 
Mongols  have  led  to  considerable  blending  of  the  two  races 
amongst  the  Tartarian  nations. 

883.  The  Mongolian  race  inhabits  the  remoter  regions  of  Asia, 
extending  from  the  eastern  parts  of  the  continent,  where  the 
Tartar  branch  of  the  Caucasian  race  terminates,  to  the  Eastern 
Ocean.     The  different  branches  of  this  MongoUan  race,  such  as 

31* 


366  VARIETIES   OF    THE    liUMAN    SPECIES. 

the  Calmuc  Tartars,  and  the  Kalkas,  have  no  settled  residence, 
but  are  -wandering  tribes  over  the  extensive  deserts  of  Eastern  Asia. 
Thrice  have  their  ancestors  carried  far  and  wide  the  terror  of 
their  arms ;  first,  under  Attila  ;  next  under  Genghis  Khan ;  and, 
lastly,  under  Tamerlane.  The  Chinese  are  an  ancient  branch  of 
this  family,  which  was  very  early  trained  to  a  high  degree  of 
civilization  ;  at  a  period,  indeed,  apparently  more  remote  than 
that  to  which  our  most  ancient  histories  extend.  The  Manchew 
Tartars,  who  have  recently  achieved  the  conquest  of  China,  are 
a  third  branch  of  the  same  Mongolian  race.  The  Japanese,  the 
Coreans,  and  almost  all  the  hordes  which  extend  to  the  north-east 
of  Siberia,  under  the  dominion  of  Russia,  belong  also  to  the  same 
division  of  the  human  species. 

The  original  seat  of  this  widely-spread  race  appears  to  be  the 
chain  of  the  Altai  mountains,  the  central  ridge  of  Asia ;  in  the 
same  way  that  the  race  to  which  we  belong  was  derived  from 
the  inhabitants  of  mount  Caucasus ;  but  it  is  quite  impossible  to 
unravel  the  complicated  filiation  of  these  various  tribes.  The 
history  of  these  wandering  people  is  as  evanescent  as  their  estab- 
lishments ;  and  even  that  of  the  Chinese,  confined  as  it  is  to  the 
limits  of  their  empire,  supplies  only  brief  and  unconnected  notices 
of  the  surrounding  nations.  The  afiinities  of  their  languages  are 
too  imperfectly  known  to  afford  any  clue  for  our  guidance  in  this 
mighty  labyrinth. 

884.  The  languages  of  the  north  of  the  Indian  peninsula,  beyond 
the  Ganges,  as  well  as  that  of  Thibet,  have  som.e  relations  Vk'ith 
the  Chinese  language ;  at  least  they  resemble  it  in  their  monosyl- 
labic structure.  There  is  also  a  general  resemblance  of  features 
amongst  all  these  Mongolian  tribes.  But  the  southern  division  of 
the  same  peninsula  is  inhabited  by  a  diflerent  race,  namely, 
Malays,  distinguished  from  the  former  by  their  greater  symmetry 
of  form,  and  by  a  peculiar  language.  This  race  is  spread  over 
the  coasts  and  islands  of  the  Indian  Archipelago,  as  well  as  those 
of  the  Southern  Pacific.  In  the  largest  of  the  Indian  Islands, 
however,  we  meet  with  a  much  more  barbarous  race  of  men  with 
dark  Avoolly  hair,  with  black  skins,  and  with  the  negro  features, 
and  savage  and  ferocious  in  their  dispositions.  They  are  known 
by  the  name  of  Papuans,  and  are  principally  met  with  in  the 
Islands  of  New  Guinea,  and  the  New  Hebrides.  It  has  been 
conjectured  that  this  singular  tribe  was  descended  from  negroes 
accidentally  cast  on  the  shores  of  these  remote  islands. 

885.  The  inhabitants  of  the  northernmost  regions  both  of  the 
old  and  new  continent,  comprising  the  Samoiedes,  the  Laplanders, 
and  the  Esquimaux,  possess  many  peculiar  features,  and  have  been 
classed  by  some  naturalists  under  the  Mongolian  races,  but  are 
considered  by  others  as  degenerated  scions  from  the  Scythian 
and  Tartaric  branches  of  the  Caucasian  race. 


UNITY    OF    SPECIES.  367 

886.  The  aboriginal  American  Indians  have  never  been  satis- 
factorily assimilated  to  any  one  of  the  races  of  the  ancient  con- 
tinent ;  yet  they  scarcely  possess  any  precise  or  well  marked 
distinctive  characters,  which  may  entitle  them  to  be  regarded  as 
one  of  the  primitive  races  of  mankind.  The  copper  hue  of  their 
skin  is  certainly  not  of  itself  sufficient  to  establish  such  a  distinc- 
tion. Their  dark  hair  and  scanty  beard  would  incline  us  to  refer 
them  to  the  Mongolian  race,  were  it  not  that  their  well-defined 
features,  and  prominent  nose,  are  opposed  to  such  a  classification. 
Their  languages  are  as  diversified  as  their  tribes  are  numerous; 
and  no  analogy  has  yet  been  traced  either  amongst  o«e  another, 
or  with  any  of  those  of  the  old  world. 

887.  The  analogy  of  what  we  observe  in  the  inferior  animals, 
affords  the  strongest  grounds  for  believing  that  natural  causes 
are  perfectly  adequate  to  explain  the  diversities  which  occur  in 
the  several  varieties  of  the  hun)an  race,  on  the  supposition  of  their 
having  originated  from  a  common  stock.     The  variations  in  size, 
colour,  and  even  forms,  which  take  place  amongst  difierent  kinds 
of  dogs,  characters  which  are  transmitted  from  the  parent  to  the 
otfspring  with  as  much  constancy  as   those  of  the  human  race, 
are  no  less  considerable  than  the  difl^erences  observable  between 
the  European  and  the  negro,  and  yet  are  admitted  by  naturalists 
to  be  perfectly  compatible  with  the  unity  of  the  species,  and  with 
a  community  of  source.     Of  the  causes  which  originally  produced 
the  peculiarities  in  the  several  varieties  of  the  race,  and  which 
have  become  permanent,  we  can  have   no  certain   knowledge; 
nor  can  we  even  supply  the  want  of  precise  information  by  any 
rational  conjecture.     The  common  hypothesis  which  ascribes  the 
black  colour  of  the  negro  to  the  more  powerful  influence  of  the 
solar  rays  in  tropical  climates,  will  not  bear  the  test  of  close 
examination  ;  no  permanent  effect  of  that  kind  having  ever  been 
produced  by  the  same  cause  operating  for  any  length  of  time  on 
the    complexion  of   Europeans.     Difierent   opinions    have  been 
entertained  with  regard  to  the  natural  and  original  complexion 
of  the  human  race.     Dr.  Prichard  contends  that  it  was  black, 
and  that  the  Ethiopian  form  was  the  primitive  type  of  the  race; 
the  successive  changes  produced  being  that  from  the  imperfect 
to  the  more  perfect  form,  and  from   barbarism  to   refinement ; 
terminating  at  length  in  the  Caucasian  race,  in  which  it  has  at- 
tained the  greatest  state  of  improvement  compatible  with  its  nature^ 
accompanied  by  the  highest  degree  of  capability  of  civilization, 
and  of  intellectual  and  moral  excellence.* 

888.  In  opposition  to  the  doctrine  of  the  unity  of  species  in  all 
human  races,  it  has  been  contended  by  Rudolphi,  Virey,  Des- 

*  See  his  Researches  on  the  Physical  History  of  Mankind,     Third  edition. 
London,  1806. 


3*68  COMPARATIVE    PHYSIOLOGY. 

moulins,  Bory  St.  Vincent,  and  others,  in  the  most  positive  man- 
ner, that  these  races  were  originally  different.  The  arguments 
on  each  side  of  the  question  are  fully  discussed  in  the  work  of 
Dr.  Prichard  referred  to. 


CHAPTER    XXIIl. 


COMPARATIVE    PHYSIOLOGY. 


889.  We  purpose,  in  giving  an  account  of  the  most  important 
facts  relating  to  the  physiology  of  the  animal  creation,  to  take  as 
the  standard  of  comparison  the  mode  in  which  the  functions  of 
the  human  body  are  conducted.  The  history  we  have  given  of 
the  animal  economy  in  man  will  easily  enable  us  to  refer  all  the 
facts  relating  to  comparative  physiology  to  this  standard  type ; 
and  this  view  of  the  subject,  besides  the  interest  which  naturally 
attaches  to  it,  will  have  the  further  advantage  of  reflecting  light 
on  various  subjects  of  human  physiology,  which,  as  we  formerly 
remarked,  must  ever  receive  important  elucidation  from  a  com- 
parison with  that  of  the  lower  animals. 

890.  Conformably  with  this  design  we  shall  take  a  review  of 
the  different  divisions  of  the  animal  kingdom  ;  first  pointing  out 
the  general  characters  of  organization  and  of  function  which  are 
common  to  each  class  and  order  ;  and  noticing,  in  the  next  place, 
the  peculiarities  that  are  most  worthy  of  remark  in  the  several 
species  included  in  those  divisions.  By  thus  following  the  logical 
order  of  descending  from  generals  to  particulars,  we  shall  avoid 
the  numerous  repetitions  that  would  otherwise  be  requisite,  and 
comprise  in  the  smallest  space  the  greater  number  of  particular 
facts  relating  to  the  science.  \ 


Sect.  I. — Comparative  Physiology  of  Mammalia. 

1.  Peculiarities  in  the  Human  Conformation. 

891.  Since  man,  in  his  zoological  relations,  must  be  compre- 
hended in  the  class  mammaUa,  it  is  evident  that  the  general 
characters  of  this  class  must  consist  of  those  possessed  by  the 
human  species  in  common  with  quadrupeds,  and  even  with  the 
other  families  of  mammalia  still  farther  removed  from  man  in 
their  external  conformation.  Whilst  the  points  of  resemblancs 
are  so  numerous,  the  easiest  mode  of  instituting  a  comparison 


PECULIARITIES   OF    HUMAN    CONFORMATION.  369 

between  them  will  evidently  be  by  pointing  out,  not  the  features 
which  they  possess  in  common,  but  those  in  which  they  differ. 
We  shall  begin  then  with  an  account  of  the  peculiarities  which 
distinguish  the  human  structure  from  that  of  the  lower  animals, 
and  more  especially  from  that  of  the  quadrumanous  tribes,  which 
approach  the  nearest  to  him  in  their  conformation. 

892.  The  great  distinctive  features  which  characterize  the 
human  conformation,  as  compared  with  that  of  all  other  mam- 
malia, have  reference  to  the  superiority  of  his  intellectual  powers, 
and  to  his  maintenance  of  the  erect  position.  In  the  number 
and  excellence  of  his  mental  faculties,  and  in  his  capabilities  of 
improvement,  he  leaves  all  other  animals  behind  by^  an  immea- 
surable distance.  The  faculty  of  speech  is  a  consequence  of  this 
development  of  intellectual  power,  which  is  favoured,  indeed,  by 
the  conformation  of  the  larynx  ;  but  the  organization  requisite 
for  the  uttering  of  articulate  sounds  would  have  been  in  vain 
conferred  unless  it  had  been  placed  under  the  guidance  of  the 
mental  faculties ;  thus  to  the  parrot  the  gift  of  the  organs  of 
articulation,  without  the  mind  which  is  to  use  them  as  expressions 
of  thought,  becomes  a  comparatively  unprofitable  boon. 

893.  The  superiority  of  the  human  intellect  is  accompanied  by 
a  much  greater  development  of  the  cerebral  hemispheres  than  is 
found  in  any  other  animal.  Hence  also  the  great  magnitude  of 
the  cavity  in  which  it  is  contained,  together  with  that  part  of  the 
skull  which  protects  it,  when  compared  with  the  face,  which  is 
composed  of  the  organs  of  the  principal  senses,  and  of  the  appa- 
ratus for  mastication.  The  mass  of  the  brain  bears  also  a  large 
proportion  to  the  size  of  the  cerebral  nerves.  The  cerebellum  is 
entirely  covered  by  the  hemispheres  of  the  brain.  The  forehead 
in  man  is  particularly  distinguished  by  its  elevation,  and  the  beauty 
of  its  convex  arch.  The  shortness  of  the  lower  jaw,  and  the 
prominence  of  its  mental  portion,  are  particularly  remarkable. 
The  elephant  is  the  only  quadruped  in  which  the  lower  jaw  is 
equally  short  jn  proportion  to  the  size  of  the  head  ;  but  this 
animal  is  still  deficient  in  the  projection  of  its  lowest  point,  so 
that  the  possession  of  a  chin  seems  to  be  peculiar  to  the  human 
race. 

894.  In  every  particular  connected  v;ith  the  mechanism  of  the 
fabric,  man  enjoys  the  most  decided  advantage  over  those  mam- 
malia which  are  most  nearly  allied  to  him  in  their  physical  con- 
formation, Man  is  the  only  species  amongst  the  mammalia 
whose  body  can  maintain  itself  for  any  length  of  time  in  an  erect 
position,  and  in  whom  the  office  of  supporting  the  trunk  is  en- 
trusted solely  to  the  lower  extremities.  We  find  that  every  part 
of  the  osseous  fabric,  as  well  as  the  disposition  of  the  principal 
organs  of  sense,  are  in  obvious  conformity  with  this  design.  The 
lower  limbs,'  being  the  great  instruments  of  support  and  progres- 


370  COMPARATIVE    PHYSIOLOGY. 

sion,  are  larger,  and  of  greater  strength,  compared  with  the  body, 
than  in  most  quadrupeds,  the  only  exceptions  being  met  with 
among  those  which  are  formed  expressly  for  leaping,  as  the  hare, 
the  jerboa,  and  the  kangaroo.  In  the  monkey  tribes  the  lower 
limbs  are  comparatively  much  weaker  than  in  man;  and  in  other 
quadrupeds  the  disproportion  is  still  greater,  the  thigh  bone  being 
short,  and  almost  concealed  by  the  muscles  which  connect  it  with 
the  trunk  of  the  body,  whilst  the  rest  of  the  limb  is  very  slender, 
and  not  covered  by  any  considerable  mass  of  muscle.  In  man 
the  articular  surfaces  of  the  knee-joint  are  very  broad,  and  admit 
of  greater  extent  of  motion  than  in  quadrupeds,  and  the  two 
portions  of  ^he  limb  can  be  brought  into  the  same  straight  line, 
thus  constituting  firm  perpendicular  columns  of  support  for  the 
body.  The  long  neck  of  the  thigh  bone  allows  of  more  complete 
rotation  of  the  limb  at  the  hip-joint ;  and  this,  together  with  the 
greater  breadth  of  the  pelvis,  which  affords  an  ample  basis  for 
sustaining  the  trunk,  are  circumstances  peculiar  to  the  human 
frame.  The  heel  in  man  forms  a  greater  projection  than  in  other 
animals  ;  and  by  its  being  extended  so  as  to  touch  the  ground,  it 
forms,  as  we  have  seen,  one  of  the  points  of  support,  by  which,  in 
conjunction  wdth  the  toes,  a  much  larger  base  is  comprehended. 
The  muscles  which  raise  the  heel,  and  which  compose  the  calf 
of  the  leg,  are  of  greater  size  and  strength  than  in  monkeys,  be- 
sides acting  with  the  mechanical  advantage  arising  from  the  long 
lever  which  the  heel  affords  for  the  insertion  of  their  united  ten- 
dons ;  and  by  the  direction  of  the  foot,  which  forms  a  right  angle 
with  the  leg. 

895.  The  form  of  the  chest  exhibits  similar  differences.  In 
quadrupeds  the  thorax  is  compressed  laterally,  and  is  deepest 
from  the  spine  to  the  sternum  ;  a  structure  which  allows  the 
front  legs  to  come  nearer  together,  and  to  support  with  more 
effect  the  front  part  of  the  trunk.  But  in  man  the  thorax  is 
flattened  anteriorly  and  extends  more  in  width,  that  is,  from-  side 
to  side,  thus  throwing  out  the  shoulders,  and  giving  a  more  ex- 
tensive range  to  the  motions  of  the  arms. 

896.  That  the  erect  posture  is  natural  to  man  is  strongly  indi- 
cated by  the  position  of  the  head  with  respect  to  its  articulation 
with  the  spine,  which  takes  place  at  the  middle  of  its  basis  ;  and 
thus,  by  the  great  extension  of  the  occiput,  its  weight  is  more 
nearly  balanced  than  it  is  in  the  monkey.  The  cervical  vertebras 
of  the  monkey  have  very  long  and  prominent  spinous  processes, 
evidently  adapted  to  give  greater  purchase  to  the  muscles  sus- 
taining the  head  of  which  the  front  part  considerably  preponde- 
rates, in  consequence  of  the  elongation  of  the  jaws,  and  the  back- 
ward position  of  the  centre  of  motion. 

897.  The  same  design  may  be  traced  in  the  position  of  the 
eyes,  the  mouth,  and  the  face  in  general ;  and  is  so  obvious  as  to 


PECULIARITIES   OF    HUMAN    CONFORMATIOiV.  371 

have  ebeen  noticed  by  Ovid,  while  describing  the  formation  of 
man,  in  the  following  celebrated  lines : 

"Pronaque  cum  spectani  animalia  caetera  terram, 
Os  homini  sublime  dedit:  ccelumque  videre 
Jussit,  et  erectos  ad  sidera  tollere  vultus." 

898.  All  the  internal  organs  have  been  regulated  by  the  same 
intention.  The  human  heart  is  placed  obliquely  in  the  chest,  and 
rests  by  a  flat  surface  on  the  diaphragm,  to  which  its  investing 
membrane,  the  pericardium,  is  firmly  attached.  In  quadrupeds, 
no  such  attachment  exists ;  but  the  heart  is  situate  more  perpen- 
dicularly with  the  apex  directly  downwards,  and  cannot  be  felt, 
as  in  man,  striking  on  the  left  side  of  the  ribs  at  each  contraction 
of  the  ventricles. 

899.  The  fore  legs  of  quadrupeds  are  in  general  appropriated 
solely  to  the  support  and  progressive  motion  of  the  body.  In 
some  instances,  indeed,  they  are  employed,  besides,  in  other  actionsj 
such  as  seizing  and  securing  their  prey,  raking  and  digging  up 
the  earth,  or  climbing  and  laying  hold  of  the  branches  of  trees  ; 
but  it  is  only  in  a  few  species,  and  chiefly  amongst  the  monkey 
tribes,  which  resemble  man  in  their  form,  that  they  are  instrumental 
in  carrying  food  to  the  mouth,  or  even  in  grasping  weapons  of 
oftence.  But  in  man  the  superior  extremity  being  entirely 
released  from  the  ofiice  of  maintaining  any  portion  of  the  weight 
of  the  trunk,  is  at  liberty  to  be  employed  for  a  great  variety  of 
purposes;  and  the  exquisite  structure  of  the  human  hand,  which 
has  already  been  noticed,  renders  this  exemption  of  still  greater 
value,  and  constitutes  unquestionably  one  of  the  great  perfections 
which  mark  the  human  structure,  as  compared  with  that  of  the 
brute  creation.  The  arm  and  head  are  thus  rendered  an  organ 
at  once  of  prehension  and  of  touch,  for  both  of  which  purposes 
it  is  admirably  adapted  by  the  great  latitude  and  variety  of  move- 
ments it  is  capable  of  executing.  One  of  the  chief  sources  of 
perfection  in  the  hands  is  the  structure  of  the  thumb,  which  is 
furnished  with  muscles  of  so  great  a  power,  compared  with  those 
of  the  fingers,  as  to  enable  it  to  oppose  and  balance  their  united 
strength.  Hence  it  is  enabled  to  grasp  a  spherical  body,  and  to 
retain  firm  hold  of  many  objects,  which  otherwise  could  not  have 
been  held  without  the  united  efforts  of  both  hands.  This  con- 
formation is  pecuhar  to  man  ;  for  the  paw  of  a  monkey  cannot 
exercise  the  same  force  and  readiness  of  prehension,  in  conse- 
quence of  the  thumb  being  inferior  in  strength  to  the  other  fingers. 

900.  The  great  perfection  of  the  organs  which  modulate  the 
voice  and  produce  so  great  a  variety  of  articulate  sounds,  is 
another  striking  instance  of  the  high  destination  to  which  the 
human  structure  has  been  adapted.  In  those  tribes  of  monkeys 
which  come  nearest  to  the  human  conformation,  the  power  of 


372  COMPARATIVE    PHYSIOLOGY. 

Uttering  articulate  sounds  is  prevented  by  the  interposition  of  two 
sacks  connected  with  the  larynx,  which  receive  part  of  the  air 
when  the  animal  uses  any  effort  to  expel  it  from  the  lungs. 

901.  The  structure  of  the  digestive  organs  in  the  human 
species  is  similar  to  that  of  many  quadrupeds,  and  has  generally 
been  regarded  as  intermediate  between  that  of  the  carnivorous 
tribes,  and  of  those  that  live  altogether  on  vegetable  food.  Man 
may  very  justly,  and  almost  exclusively  be  entitled  to  the  appel- 
lation of  an  omnivorous  animal ;  being  equally  capable  of  sub- 
sisting on  difierent  kinds  of  aliment;  and  also  of  using  at  the 
same  time  a  great  mixture  of  different  sorts  of  food.  No  other 
animal  is  capable  of  so  great  a  versatility  of  powers  in  this  re- 
spect. It  has  also  been  remarked,  amongst  the  characteristic 
circumstances  of  the  human  race,  that  whilst  other  animals  are 
contented  with  food  in  the  state  in  which  nature  offers  it,  man 
alone  employs  artificial  processes  for  improving  its  flavour,  and 
rendering  it  more  fit  for  digestion.  Man  is  the  only  animal  that 
is  known  to  practise  the  art  of  cookery ;  an  art  which  indeed 
appears  necessary  to  enable  the  stomach  to  extract  from  his 
usual  food  all  the  nutriment  it  is  capable  of  yielding. 

902.  The  teeth  of  man  are  distinguished  from  those  of  all  the 
other  mammalia  by  their  being  arranged  in  either  jaw,  in  a  uniform 
unbroken  series ;  and  also  by  the  circumstance  of  their  being  all 
of  the  same  length.  The  cuspidati,  or  eye-teeth,  as  they  are 
called,  which  correspond  to  the  canine  teeth  in  quadrupeds,  are, 
perhaps,  at  first  a  little  longer  than  the  others,  but  their  sharp 
points  are  soon  worn  down  to  a  level  with  the  rest.  In  all  the 
monkey  tribes,  these  teeth  are  long  and  prominent,  and  are 
separated  by  an  interval  from  the  neighbouring  teeth.  The 
cutting  teeth  in  the  lower  jaws  slant  backwards  in  the  monkey, 
and  the  jaw  itself  has  the  same  diredtion  ;  but  in  man  these  teeth 
are  perpendicular,  and  in  a  line  with  the  front  of  the  jaw,  which 
descends  to  form  the  prominence  of  the  chin,  a  part  of  the  face 
which  does  not  exist  even  in  the  orang  utan.  The  tubercles  on 
the  surface  of  the  grinders  are  different  in  their  shape,  both  from 
the  ridges  of  enamel  on  the  crowns  of  the  teeth  of  herbivorous 
anitnals,  and  from  the  sharp-pointed  eminences  on  the  grinders  of 
carnivorous  animals. 

903.  Thehumanbrainis  not  only  larger  in  its  relative  proportion 
to  the  body  than  in  any  other  of  the  mammalia,  but  its  absolute 
size  is  greater,  if  we  except  only  that  of  the  elephant,  and  of  the 
whale.  With  these  few  exceptions,  all  the  larger  animals  with 
which  we  are  more  commonly  acquainted,  have  brains  absolutely, 
and  even  considerably  smaller  than  that  of  man.  Besides  the 
prodigious  expansion  of  the  hemispheres,  we  may  remark  in  the 
human  brain  a  more  elaborate  structure,  and  a  more  complete 
development  of  all  its  minuter  parts.     There  is  no  part  of  the 


PECULIARITIES  OF    HUMAN   CONFORMATION.  373 

brain  found  in  any  animal,  which  does  not  exist  also  in  man  ; 
whilst  several  of  those  which  are  found  in  man  are  cither  ex- 
tremely small,  or  altogether  absent  in  the  brains  of  the  lower 
animals.  Sommerring  has  enumerated  no  less  than  fifteen  visible 
and  material  anatomical  differences  between  the  human  brain 
and  that  of  the  ape.  The  proportion  of  medullary  to  cortical 
substance  is  greater  in  the  human  brain  than  in  that  of  other 
animals. 

904.  Although  the  negro  race  is  a  branch  of  the  great  family 
of  man,  and  although  the  peculiarities  which  distinguish  the  con- 
formation of  that  race  rank  only  as  varieties  in  the  species,  it  yet 
cannot  be  denied,  that  in  almost  every  one  of  the  circumstances 
in  which  it  differs  from  the  type  of  the  Caucasian  race,  it  exhibits 
an  approach  to  the  structure  of  the  monkey  or  quadrumanous 
tribe  of  animals.  In  nothing  is  this  approximation  more  remark- 
able, than  in  the  proportion  between  the  size  of  the  face  as  com- 
pared with  that  of  the  brain.  One  of  the  most  convenient 
methods  of  roughly  estimating  this  proportion  is  that  invented  by 
Professor  Camper.  Drawing  a  line  from  the  most  prominent 
part  of  the  frontal  bone,  to  the  anterior  point  of  the  upper  jaw 
bone,  just  at  the  roots  of  the  incisor  teeth,  which  is  called  the 
facial  line,  it  is  to  be  intersected  by  another  hne,  drawn  from  the 
external  orifice  of  the  ear  to  the  inferior  edge  of  the  aperture  of 
the  nostrils.  The  angle  formed  by  these  tw^o  lines  is  the  facial 
angle  of  Camper,  which  determines  by  its  magnitude  the  degree 
of  preponderance  of  the  bones  of  the  cranium,  in  which  the  brain 
is  contained,  over  those  of  the  face,  which  contain  the  organs  of 
sense. 

905.  In  man  the  facial  angle  is  greater  than  in  other  animals  ; 
it  differs,  however,  in  different  varieties  of  the  human  race,  and 
appears  to  indicate  with  tolerable  exactness  the  comparative 
degree  of  intellectual  excellence  appertaining  to  each  variety. 
In  the  Caucasian  variety  the  facial  angle  is  between  80°  and  90°; 
in  the  MongoUan,  75°;  in  the  American  Indian,  73^°;  in  the 
Negro  it  is  only  70°.  Pursuing  the  application  of  this  test  to  the 
lower  mammalia,  we  find  it  in  the  orang  utan  reduced  to  65° ; 
in  the  baboon,  45° ;  in  the  mandrill,  one  of  the  most  ferocious  of 
that  tribe,  only  30°.  The  mastiff  has  a  facial  angle  of  41°,  the 
bull-doo;  of  35°.  In  the  feline  tribe  it  is  still  farther  diminished ; 
being  only  28°  in  the  leopard.  In  the  sheep  and  hare  it  is  30,  in 
the  horse  it  is  only  23°. 

906.  The  varieties  in  the  magnitude  of  the  facial  angle  have 
thus  been  traced  through  a  number  of  gradations  amongst  differ- 
ent tribes  of  mammalia  and  also  of  birds,  till  we  arrive  at  its 
almost  total  obhteration  in  the  snipe  and  the  wood-cock,  animals 
which  are  reputed  to  be  extremely  deficient  in  intelligence. 

907.  The  projection  of  the  bones  of  the  face,  which  tends  to 

32 


374  COMPARATIVE    PHYSIOLOGY. 

diminish  the  facial  angle,  is  universally  considered  as  expressive 
of  stupidity  or  ferocity.  An  ample  and  projecting  forehead,  on 
the  contrary,  is  associated  in  our  minds  with  the  idea  of  superior 
intelhgence.  It  was  probably  for  that  reason  that  the  owl  was 
selected  by  the  Athenians  as  the  emblem  of  wisdom.  In  the  sta- 
tutes of  their  divinities,  the  Greek  sculptors  have  exaggerated  the 
facial  angle,  making  it  as  much  as  100°,  which  is  considerably 
greater  than  it  is  ever  found  in  the  human  form.  The  Itahan 
painters,  also,  in  their  representation  of  saints,  have  often  given 
them  a  facial  angle  of  95°. 

908.  But  in  applying  this  method  to  some  of  the  most  saga- 
cious species  of  animals,  such  as  the  horse,  which,  as  we  have 
seen,  has  a  very  small  facial  angle,  we  meet  with  great  and 
striking  exceptions.  We  arrive  at  more  correct  determination 
of  the  proportional  development  of  the  face  and  brain,  by  com- 
paring, as  proposed  by  Cuvier,  the  areas  respectively  occupied 
by  each  in  a  longitudinal  vertical  section  of  the  head.  But  in  the 
elephant  all  these  criteria,  but  especially  the  admeasurement  by 
the  facial  angle,  fail,  in  consequence  of  the  great  projection  of 
the  frontal  bones,  which  are  raised  to  a  considerable  distance 
from  the  brain  by  the  interposition  of  large  cells,  or  frontal 
sinuses,  and  which  give  an  undue  proportion  to  the  size  of  the 
forehead.* 

909.  Daubenton  proposed,  for  the  comparison  of  different  skulls 
with  one  another,  what  he   called  his  occipital  lines;  the  one 

'passing  from  the  posterior  margin  of  the  great  occipital  foramen 
through  the  lower  edge  of  the  orbit;  the  other,  taking  the  direction 
of  the  opening  itself,  beginning  at  its  posterior  edge,  and  touching 
the  articular  surface  of  the  condyles.  The  angle  formed  by  the 
intersection  of  these  Unes  is  his  occipital  angle.  But  the  variations 
of  this  angle  are  too  inconsiderable  to  furnish  sufficient  criteria  of 
the  character  of  the  head.f 

2.  Peculiarities  in  the  Conformation  of  other  Mammalia.'^ 

910.  The  bones  of  quadrupeds  appear,  as  Blumenbach  observes, 
to  possess  a  less  fine  and  delicate  texture  than  those  of  man. 

'*'  [A  striking  proof,  that  the  facial  angle  cannot  be  regarded  as  a  measure  of 
the  intellect  is  the  fact,  that  in  children  it  reaches  as  high  as  90° ;  several 
degrees  higher  than  in  the  adult.] 

f  [Blumenbach's  method,  by  what  he  called  the  norma  verticalis,  consisted 
in  selecting  two  bones,  the  frontal  from  those  of  the  cranium,  and  the  superior 
maxillary  from  those  of  the  face,  and  comparing  them  with  each  other,  by  re- 
garding them  vertically,  placing  the  great  convexity  of  the  cranium  di- 
rectly before  him,  and  marking  the  relative  projections  of  the  maxillary  bone 
beyond  the  arch  of  the  forehead.  But  this  method  does  not  indicate  the  depth 
of  the  maxillary  bone,  or  of  the  os  frontis,  or  their  comparative  areas.  The 
view  thus  obtained  is,  therefore,  partial.] 


MAMMALIA.  375 

Their  fibres  are  more  easily  loosened  by  maceration,  and  are  of  a 
coarser  grain ;  this  is  more  particularly  observable  in  the  jaw- 
bones and  the  ribs. 

911.  The  spine  is  formed  of  the  same  classes  of  vertebra3  as  in 
man,  namely  the  cervical,  dorsal,  lumbar,  and  sacral.  In  all 
quadrupeds  "belonging  to  the  class  of  mammalia,  the  number  of 
cervical  vertebras  is  constantly  seven,  as  in  man.  The  length  or 
shortness  of  the  neck  has  no  influence  on  their  number,  though  it 
has  a  material  one,  of  course,  on  the  comparative  length  of  each 
individual  vertebras.  The  camelopard,  whose  neck  is  extended 
to  so  great  a  length;  and  the  mole,  in  which  it  is  so  short,  have 
each  of  them  seven  cervical  vertebras.  An  apparent  exception  to 
this  general  rule  occurs  in  the  three-toed  sloth,  in  which  Cuvier 
found  nine  vertebrae  of  the  neck  instead  of  seven ;  but  it  has  since 
been  found  that  the  two  last  of  the  cervical  vertebrae,  which 
appeared  to  be  supernumerary,  ought  properly  to  be  classed 
amongst  the  dorsal  vertebrse,  of  which  they  possess  the  distinctive 
characters.* 

912.  The  number  of  dorsal  vertebrae  depends  principally  upon 
that  of  the  ribs,  which  differ  in  different  quadrupeds,  and  are 
usually  more  numerous  than  in  man.  Their  transverse  and  spinous 
processes  are  generally  longer  than  in  man,  for  the  purpose  of 
affording  a  broader  surface  of  attachment  to  the  powerful  muscles 
which  support  the  head  and  neck. 

The  number  of  the  lumbar  vertebrae  is  various  in  different 
quadrupeds.  There  are  only  three  in  the  elephant;  five  in  the 
ass ;  six  in  the  horse  ;  and  seven  in  the  camel.  Still  greater 
differences  are  met  with  in  the  number  of  component  parts  of  the 
sacrum. 

913.  Most  quadrupeds  have  a  prolongation  of  that  part  of  the 
skeleton  which  corresponds  to  the  os  coccygis  of  man,  and  which 
in  them  composes  the  tail,  and  consists  of  a  great  number  of 
imperfectly  formed  vertebrae. 

914.  The  thorax  of  quadrupeds  is,  as  we  have  already  noticed, 
more  compressed  laterally,  but  deeper  from  the  spine  to  the 
sternum,  than  it  is  in  the  human  skeleton.  The  scapula  is  constantly 
found ;  but  in  most  tribes  there  is  no  clavicle  whatever,  and  in 
others  only  a  short  rudiment  of  that  bone,  connected  merely  with 
the  muscles.  In  other  respects,  the  number  and  connexions  of 
the  bones  of  the  extremities  are  generally  very  similar  to  the 
human  conformation;  we  may  observe,  however,  that  the  os 
femoris  is  usually  much  shorter  than  the  tibia,  and  being  covered 
by  the  large  muscles  which  attach  it  to  the  trunk,  appears  to 
belong  to  that  division  of  the  body.     The  bones  of  the  carpus  and 

*  See  a  paper  by  Mr.  Thomas  Bell,  Philosophical  Magazine,  third  series, 
iii.  376. 


376  COMPARATIVE    PHYSIOLOGY. 

tarsus,  together  with  those  of  the  fingers,  are  in  many  cases 
exceedingly  conripressed,  and  some  of  them  are  so  consohdated 
together,  as  not  to  be  distinguishable  as  separate  bones. 

915.  In  all  the  mammalia  we  find  a  peculiar  bone,  called  the 
intermaxillary  hone,  interposed  between  the  two  upper  jaw- 
bones, and  locked  in  between  them ;  its  office  appears  ..to  be  to 
contain  the  upper  incisor  teeth,  when  these  teeth  exist ;  but  it  is 
also  met  with  when  there  are  no  incisor  teeth. 

916.  The  number,  form,  and  internal  structure  of  the  teeth  is 
exceedingly  diversified  in  the  different  tribes ;  and  afford  excel- 
lent characters  for  the  distinction  of  orders  and  genera  of  the 
class  mammalia.  As  these  characters  have  a  strict  relation  to 
zoological  classification,  we  shall  abstain  from  entering  here  into 
the  details  of  this  subject. 

917.  In  proceeding  to  notice  the  peculiarities  of  structure  in 
the  mammalia,  we  shall  next  examine  the  organs  of  the  func- 
tions of  assimilation,  to  which  that  part  of  the  skeleton  we  have 
just  adverted  to,  namely,  the  jaws  and  teeth,  are  subservient. 

918.  The  tongue  of  quadrupeds  is,  for  the  most  part,  more 
narrow,  long,  and  slender  than  that  of  man.  Except  in  the 
genus  simia,  we  do  not  meet  with  any  structure  corresponding 
to  the  uvula.  The  oesophagus  has  two  layers  of  muscular  fibres, 
which  have  a  spiral  course,  and  cross  one  another.  This  struc- 
ture gives  it  greater  power  of  propelling  its  contents  into  the 
stomach ;  a  power  which  is  the  more  required,  inasmuch  as  the 
food  has  often  to  ascend  considerably  in  passing  along  this 
canal. 

919.  The  conformation  of  the  stomach  presents  very  consi- 
derable diversities,  apparently  determined  by  the  habit  of  the 
animal  and  the  nature  of  its  food.  From  the  simple  structure  it 
exhibits  in  the  purely  carnivorous  tribes,  we  may  observe  a  gra- 
dually increasing  compHcation  as  we  pass  to  those  that  feed  on 
fish,  and  on  vegetable  aliment.  In  the  latter  orders  of  mammalia, 
and  especially  in  the  ruminants,  we  meet  with  a  very  complicated 
apparatus  for  digestion.  But  these  diversities  will  come  more 
properly  to  be  noticed  in  the  examination  of  the  orders  and  fami- 
lies to  which  they  relate.  It  will  be  sufficient  here  to  remark,  that 
the  stomach  is  often  divided  into  several  distinct  portions,  such 
as  the  cardiac  and  pyloric ;  and  often  presents  several  inter- 
mediate subdivisions,  and  expansions  into  separate  pouches,  so 
as  to  exhibit  the  appearance  of  a  multiplicity  of  cavities  or 
stomachs.  They  differ  also  considerably  as  to  the  degree  in 
which  the  glandular  structures  attached  to  their  coats  are  deve- 
loped in  different  parts. 

920.  Similar  varieties  are  met  with  in  the  structure  of  the 
intestines  of  different  mammalia.  As  a  general  rule,  to  which, 
however,  there  are  several  exceptions,  it  may  be  remarked,  that 


MAMMALIA.  377 

the  intestinal  canal  is  much  shorter,  and  more  contracted  in  its 
diameter,  in  carnivorous  animals  than  in  those  which  feed  on 
vegetables.  This  probably  depends  on  the  more  rapid  assimila- 
tion of  animal  than  of  vegetable  materials;  the  latter  requiring  a 
more  complicated  apparatus,  more  capacious  cavities,  and  a 
more  extensive  surface  both  for  secretion  and  absorption.  It  has 
been  observed  that  the  canal  of  the  intestines  is  longer  in  the 
domesticated  breed  than  in  the  wild  animal  of  the  same  species. 
Thus,  in  the  wild  boar,  the  length  of  the  intestines  is  to  that  of 
the  body  in  the  proportion  of  nine  to  one ;  but  in  the  tame  animal 
the  proportion  is  as  thirteen  to  one.  In  the  domestic  cat  it  is  as 
five  to  one ;  in  the  wild  cat  as  three  to  one.  It  may  also  be 
remarked  that  in  the  class  mammalia,  the  comparative  length  of 
the  intestinal  canal  is  greater  than  in  any  of  the  other  vertebrated 
classes ;  and  diminishes  successively  as  we  compare  it  in  birds, 
reptiles,  and  fishes. 

921.  The  liver  in  the  mammalia  generally,  is  divided  into  a 
greater  number  of  lobes,  and  the  divisions  penetrate  deeper  into 
its  substance,  than  in  man.  In  a  great  many  instances,  as  in  the 
horse  and  the  goat,  there  is  no  gall-bladder,  the  bile  being  car- 
ried at  once  by  the  hepatic  ducts  into  the  intestine.  Occasionally 
when  the  gall-bladder  is  present,  there  exist  also  hepato-cystic 
ducts  which  convey  the  bile  directly  from  the  liver  into  the  gall- 
bladder, and  not  by  a  retrograde  course,  as  in  man. 

The  mammaha  is  the  only  class  of  animals  provided  with 
omentum,  which,  in  some,  as  in  the  racoon,  is  particularly  large 
and  stored  with  fat. 

The  kidney  generally  presents  a  lobulated  appearance  ;  some- 
times to  such  a  remarkable  degree,  as  to  bear  a  resemblance  to 
a  bunch  of  grapes,  being  composed  of  numerous  small  and  dis- 
tinct portions,  connected  together  by  their  blood-vessels  and  ex- 
cretory ducts.  The  urinary  bladder  is  more  capacious  in  herbi- 
vorous than  in  carnivorous  quadrupeds. 

The  heart  of  the  mammalia  corresponds  in  every  essential 
particular  of  its  structure  with  the  human  conformation ;  but  it 
differs  in  its  position  with  regard  to  the  other  organs,  being 
situate  more  longitudinally,  and  resting  on  the  sternum,  which  is 
below  it,  and  not  on  the  diaphragm,  as  in  man.  Hence,  also, 
the  direction  of  its  axis  is  not  so  oblique,  and  it  is  placed  more  in 
the  centre  of  the  chest ;  and  the  pericardium  is  scarcely  at  all 
connected  with  the  diaphragm. 

922.  In  many  quadrupeds  the  thoracic  duct  is  double,  and 
forms  more  distinctly  than  in  man  the  enlai'gement  which  has 
been  termed  the  receptaculum  chyli.  The  mesenteric  glands  are 
frequently  collected  into  a  considerable  mass,  called  the  pancreas 
of  Jlsellius. 

32* 


378  COMPARATIVE    PHYSIOLOGY. 

923.  From  the  consideration  of  the  organs  of  nutrition  we 
pass  on  to  those  of  the  sensorial  functions,  and  shall  for  this  pur- 
pose revert  to  the  osteology,  in  as  far  as  relates  to  the  bones 
which  protect  the  brain  and  principal  organs  of  the  senses. 

924.  The  divisions  of  the  cranium  of  quadrupeds  into  separate 
bones,  differs  but  little  from  that  of  the  human  skull.  The  os 
frontis  is  frequently  found  divided  into  two  lateral  portions  by 
the  prolongation  of  the  sagittal  suture  forwards  to  the  root  of  the 
nose.  Sometimes,  again,  the  sagittal  suture  is  obliterated  by  the 
consolidation  of  the  two  parietals  into  a  single  bone ;  in  other 
cases,  these  bones  are  united  with  the  occipital.  We  often  find, 
also,  a  bone,  distinct  from  the  temporal,  termed  the  tympanic 
bone,  provided  for  containing  the  tympanum  of  the  ear.  But  it 
may  be  observed,  in  general,  that  the  sutures  present  fewer  in- 
dentations, and  less  irregularity  in  their  course  in  the  skulls  of 
quadrupeds  than  in  man,  a  circumstance  which  is  naturally 
explicable  by  the  smaller  development  of  the  brain,  and  conse- 
quent diminution  of  the  general  size  of  the  cranium.  From  the 
position  of  the  head  in  the  quadruped  the  occipital  foramen  is 
situate  less  anteriorly  in  the  basis  of  the  skull  than  in  man,  and 
is  for  the  most  part  nearly  vertical  in  its  position.  The  tentorium 
sometimes  contains  within  the  laminae  of  the  dura  mater,  which 
compose  it,  several  strong  plates  of  bone,  and  the  same  thing  has 
also  been  observed  in  the  falx. 

925.  The  brain  of  quadrupeds  is  considerably  smaller,  when 
compared  with  the  size  either  of  the  spinal  cord  or  the  cranial 
nerves,  than  in  man.  The  cerebral  hemispheres  are  also  much 
smaller  compared  with  the  cerebellum.  This  arises  in  a  great 
measure  from  the  absence  of  the  posterior  lobes  of  the  brain, 
which  in  man,  when  viewed  from  above,  conceals  the  cerebellum: 
whereas  in  quadrupeds  the  cerebellum  is  brought  immediate!}' 
into  view  in  removing  the  upper  bones  of  the  skull.  In  the  proper 
quadrupeds  the  anterior  lobes  of  the  brain  extend  forwards  into 
two  large  processes,  called  the  processus  mamillares,  which  give 
origin  to  the  olfactory  nerves,  and  which  contains  a  cavity  on 
each  side,  communicating  with  the  lateral  ventricle,  being  in  fact 
its  anterior  prolongation.  On  the  other  hand,  this  ventricle  has 
no  posterior  prolongation,  there  being  no  posterior  lobe. 

926.  Every  part  of  the  organ  of  smell  is  developed  in  quadru- 
peds in  a  degree  corresponding  to  the  greater  extent  and  acute- 
ness  in  which  they  enjoy  this  sense,  compared  with  man.  The 
ethmoid  bone  is  much  more  complicated  in  its  structure,  as  well 
as  larger  in  its  dimensions ;  the  turbinated  bones  are  considerably 
larger,  more  intricate  in  their  formation,  and  present  a  much 
more  extensive  surface,  being  composed  either  of  a  great  multi- 
tude of  arborescent  laminse,  or  of  numerous  spiral  convolutions. 


MAMMALIA.  379 

The  internal  nasal  cavities  are  also  generally  enlarged,  and  par- 
ticularly the  frontal  sinuses.  ^ 

927.  The  organ  of  hearing  also  frequently  presents  a  greater 
complication  of  structure  than  in  man.  A  cavity,  called  by 
Sommerring,  the  bulla  ossea,  communicates  with  that  of  the  tym- 
panum, and  corresponds  with  the  mastoid  cells  in  the  human 
subject.  In  the  aquatic  mammalia  the  external  meatus  is  fur- 
nished with  a  valve  for  the  purpose  of  excluding  water  from  the 
passage.  In  these  animals,  also,  as  well  as  in  those  that  live 
under  ground,  the  external  ear  is  altogether  wanting.  The  struc- 
ture of  the  internal  parts  of  the  organ  agree  in  all  essential  points 
with  those  of  the  human  ear.  The  cochlea  sometimes  makes  an 
additional  turn  in  its  spiral  convolution. 

928.  The  eyes  of  mammalia  exhibit  considerable  variety  as 
to  the  position  of  their  axes  with  respect  to  the  general  direction 
of  the  head.  They  are  generally  separated  to  a  greater  distance, 
and  directed  laterally.  The  figure  of  the  globe  is  nearly  spherical, 
as  in  man ;  but  in  several  quadrupeds  the  sclerotic  coat  is  much 
thicker  and  firmer  at  its  posterior  than  at  its  anterior  part.  The 
choroid  coat  is  distinctly  divisible  into  two  layers,  of  which  the 
internal  bears  the  name  of  the  tunica  Ruyschiana,  and  which 
often  exhibits  at  the  back  of  the  eye  the  most  brilliant  colours. 
This  coloured  portion  of  the  choroid  is  known  by  the  name  of 
the  tapeium. 

929.  Several  quadrupeds  have  an  additional  lacrymal  gland, 
besides  that  which  corresponds  to  the  one  in  man ;  and  also 
another  gland,  situate  near  the  nose,  and  termed  the  glandula 
Harden.  The  globe  of  the  eye  in  quadrupeds  is  also  provided 
with  an  additional  muscle,  the  suspensoiius  oculi,  for  the  purpose 
of  supporting  its  weight.  Many  quadrupeds  also  possess  a  third, 
or  internal  eye-lid,  called  the  nictitating  membrane,  which  is  very 
large  and  moveable  in  the  cat,  and  all  the  animals  belonging  to 
the  same  genus. 

930.  The  panniculus  carnosus  is  a  muscular  expansion,  situate 
immediately  under  the  skin,  and  subservient  to  the  movements  of 
the  integuments,  which  it  suddenly  corrugates  and  throws  into 
wrinkles,  thereby  driving  off  insects  or  shaking  away  any  other 
offensive  matter,  is  pecuhar  to  quadrupeds,  not  being  found  in 
man ;  unless  the  platysma  myoides  of  the  neck  be  considered  as 
a  muscle  having  an  analogous  function  with  relation  to  the  skin 
of  the  neck. 

931.  In  many  quadrupeds  some  of  the  sebaceous  glands  of  the 
integuments  are  very  much  developed.  In  some  predacious  ani- 
mals, a  gland  exists  in  the  orbit,  described  by  Nuck,  and  of  which 
the  excretory  duct  opens  near  the  last  tooth  of  the  upper  jaw.  It 
appears  referable  to  the  class  of  salivary  glands.   Another  gland, 


380  COMPARATIVE    PHYSIOLOGY. 

particularly  noticed  by  Professor  Jacobson,  and  of  which  the  use 
is  wholly  unknown,  is  generally  met  with  in  the  anterior  and 
lower  part  of  the  cavity  of  the  nostrils:  this  he  has  called  the 
nasal  gland  of  Steno.  i 

3.   Quadrumana. 

932.  We  have  already  had  occasion,  when  describing  the 
distinctive  marks  by  which  the  human  structure  is  characterized, 
when  compared  with  that  of  the  monkey,  to  point  out  several 
circumstances  which  are  deserving  of  notice  in  the  anatomy  of 
this  tribe  of  mammalia.  Of  all  the  animals  of  the  family  of  the 
quadrumana,  the  orang-utan  {simia  satyrus,  Geoff.)  is  that  species 
which  makes  the  nearest  approach  to  the  human  conformation. 
This  approximation  is  observable  in  the  position  of  the  great 
occipital  foramen  of  the  skull,  which  is  placed  further  forwards 
than  in  other  kinds  of  apes ;  in  the  distinctness  and  serrated  form 
of  the  sutures  of  the  cranial  bones ;  in  the  absence  of  the  inter- 
maxillary bone ;  in  the  eyes  .  being  directed  forwards ;  in  the 
smallness  of  the  os  coccygis,  cornposed,  as  in  man,  of  five  im- 
perforated bones;  in  the  possession  both  of  a  coecum-  and  an 
appendix  vermiformis;  and  in  the  oblique  position  of  the  heart 
with  respect  to  the  cavity  of  the  thorax. 

933.  A.  still  more  remarkable  peculiarity  of  structure  in  the 
orang-utan  is  that  discovered  and  described  by  Camper ;  namely, 
two  membranous  sacs,  which  communicate  with  the  glottis,  and 
deprive  the  animal  of  the  power  of  giving  utterance  to  sounds. 

934.  In  other  species  of  this  order  we  trace  still  further  devia- 
tions from  the  human  structure.  The  laryngeal  sacs  are  found 
in  many  species  of  baboons ;  these  are  either  single  or  double, 
and  communicate  with  the  larynx  by  openings  between  the  os 
hyoides  and  the  thyroid  cartilage.  The  simia  seniculus,  and  the 
simia  beelzebub,  have  a  large  dilatation  of  the  middle  of  the  body 
of  the  OS  hyoides,  which  is  expanded  into  a  spherical  bony  cavity. 
This  cavity,  instead  of  interfering  with  the  sonorous  vibrations, 
adds  to  their  strength,  and  gives  the  power  of  producing  those 
loud  intonations  which  are  peculiar  to  this  tribe,  and  from  which 
they  have  obtained  the  name  oi  howling  apes. 

935.  The  mandrill  baboon  has  seven  instead  of  five  lumbar 
vertebrae.  The  appendix  vermiformis  of  the  coecum  is  not  met 
with  in  many  species  of  apes.  The  crest  of  the  occipital  bone, 
though  very  large  in  the  baboon  of  Borneo,  is  scarcely  percepti- 
ble in  most  monkeys.  The  central  foramen  of  the  retina  disco- 
vered in  the  human  eye  by  Sommerring,  has  been  seen  in  the 
eyes  of  many  animals  of  this  order. 

936.  In  the  lemur  tardigradus,  and  in  the  sloth,  a  singular 
structure  has  been  observed  by  Sir  Anthony  Carlisle,  with  regard 


MAMMALIA.  381 

to  the  distribution  of  the  arteries  of  the  limbs.  The  trunks  of  these 
arteries  suddenly  subdivide  as  they  enter  the  limb  into  a  great 
number  of  parallel  branches,  which  are  again  re-united  when  they 
arrive  at  the  remote  end  of  the  first  division  of  the  limb;  that  is, 
about  the  joints  corresponding  to  the  elbow  and  the  knee  in  man. 
After  tiieir  re-union  into  single  trunks,  these  arteries  proceed  to 
ramifv  in  the  usual  manner. 


4.  Chiroptera. 

937.  In  the  bat  tribe  we  have  to  notice  the  strictly  hinge-like 
nature  of  the  articulation  of  the  lower  jaw  with  the  skull,  which 
limits  its  motion  to  mere  opening  and  shutting,  and  excludes  all 
lateral  movements.  The  zygomatic  arches  are  expanded  and 
raised,  so  as  to  allow  room  for  the  large  and  powerful  muscles 
which  close  the  jaw.  The  parietal  bones  are  united  into  a  single 
bone.  The  sacrum  is  composed  of  four  bones  consolidated 
together.  Four  clavicles  are  met  with,  and  they  are  of  extra- 
ordinary length.  The  ulna  is  deficient  in  the  fore-arm,  or  exists 
only  in  a  rudimental  state,  as  a  slender  sharp-pointed  process  of 
the  radius.  The  phalanges  of  the  anterior  extremities  are  enor- 
mously lengthened  for  the  purpose  of  supporting  the  thin  mem- 
brane which  is  stretched  between  them,  and  which  serves  the 
office  of  wings.  The  tongue  of  the  bat  is  covered  with  sharp- 
pointed  horny  papillae. 

938.  The  vespertilio  noctula  is  remarkable  for  the  shortness 
of  the  intestinal  canal,  which  is  only  twice  the  length  of  the 
animal's  body.  In  the  vampire  bat,  on  the  contrary,  and  in  the 
vespertilio  caninus  it  is  seven  times  as  long.  In  all  bats,  not  only 
is  the  appendix  coeci  vermiformis  wanting,  but  also  the  coecum 
itself  The  epiglottis  is  also  wanting  in  most  of  the  animals  of 
this  tribe.  In  many  the  tongue  is  slender,  and  prolonged  into  an 
organ  of  suction.  The  pectoral  muscles  are  of  enormous  size; 
and  the  sternum  has  a  prominent  crest  for  the  purpose  of  affording 
an  extensive  surface  for  their  attachment.  The  eye  is  remarkably 
small ;  but  the  imperfections  which  probably  exist  in  the  sense 
of  sight  are  amply  compensated  by  the  singular  acuteness  of  that 
of  hearing,  the  organ  of  which  is  exceedingly  developed  ;  and 
also  by  the  extreme  sensibility  of  the  expanded  membranes  of  the 
vikings,  which  is  such  as  to  enable  the  bat  to  direct  its  fl[?ght 
through  the  most  intricate  passages  without  the  aid  of  the  sight, 
and  without  striking  against  the  obstacles  purposely  placed  in  its 
way. 

5.  Insectivora. 

939.  Among  the  animals  arranged  by  Cuvier  in  this  family, 
the  mole  presents  the  most  remarkable  peculiarities  of  conforma- 


382  COMPARATIVE   PHYSIOLOGY. 

tion,  both  as  regards  the  skeleton  and  the  internal  organs.  The 
sternum  has  the  same  crested  process  as  in  the  bat,  and  apparently 
with  the  same  design  of  enlarging  the  surface  of  attachment  to 
the  powerful  muscles  employed  in  digging.  But  the  anterior 
extremity  of  this  crest  is  still  farther  prolonged  into  a  sharp 
process,  having  the  figure  of  a  plough-share,  which  is  situate 
under  the  cervical  vertebras,  and  resembles  the  keel-like  projection 
we  shall  have  occasion  to  notice  in  the  sternum  in  birds.  The 
cervical  vertebrae  are  remarkable  for  having  no  spinous  processes. 
The  ligamentum  nuchse  is  particularly  strong,  and  is  almost 
wholly  ossified.  The  clavicle  is  of  a  singular  shape,  being  nearly 
cubical.  The  humerus  is  very  slender  in  the  middle,  and  re- 
markably expanded  at  both  its  extremities.  The  fore-paw  is 
provided  with  a  bone  of  a  pecuhar  shape,  called  the  falciform 
bone,  placed  at  the  end  of  the  radius.  The  phalanges  have  nu- 
merous processes,  and  are  furnished  with  sesamoid  bones ;  struc- 
tures which,  by  giving  considerable  mechanical  advantage  to  the 
muscles  that  move  them,  contribute  greatly  to  increase  their 
power.  The  great  muscles  of  the  trunk,  the  pectoraUs  major, 
the  latissimus  dorsi,  and  the  teres  major,  are  of  great  size,  and 
give  the  animal  great  facility  in  digging  the  ground,  and  throwing 
up  the  earth  as  it  proceeds. 

940.  The  ethmoid  bone  is  of  very  complicated  formation  in  the 
mole,  especially  in  the  numerous  convolutions  of  its  turbinated 
processes,  by  which  a  very  large  surface  is  given  to  the  Schnei- 
derian  membrane  which  lines  every  portion.  This  structure 
indicates  the  possession  of  a  very  acute  sense  of  smell.  The 
remarkable  development  of  the  internal  parts  of  the  ears,  is  also 
conclusive  evidence  of  the  delicacy  of  the  sense  of  hearing  in  this 
animal,  although  it  has  no  external  ear  whatever.  The  eye  is  so 
minute,  that  even  the  existence  of  that  organ  has  been  denied  by 
some  naturalists ;  it  is,  in  fact,  not  larger  than  the  head  of  a  pin. 
The  cavities  in  which  they  are  placed  are  so  very  superficial,  as 
scarcely  to  deserve  the  name  of  orbits.  The  zygoma  is  not 
arched,  but  straight,  and  as  slender  as  a  thread. 

6.  Plantigrada. 

941.  Animals  of  the  plantigrade  family  have  ~a  long  but  narrow 
intestinal  canal,  unprovided  with  any  coecum  or  appendix,  and 
consequently  not  presenting  any  marked  distinction  between  the 
small  and  the  large  intestines. 

942.  To  this  family  belongs  the  bear,  remarkable  for  possessing 
supernumerary  canine  teeth,  which  are  small,  and  situate  behind 
the  principal  ones.  The  stomach  is  divided  into  two  portions  by 
a  slight  contraction  in  the  middle ;  the  intestines  are  furnished 
with  remarkably  long  and  numerous  viUi ;  the  kidneys  are  con- 


MAMMALIA.  383 

glomerated ;   the  tentorium  is  bony;  the  nasal  cartilages  are 
extremely  mobile. 

943.  In  the  racoon,  another  animal  of  this  tribe,  the  valve  of 
the  colon  is  wanting,  and  the  omentum  is  very  large,  consisting 
of  innumerable  lines  of  fat,  disposed  in  a  reticular  form,  and 
connected  by  an  extremely  delicate  membrane  having  the  appear- 
ance of  a  spider's  web.  The  skin  of  the  neck  is  very  loosely 
connected  bv  cellular  substance  with  the  subjacent  muscles. 


7.  Digitigrada. 

944.  The  coecum  is  wanting  in  the  greater  number  of  the 
animals  of  this  tribe.  It  is  met  with,  however,  in  the  ichneumon. 
Many  have  anal  glands  and  follicles,  which  prepare  a  strongly 
odoriferous  secretion.  This  is  the  case  with  the  skunk,  pole-cat, 
and  several  others.  When  these  animals  are  pursued,  they  pour 
out  this  fetid  matter,  the  odour  of  which  is  so  offensive  as  to  deter 
their  pursuers  from  approaching  them.  The  civet  has  also  similar 
glands  that  secrete  the  peculiar  perfume  which  derives  its  name 
from  that  animal. 

945.  The  stomach,  in  the  weasel  tribe,  is  a  simple  cylindrical 
canal,  having  no  expanded  extremity  to  the  left  of  the  cardia ; 
but  the  oesophagus  enters  at  one  end,  and  the  intestine  proceeds 
from  the  other,  so  that  the  food  may  pass  quickly  through  it.  In 
the  stomach  of  the  sea  otter,  Sir  Edward  Home  describes  a 
remarkable  glandular  structure  near  the  pylorus.  The  receptacu- 
lum  chyli,  in  this  animal,  sends  two  trunks  to  form  the  thoracic 
duct,  which  have  frequent  communications,  so  that  there  are 
sometimes  three,  frequently  fom',  and  never  fewer  than  two 
branches  of  this  duct,  running  parallel  to  one  another.  In  two 
instances  the  foramen  ovale  of  the  heart  was  found  open,  but  the 
ductus  arteriosus  was  closed. 

946.  In  the  dog  a  row  of  mucous  glands,  corresponding  to  the 
labiales  and  buccales  in  man,  is  found  opposite  to  the  molar 
teeth,  having  several  small  openings  into  the  mouth.  A  large 
salivary  gland  also  exists  under  the  arch  of  the  zygoma,  covered 
by  the  masseter  muscle.  Its  duct  is  nearly  equal  in  size  to  that 
of  the  parotid,  and  opens  at  the  posterior  extremity  of  the  alveo- 
lar margin  of  the  upper  jaw.  What  is  called  the  icorm  in  the 
dog's  tongue,  is  merely  a  packet  of  tendinous  fibres,  passing 
longitudinally  the  whole  length  of  its  tongue,  and  lying  loose  in 
a  membranous  sheath,  unconnected  with  any  of  the  muscles.  It 
has  been  supposed  to  assist  in  lapping  up  fluids  in  the  peculiar 
way  in  which  dogs  are  observed  to  clrink.  There  is  a  popular, 
but  wholly  unfounded  idea,  that  the  extirpation  of  this  pretended 
worm,  is  a  preservation  against  hydrophobia.  The  anal  glands 
are  of  considerable  size. 


384  COMPARATIVE    PHYSIOLOGY. 

947.  The  thoracic  duct  is  double  in  the  dog,  and  forms  a  large 
receptaculum  chyli.  The  crista  occipitahs  varies  considerably 
in  its  degree  of  prominence  in  the  different  breeds  of  dogs.  In 
all,  the  tympanic  bone  is  distinct  from  the  temporal  bone,  being 
separated  from  it  by  a  suture.  The  urethra  passes  along  a  groove 
in  a  cylindrical  bone.  In  the  hysena,  however,  which  in  other 
respects  is  very  similar  to  the  dog,  this  bone  is  not  found.  The 
extremities  of  the  rings  of  the  trachea,  in  the  hyssna,  overlap  one 
another,  and  admit  of  being  much  compressed  ;  a  circumstance 

I  which  has    been  considered  as    connected  with  the  shrill  and 
piercing  cry  which  this  animal  is  capable  of  uttering. 

948.  The  genus  fehs,  of  which  the  lion  affords  the  most  re- 
markable example,  resembles  the  dog  in  many  circumstances  of 
conformation.  We  find  the  same  set  of  mucous  glands  about 
the  mouth,  and  at  the  extremity  of  the  rectum.  The  tongue  is 
beset  with  sharp  prickles,  the  points  of  which  are  directed  back- 
wards ;  they  are  of  such  strength  as  to  tear  off  the  skin  from  any 
part  which  the  lion  may  lick.  The  stomach  is  divided  by  a  slight 
middle  contraction,  into  a  cardiac  and  a  pyloric  portion.  The 
ductus  choledochus  forms  a  pouch  between  the  coats  of  the  in- 
testine for  receiving  the  pancreatic  duct.  In  all  animals  of  this 
genus  the  tentorium  is  bony.  The  zygoma  is  arched,  and  very 
large  and  prominent.  The  long  bristly  hairs  which  constitute 
the  whiskers,  receive  very  considerable  nervous  filaments,  and 
appear  subservient  to  the  sense  of  touch  in  a  very  remarkable 
degree.  Two  delicate  membranes  are  met  with  lying  under  the 
ligaments  of  the  glottis,  and  are  probably  the  cause  of  the 
piercing  sound  peculiar  to  animals  of  this  tribe.  The  retraction 
of  the  claws  into  a  sheath  is  matter  of  familiar  observation  in  the 
cat.  The  pupil  of  the  lion  is  circular,  but  that  of  the  cat  has  the 
form  of  a  vertical  sUt  when  closed ;  and  the  motions  of  the  iris 
appear  to  be  partly  voluntary. 

8.  Amphibia. 

949.  Whiskers  having  the  same  properties  are  likewise  found 
in  the  seal,  an  animal  of  aquatic  habits,  and  whose  conformation 
is  modified  with  reference  to  the  element  it  is  intended  to  inhabit. 
The  feet  act  as  fins,  adapted  for  swimming ;  the  radius  and  ulna 
are  flattened  ;  the  spine  is  very  flexible  ;  the  pelvis  very  narrow. 
The  bones  have  no  medullary  cavities.  Neither  the  parotid  nor 
the  sublingual  glands  are  met  with  in  this  or  any  other  animal  of 
the  order  of  amphibia,  belonging  to  the  class  mammaha ;  and 
the  teeth  are  adapted  chiefly  to  the  seizing  and  detention  of 
objects,  and  are  scarcely  capable  of  serving  the  purpose  of  masti- 
cation. The  stomach  is  a  straight  cyhnder,  having  no  cardiac 
expansion.     The  intestinal  canal  is  of  great  length,  thus  forming 


MAMMALIA.  385 

an  exception  to  the  general  rule  of  its  being  comparatively  short 
in  carnivorous  animals.  The  renal  veins  form  a  kind  of  net- 
work, the  reticulations  of  which  intersect  the  furrows  between 
the  mammary  processes  on  the  outer  surface  of  the  kidneys. 
The  proportional  size  of  the  brain  of  the  seal  is  greater  than  in 
most  mammaha. 

950.  The  eye  of  the  Greenland  seal  is  peculiarly  formed, 
having,  according  to  Blumenbach,  the  anterior  segment  of  the 
sclerotica,  or  that  immediately  behind  its  junction  with  the  cornea, 
thick  and  firm ;  its  middle  circle  thin  and  flexible ;  and  its  pos- 
terior part  very  thick  and  almost  cartilaginous,  while  the  cornea 
itself  is  thin  and  yielding.  The  whole  eye-ball  is  surrounded  by 
very  strong  muscles  capable  of  shortening  the  axis  of  the  eye, 
and  of  adapting  it,  according  to  circumstances,  to  distinct  vision 
in  air ;  while  in  their  ordinary  state  of  relaxation,  the  axis  of  the 
eye  being  lengthened,  the  animal  when  under  water  is  still 
enabled  to  see  objects  distinctly. 

951.  The  walrus,  another  animal  of  this  order,  is  remarkable 
for  the  form  of  its  teeth  and  tusks,  part  being  external ;  but  these 
fall  more  within  the  province  of  the  naturalist.  The  zootomist 
may  notice  in  this  animal  the  smallness  of  the  intermaxillary 
bone,  and  the  total  absence  of  the  gall  bladder. 

9.  Marsupialia. 

952.  The  marsupial  family  of  mammalia  compose  an  interest- 
ing group  of  animals,  which  present  many  remarkable  singularities 
in  their  internal  conformation  and  economy.  The  principal  of 
these  is  the  apparently  premature  birth  of  their  young,  which 
come  into  the  world  at  a  period  of  their  development  correspond- 
ing to  that  to  which  the  foetuses  of  mammalia  have  arrived  only 
a  few  days  after  conception.  Nearly  the  whole  extent  of  the 
integument  of  th^  fore  part  of  the  abdomen  forms  a  kind  of  sac 
or  pouch  for  the  reception  of  the  foetuses  in  their  early  state,  and 
whilst  they  present  only  a  shapeless  mass,  destitute  of  external 
members,  and  totally  incapable  of  locomotion.  They  become 
attached  to  the  nipples  of  the  mammary  glands,  situate  under  the 
integument  of  the  pouch  next  to  the  abdomen  of  the  mother ;  and 
they  remain  in  this  situation  for  a  long  time,  imbibing  nourish- 
ment from  these  glands,  until  they  acquire  a  growth  equal  to  that 
which  the  young  of  other  animals  attain  in  the  uterus  before 
birth.  Two  bones,  peculiar  to  these  animals,  and  therefore  called 
the  marsupial  bones,  are  expressly  provided  for  the  protection  of 
the  abdominal  viscera,  lying  in  the  horizontal  position  of  the 
trunk  above  this  extraordinary  pouch,  which  performs  the  func- 
tion of  a  supplementary  uterus.  It  is  farther  remarkable,  that 
the  same  bones  occur  in  the  skeleton  of  the  males,  where,  of 

33 


886  COMPARATIVE    PHYSIOLOGY. 

course,  there  are  no  pouches ;  and  also  in  those  species  where 
the  fold  forming  the  pouch  is  scarcely  perceptible.  The  uterus 
communicates  with  the  vagina,  not  by  a  single  opening,  but  by 
two  curved  lateral  tubes.  This  has  been  called  the  uterus  anfrac- 
tuosus,  to  distinguish  it  from  the  ordinary  form,  which  is  the 
uterus  simplex ;  the  uterus  hicornis,  which  has  two  horns,  either 
straight  or  convoluted  ;  and  the  double  uterus,  or  uterus  duplex, 
which  has  the  appearance  of  two  horns  opening  laterally  into 
the  vagina,  as  in  the  mole,  the  hai'e,  and  the  rabbit.  The  Fallo- 
pian tubes,  in  marsupial  animals,  are  much  enlarged  at  their 
extremities. 

953.  In  the  opossum,  the  cardiac  and  the  pyloric  openings  of 
the  stomach  are  placed  very  near  one  another.  The  anal  glands 
are  large.     The  tongue  is  covered  with  pointed  processes. 

954.  The  kangaroo  has  a  stomach  composed  of  three  pouches, 
but  in  consequence  of  the  power  which  different  portions  of  it 
possess  of  contracting  separately,  it  is  occasionally  divided  into 
a  much  greater  number  of  portions. 

955.  The  phascolome,  a  species  of  rat  from  Australia,  which 
possesses  an  abdominal  pouch,  is  remarkable  for  possessing,  in 
common  only  with  man,  and  the  orang-utan,  both  a  ccecum  and 
an  appendix  vermiformis. 

10,  Rodentia. 

956.  In  this  order  of  mammalia,  we  find  the  incisor  teeth  fur- 
nished with  enamel  only  in  front;  the  frontal  sinuses  are  absent; 
the  OS  frontis  is  divided  into  two  bones  by  a  middle  longitudinal 
suture,  and  the  tympanic  bone  is  distinct  from  the  temporal. 
The  brain  presents  no  appearance  of  convolutions  on  its  surface, 
the  eyes  are  placed  on  the  side  of  the  head,  so  that  the  direction 
of  their  axes  is  completely  lateral ;  and  the  orbits  are  not  sepa- 
rated from  the  temporal  fossse ;  the  coecum,  in  particular,  is  ex- 
ceedingly voluminous,  so«s  often  to  exceed  the  stomach  in  size. 
The  dormouse,  indeed,  presents  an  exception  to  this  rule,  being 
■destitute  of  any  coecum. 

957.  The  beaver  has  a  remarkably  strong  and  prominent 
zygoma.  A  peculiar  glandular  body  is  found  near  the  upper 
orifice  of  the  stomach,  full  of  cavities,  apparently  for  the  purpose 
of  secreting  mucus.  The  urethra  terminates  in  the  rectum,  thus 
constituting  a  kind  of  cloaca ;  a  structure  which,  as  we  shall  find, 
prevails  universally  in  birds.  The  direction  of  the  axes  of  the 
•orbits  is  upwards. 

958.  The  common  rat  has  no  coscum  ;  its  zygoma  has  its  con- 
vexity turned  downwards;  the  testes  are  capable  of  being 
retracted  within  the  abdomen.  A  similar  circumstance  occurs 
in  the  hamster,  the  squirrel,  and  the  guinea-pig. 


MAMMALIA.  387 

959.  The  mus  typhlus  is  remarkable  for  having  its  eye  covered 
over  with  the  common  integument  of  the  face,  which,  together 
with  the  hair  growing  on  it,  completely  intercept  light,  and  must 
destroy  the  use  of  the  eye  as  an  organ  of  vision. 

900.  Cheek  pouches  are  met  vi^ith  in  many  species  of  this 
genus ;  as  in  the  case  of  the  hamster  and  marmot.  In  the  ear  of 
the  latter  of  these  animals,  a  portion  of  bone  is  described  by  Cuvier 
as  passing  between  the  crura  of  the  stapes,  from  one  side  of  the 
fenestra  ovalis  to  the  other,  the  use  of  which  conformation  is 
entirely  unknown. 

901.  In  the  hare,  the  following  peculiarities  are  met  with. 
The  coronoid  process  of  the  lower  jaw  is  almost  entirely  wanting. 
The  transverse  processes  of  the  lumbar  vertebrae  are  remarkably 
large.  The  stomach  may  be  distinguished  into  two  portions, 
differing  in  the  structure  of  their  coats;  the  cardiac  portion  being 
lined  with  cuticle,  and  the  pyloric  division  having  the  usual  villous 
and  secreting  surface.  The  former  may  be  regarded  as  a  reser- 
voir for  the  food,  while  the  latter  is  the  part  which  performs  the 
function  of  digestion.  The  undigested  state  in  which  the  contents 
of  the  stomach  is  found  in  the  former,  and  its  altered  appearance 
in  the  latter,  corroborate  this  view  of  the  different  offices  of  these 
two  portions  of  the  stomach.  The  rabbit  agrees  with  the  hare 
in  this  conformation.  The  coecum  is  of  enormous  size  ;  it  extends 
to  a  length  which  is  greater  than  that  of  the  whole  animal ;  it  is 
curiously  convoluted,  and  is  lined  internally  with  a  peculiar  spiral 
fold  or  valve.  The  urinary  bladder  is  peculiarly  large  in  the 
hare. 

962.  The  retina  exhibits  very  distinct  and  beautiful  medullary 
strias,  which  pass,  for  the  most  part,  in  a  transverse  direction. 
The  glandula  Harderi  is  found  in  these  animals,  and  unites  itself 
with  the  proper  lacrymal  gland,  but  is  distinguishable  by  its  whiter 
colour.  Both  the  hare  and  the  rabbit  have  a  slit,  opening  into 
the  lacrymal  canal,  which  serves  as  a  substitute  for  the  puncta 
lacrymalia.  Sebaceous  sinuses  exist  on  the  outer  side  of  the 
upper  jaw,  near  the  nasal  bones  ;  whence  a  large  quantity  of  a 
viscid  adipose  substance  is  secreted.  Cavities  are  also  formed 
in  the  groins,  called  by  Pallas,  antra  inguinalia,  which  contain  a 
strongly  odorus  substance  prepared  by  the  neighbouring  subcuta- 
neous  glands. 

11.    Tardigrada. 

963.  The  tardigrade  mammalia  are  distinguished  by  having 
the  same  peculiar  distribution  of  the  arteries  of  the  limbs  which 
we  have  already  noticed  in  the  lemur  tardigradus.  They  possess 
neither  coecum  nor  gall-bladder.  The  stomach  of  the  sloth  is 
complicated  in  its  structure,  being  divided  into  several  pouches  ; 


388  COMPARATIVE    PHYSIOLOGY. 

the  intestinal  canal  is  very  short ;  there  is  also  at  its  extremity 
an  approach  to  the  structure  of  the  cloaca  of  birds,  inasmuch  as 
the  rectum  and  urethra  have  a  common  termination.  The 
zygoma  is  furnished  with  a  large  descending  process,  which 
comes  from  the  os  mate. 

964.  The  two-toed  sloth  (bradypus  didactylus)  has  twenty- 
three  ribs  on  each  side.  We  have  already  noticed  the  apparent 
anomaly  presented  by  the  three-toed  sloth  (the  bradypus  tridac- 
tylus),  in  its  seeming  to  possess  nine  instead  of  seven  cervical 
vertebrae ;  this  appearance  being  given  to  the  two  last  of  these 
vertebrae,  which  are,  in  fact,  dorsal,  by  the  ribs  which  are 
attached  to  them  being  very  short,  and  rudimental  in  their  con- 
formation (see  §  911).  In  the  ant-eater  and  manis,  which  belong 
to  Cuyier's  family  of  the  edentata,  the  six  last  vertebrae  of  the 
neck  are  anchylosed  or  united  so  as  to  form  only  one  bone. 

12.   Monotremata. 

965.  The  singular  animals  which  compose  this  family  of  mam- 
malia, instituted  by  M.  Geoffrey,  are  all  inhabitants  of  the  con- 
tinent of  Australia,  so  fertile  in  extraordinary  productions  in  every 
department  of  natural  history.  They  are  included  in  the  genus 
ornithorhyncus,  and  are  distinguished  into  the  three  species  of 
paradoxus,  histrix,  and  setosus. 

966.  Although  they  are  not  furnished  with  abdominal  pouches 
like  the  kangaroo  and  other  marsupial  animals,  yet  they  are 
provided  with  two  bones  corresponding  in  their  position  to  the 
marsupial  bones,  already  described  (§  952,)  as  attached  to  the 
bones  of  the  pubis,  and  supporting  the  abdominal  viscera.  The 
number  of  ribs  in  the  ornithorhyncus  is  seventeen.  Pouches 
exist  in  the  cheek  of  the  animal.  The  bill,  shaped  like  that  of  the 
duck,  is  abundantly  furnished  with  nerves,  chiefly  from  the  second 
branch  of  the  fifth  pair.  Its  teeth  have  no  fangs  which  sink  into 
the  jaw,  as  in  most  quadrupeds,  but  are  merely  imbedded  in  the 
gum,  and  are  very  peculiar  in  their  shape.  In  the  ornithorhyncus 
paradoxus,  there  is  one  on  each  side  of  either  jaw  ;  it  consists  of 
a  horney  substance  of  an  oblong  shape,  flattened  at  the  surface, 
and  adhering  to  the  gum.  There  are  likewise  two  horney  pro- 
cesses at  the  back  of  the  tongue,  which  are  directed  forwards, 
and  prevent  the  food  from  passing  into  the  throat  before  it  has 
been  sufficiently  masticated.  The  tongue  is  very  short,  not  an 
inch  long,  and  the  moveable  portion  not  half  an  inch  ;  its  surface 
is  beset  with  long  conical  papilla.  The  ornithorhyncus  hystrix 
has  six  transverse  rows  of  pointed  horny  processes  at  the  back 
of  the  palate,  and  about  twenty  similar  teeth  on  the  corresponding 
part  of  the  tongue.     The  intermaxillary  bones  are  of  a  very 


MAMMALIA.  389 

singular  shape,  consisting  of  two  hooked  pieces  joined  together 
at  their  bases. 

The  stomach  of  the  ornithorhyncus  hystrix  is  lined  with  cuticle, 
furnished  at  the  pyloric  extremity  with  sharp  horny  papillge. 
There  is  no  valve  of  the  colon,  nor  is  there  any  coecum,  although 
we  find  an  appendix  vermiformis.  They  possess  a  cloaca  at  the 
termination  of  the  rectum,  as  in  birds. 

967.  Sir  Everard  Home  denied  the  existence  of  mammae  in 
the  female  ornithorhyncus  ;  but  these  glands  have  been  distinctly 
delineated  by  Meckel,  and  described  by  him  as  being  largely 
developed.  In  a  paper  since  read  to  the  Royal  Society,  Sir 
Everard  Home  again  asserted  that  further  inquiry  had  convinced 
him  of  the  non-existence  of  these  glands  ;  but  in  a  paper  subse- 
quently read  to  that  learned  body,*  Mr.  Griffin  describes  the 
mammae  of  the  ornithorhyncus  paradoxus  as  considerable  glands, 
which  occupy  the  greater  part  of  the  under  surface  of  the  animal, 
and  have  numerous  excretory  ducts  perforating  the  skin  in  two 
circumscribed  places,  but  not  forming  any  elevations  analogous 
to  nipples.  This  subject  has,  since  that  period,  been  investigated 
with  great  care  by  Mr.  Owen,f  who  found  the  structure  to  cor- 
respond very  exactly  with  the  account  given  by  Meckel,  and  he 
is  accordingly  led  to  regard  them  as  real  mammee.  The  falx, 
as  well  as  the  tentorium,  contains  a  plate  of  bone.  The  external 
auditory  passage  is  very  long  and  tortuous,  and  there  are  only 
two  ossicula  in  the  internal  ear.  A  singular  kind  of  clavicle  is 
found  in  the  skeleton  of  these  animals,  common  to  both  the  fore 
extremities,  and  situate  in  front  of  the  ordinary  clavicles,  bearing 
some  analogy  to  the  furcular  bone  of  birds.  The  conformation 
of  the  ribs  also  exhibits  an  approach  to  that  of  birds.  Each  rib 
consists  of  two  pieces  of  bone  ;  a  longer  one  joined  to  the  spine, 
and  a  shorter  connected  with  the  sternum ;  the  two  being  united 
by  an  intermediate  cartilage. 

13.  Pachydermata. 

968.  In  this  natural  family  of  animals,  which  was  established 
hy  Storr,  in  his  Prodromus  Methodi  Animalium,  the  elephant  first 
claims  our  notice.  In  addition  to  the  thick  integument  common 
to  all  the  animals  of  this  tribe,  we  find  that  remarkable  organ, 
the  proboscis,  which  is  a  prolongation  of  the  nose,  formed  of  a 
double  cylindrical  tube,  extremely  flexible  in  all  directions,  en- 
dowed with  exquisite  sensibility,  and  terminating  in  an  appendix 
very  much  resembling  a  finger,  all  the  functions  of  which  it  is 
capable  of  performing.     The  motions  of  this  admirable  organ 

*  December  15,  1831. 

f  Philosophical  Transactions  for  1832,  p.  517.     See  also  his  paper  in  the 
Transactions  for  1834,  p.  333. 

33* 


390  COMPARATIVE   PHYSIOLOGY. 

are  executed  by  an  infinite  number  of  muscular  fibres,  collected 
into  small  bundles,  which  pass  in  a  great  variety  of  directions, 
and  are  continually  interlaced  with  one  another,  so  as  to  be 
adapted  to  the  performance  of  every  kind  of  movement.  The 
enormous  tusks  which  are  given  to  the  animal  as  formidable 
weapons  of  offence,  are  merely  developments  of  incisor  teeth, 
])roceeding  from  the  inter-maxillary  bones  in  the  upper  jaw,  and 
which  on  issuing  from  the  mouth  are  incurvated  upwards. 

969.  That  part  of  the  cranium  which  corresponds  to  the 
frontal  sinuses  is  enormously  enlarged  ;  the  two  tables  of  the 
skull  being  separated  to  a  considerable  distance  from  one  another, 
the  intermediate  space  being  occupied  by  a  vast  number  of  cells, 
which  are  full  of  air,  and  communicating  with  .the  throat  by 
means  of  the  Eustachian  tube.  Camper  has  very  ably  pointed 
out  the  advantages  resulting  from  this  structure,  by  the  increase 
of  surface  it  affords  for  the  attachment  of  the  great  muscles  of 
the  lower  jaw,  neck,  and  proboscis,  and  for  the  augmentation  of 
their  mechanical  power.  The  frontal  and  parietal  bones  become 
united  at  a  very  early  period  with  all  the  other  parts  of  the 
cranium,  so  as  to  form  a  bony  cavity  in  which  no  trtice  of  su- 
tures can  be  discerned.  The  tympanic  bone,  however,  is  distinct 
from  the  temporal.  The  optic  foramina  commence  from  a  single 
canal,  which  receives  the  two  optic  nerves-  A  rudiment  only  of 
the  nasal  bones  is  observable ;  and  the  same  remark  is  also 
applicable  to  the  ossa  unguis,  or  lacrymal  bones  ;  neither  can  we 
trace  the  existence  of  any  lacrymal  gland,  or  lacrymal  sac,  or 
any  passage  for  the  tears  into  the  nose.  The  foramen  ovale  in 
the  base  of  the  cranium  is  very  large.  Between  the  arched  sides 
of  the  upper  part  of  the  cranium,  a  broad  and  deep  depression  is 
met  with,  having  a  small  longitudinal  crest  in  the  bottom. 

970.  Between  the  eye  and  the  orifice  of  the  external  ear,  a 
gland  of  large  size  is  situate,  occasionally  secreting  a  brown 
liuid,  which  oozes  out  through  an  opening  in  the  skin.  There 
are  twenty  ribs  on  each  side ;  and  there  appear  to  be  only  three 
lumbar  vertebrae.  The  ligamentum  nuchge  is  of  great  size  and 
strength,  for  it  has  to  support  the  enormous  weight  of  the  head 
with  its  ponderous  tusks  and  proboscis.  The  articulation  of  the 
thigh  bone  with  the  pelvis,  is  destitute  of  the  ligamentum  teres, 
which  is  found  in  almost  all  other  quadrupeds.  The  toes  are  five 
in  number,  but  they  are  almost  concealed  by  the  thickness  of  the 
skin  of  the  foot  in  which  they  are  encased.  The  condyles  of  the 
lower  jaw  are  simply  rounded  eminences.  The  form  and  structure 
of  the  teeth  are  very  peculiar,  and  afford  distinctive  characters 
of  the  different  species  of  the  elephants,  which  belong  more  pro- 
perly to  natural  history.  In  addition  to  the  usual  component 
parts  of  bones  and  of  enamel,  a  third  is  superadded,  called  the 
crusta  petrosa^  which  fills  up  the  interstices,  left  by  the  duplications 


MAMMALIA.  391 

of  the  enamel.  The  ivory  which  composes  the  tusks  is  exceed- 
ingly dense,  and  diflers  considerably  in  its  structure  from  the 
ordinary  bone  of  other  teeth.  It  is  distinguished  by  the  curved 
lines  which  pass  in  different  directions  from  the  centre  of  the 
tusk,  forming  by  their  decussation,  a  regular  arrangement  of 
curvilinear  lozenges.  The  tusk  is  constructed  by  the  successive 
depositions  of  osseous  matter  from  within,  being  secreted  from 
the  outer  surface  of  the  vascular  ]5ulp,  which  occupies  the  central 
part  of  the  growing  tusk.  Hence,  iron  balls,  fired  at  the  animal, 
have  been  known  to  penetrate  the  latter  soft  portion,  and  to  re- 
main fixed  in  the  interior  of  the  tusk,  till  they  were  completely 
covered  over,  and  imbedded  in  the  successive  depositions  of 
ivory. 

971.  The  stomach  is  simple  in  its  structure;  the  intestines  are 
voluminous,  the  coecum  of  great  size,  and  the  colon  large,  long, 
and  divided  into  cellular  compartments.  There  is  no  gall-bladden 
The  ductus  choledochus  forms  a  pouch  between  the  coats  of 
the  intestines,  as  it  does  in  the  cat,  for  the  reception  of  the  pan- 
creatic duct. 

972.  The  snout  of  the  tapir  bears  a  slight  resemblance  to  the 
proboscis  of  the  elephant;  being,  although  much  shorter,  ex- 
tremely mobile,  and  provided  with  a  very  complex  arrangement 
of  muscles. 

973.  The  rhinoceros  is  furnished  with  a  rough  and  slightly 
elevated  surface  of  the  large  nasal  bones,  consolidated  into  one 
bone,  for  the  attachment  of  the  horn  which  is  supported  upon  it. 
Such,  at  least,  is  the  structure  in  the  one-horned  rhinoceros  ;  in  the 
two-horned  species  it  is  the  front  horn  to  which  this  description 
applies ;  for  the  posterior  horn  rests  on  a  similar  process  of  the 
OS  frontis.     Like  the  elephant,  the  rhinoceros  has  no  gall-bladder. 

974.  In  the  hog  we  also  meet  with  a  considerable  development 
of  the  frontal  sinuses.  The  molar  glands  are  large,  and  their 
openings  very  conspicuous.  There  are  two  considerable  mem- 
branous bags  in  the  throat,  situate  above  and  in  front  of  the 
ligaments  of  the  glottis.  Two  small  flat  bones  are  found  at  the 
base  of  the  heart,  at  the  origin  of  the  aorta  from  the  left  ventricle. 
Their  use  has  been  supposed  to  be  that  of  giving  support  to  the 
valves  of  the  aorta. 

975.  The  peccari,  or  Mexican  musk-hog,  has  a  remarkable 
gland  situate  in  the  back,  near  the  sacrum;  it  is  composed  of 
several  lobules,  the  ducts  of  which  unite  into  one  canal,  which 
passes  through  the  skin,  and  pours  out  a  secretion  having  a  scent 
similar  to  musk.  A  singular  dilatation  is  often  met  with  in  the 
aorta  of  this  animal,  as  if  it  were  affected  with  aneurism. 


392 


COMPARATIVE    PHYSIOLOGY. 


14.  Solipeda. 


976.  This  family  comprehends  the  horse,  ass,  zebra,  and  quagga. 
The  great  interest  attached  to  all  that  relates  to  the  horse,  from 
its  utility  to  man,  has  occasioned  its  anatomy,  the  study  of  which 
is  the  foundation  of  the  veterinary  art,  to  be  cultivated  with 
peculiar  zeal.  The  principal  circumstances  worthy  of  notice  in 
the  osteology  of  this  animal  art  the  following.  As  is  the  case 
with  most  quadrupeds  whose  necks  are  very  long,  the  cervical 
vertebrae  have  very  short  spinous  processes.  The  dorsal  vertebrae, 
the  number  of  which  of  course  corresponds  with  that  of  the  ribs, 
being  eighteen,  and  sometimes  nineteen,  have,  on  the  contrary, 
very  large  and  broad  spinous  processes.  The  space  from  the 
first  to  the  eighth  vertebrae,  is  called  the  loithers,  against  which 
the  upper  part  of  the  shoulder  rests.  There  are  six  lumbar  vertebras, 
having  strong  spinous,  and  also  broad  and  long  transverse  processes. 
Large  lateral  processes  also  extend  from  the  sacrum,  which  is 
composed  of  five  consolidated  portions ;  and  the  united  spinous 
processes  of  these  are  likewise  exceedingly  prominent.  The  tail 
is  formed  of  eighteen  cylindrical  pieces,  which,  towards  the 
extremity,  have  nearly  the  softness  of  cartilage. 

977.  The  true  ribs  are,  on  each  side,  eight  in  number,  the 
remaining  ten  or  eleven  being  joined  to  the  sternum  by  cartilage. 
The  sternum  is  composed  originally  of  seven  pieces  of  bone  united 
into  one.  Its  anterior  extremity  is  sharp-pointed,  like  the  prow  or 
keel  of  a  ship.  In  the  pelvis  of  the  horse,  denominated  the  haunch, 
we  find  the  ilium,  or  hip-bone,  extended  in  three  directions,  above, 
below,  and  behind,  forming  three  large  processes,  for  the  attach- 
ment of  the  strong  muscles  which  surround  the  hip  joint.  The 
ischium  is  much  extended,  formiing  a  strong  process  posteriorly 
for  a  similar  purpose.  This  elongation  of  the  ischium  has  been 
termed,  from  its  figure,  the  processus  triquetrus  ischii.  By  remov- 
ing the  point  of  attachment  of  the  muscles  to  a  greater  distance 
from  the  axis  of  motion,  it  gives  them  the  mechanical  advantage 
of  acting  by  a  long  lever.  The  symphysis  of  the  pubis  (or  the 
junction  of  the  bones  of  that  name)  is  remarkable  for  its  depth, 
thus  aflfording  an  extensive  surface  for  the  attachment  of  muscles. 

978.  The  bones  of  the  extremities  of  the  horse  are  constructed 
on  the  same  general  model  as  the  human,  though  varying  much 
in  the  details  of  their  form  and  relative  proportions ;  and  some 
parts  only  appearing  in  an  imperfect  or  rudimental  state.  The 
scapula  is  of  an  oblong  triangular  shape,  considerably  narrower 
and  longer  than  the  same  bone  in  the  human  skeleton,  and  exhi- 
biting only  faint  traces  of  the  acromion  and  coracoid  processes. 
Its  axis  is  nearly  in  the  same  line  with  the  os  humeri,  which  latter 
bone  is  very  short,  and  scarcely  descends  below  the  line  of  the 
chest,  and  possesses  scarcely  any  rotatory  motion  on  the  scapula. 


MAMMALIA. 


393 


The  radius  and  ulna  are  consolidated  together ;  the  olecranon  is 
much  elongated.  The  carpus,  or  as  it  is  vulgarly  called,  the 
knee,  of  the  horse,  is  composed  of  seven,  or  sometimes  eight, 
small  bones,  disposed  as  in  the  human  carpus,  in  two  rows; 
though  with  respect  to  their  individual  form,  they  have  but  little 
resemblance  to  the  latter. 

979.  That  part  of  the  skeleton  which  corresponds  to  the  meta- 
carpus is,  in  the  horse,  consolidated  into  a  single  bone  termed  the 
shank,  or  canon  hone,  to  which  are  united  behind,  and  on  the 
side,  two  much  shorter  and  very  slender  bones,  called  the  styloid, 
or  splint  hones,  frequently  found  consolidated  with  the  canon 
bone  by  ossific  union.  It  is  only  the  latter,  or  principal  bone, 
that  is  articulated  with  the  next,  or  pastern  hone,  which  corres- 
ponds with  the  first  phalanges  of  the  fingers,  and  may  be  regarded 
as  the  consolidation  of  these  five  bones  into  one.  In  like  manner, 
the  second  phalanges  are  consolidated  in  the  horse  into  the  next 
bone  of  the  foot,  which  is  termed  the  coronet  hone,  and  which  is 
articulated  by  a  divided  condyle  with  the  coffin  hone,  of  which 
we  shall  presently  speak.  Before  proceeding,  however,  we  must 
notice  two  or  three  small  rounded  bones  placed  at  the  back  of 
the  pastern  joint,  (between  that  and  the  shank  bone)  which  cor- 
respond in  their  office  to  sesamoid  bones,  and  which  have 
accordingly  received  that  appellation. 

980.  The  coffin  bone  corresponds  in  situation  to  the  third 
phalanx  of  the  fingers.  It  supports  the  single  hoof;  from  which 
this  family  of  mammaHa  derive  their  characteristic  name.  Con- 
nected with  this  is  a  small  bone,  called  the  shuttle  hone. 

981.  In  the  posterior  extremity  we  find  a  very  similar  arrange- 
ment of  bones.  The  thigh  bone  is  unusually  short,  scarcely  extend- 
ing beyond  the  trunk  of  the  body,  when  surrounded  by  its  muscles. 
The  glutsei  muscles,  and  especially  the  glutseus  medius,  are  parti- 
cularly powerful  in  their  action  "for  extending  the  thigh  back- 
wards, and  performing  the  motion  necessary  for  kicking.  There 
is  a  process  in  this  bone  of  the  horse  which  is  not  observed  at  all 
in  the  human  os  femoris  ;  it  is  a  strong  curved  spine,  situate  on 
the  outside,  opposite  to  the  lesser  trochanter.  It  has  been  termed 
the  processus  recurvatus  femoris. 

982.  The  patella  of  the  horse  Is  large,  thick,  and  very  promi- 
nent. From  the  tihia  there  arises  a  small  spinous  process,  w^hich 
may  be  considered  as  the  rudiment  of  a  fibula.  The  tarsus,  or 
hock,  is  composed  of  six  or  seven  bones,  and  forms  a  very  obtuse 
angle  with  the  tibia,  when  the  horse  has  his  foot  to  the  ground. 
The  astragalus  differs  from  the  human  bone  of  that  name,  by 
having  two  very  large  and  prominent  condyles.  The  metatarsal 
bones  correspond  in  every  respect  with  those  of  the  carpus  already 
described. 

983.  In  the  skull  of  the  horse  we  mav  observe  that  the  tern- 


394 


COMPARATIVE    PHYSIOLOGV. 


poral  bone  is  divided  by  a  suture  into  the  squamous  and  tympanic 
portions.  The  occipital  bone  has  a  deep  depression  in  the  middle, 
where  the  cervical  ligament  is  attached.  The  antrum  maxillare 
and  turbinated  bones  are  of  great  size.  The  lower  jaw-bone  is 
also  very  large,  and  presents  a  very  extended  surface  for  the 
attachment  of  muscles. 

The  horse  is  provided  with  a  large  salivary  apparatus  of  glands. 
Its  stomach  is  divided  into  two  portions ;  the  first  of  which,  next 
to  the  ossophagus,  is  lined  with  a  cuticular  membrane  which  ter- 
minates in  a  loose  expansion,  supposed  to  have  the  office  of  a 
valve,  and  to  prevent  the  possibility  of  the  animal's  vomiting. 
There  are  generally  found  adhering  to  its  coats  a  great  number 
of  the  larvae  of  the  oestrus  equi,  and  the  oestrus  hsemorrhoidahs, 
called  in  common  language,  hotts.  The  intestinal  canal  is  of 
great  length,  the  large  intestine  alone  being  twenty-four  feet  in 
length.  The  colon  is  very  capacious,  and  divided  into  cellular 
compartments.  The  liver  is  large,  divided  by  deep  indentations 
into  lobes,  and  unprovided  with  a  gall-bladder. 

984.  The  peculiar  sound  produced  in  neighing  is  ascribed  to 
the  presence  in  the  trachea  of  a  delicate  membrane,  attached  by 
its  middle  to  the  thyroid  cartilage,  and  of  which  the  two  extremi- 
ties pass  along  the  external  margins  of  the  rim  a  glottidis.  The 
Eustachian  tube  opens,  not  immediately  over  the  larynx,  but  into 
a  sac  peculiar  to  this  tribe  of  animals,  situate  on  the  lateral  parts 
of  the  lower  jaw ;  and  these  cavities  then  open  by  a  long 
fissure,  furnished  with  a  cartilaginous  valve,  into  the  pharynx. 

985.  The  eye  of  the  horse  presents  a  remarkably  beautiful  and 
delicate  structure  in  the  folds  of  the  internal  membrane  of  the 
corpus  ciliare.  The  pupil  is  oblong,  the  superior  margin  of  the 
iris  having  a  fringed  appearance. 

15.  Ruminantia. 

986.  The  anatomy  of  the  ruminant  family  of  quadrupeds,  which 
comprises  so  many  of  those  animals  that  man  has  domesticated 
and  rendered  subservient  to  his  most  urgent  wants,  has  also  very 
strong  claims  on  our  attention. 

987.  In  their  skeleton  they  correspond  very  closely  with  the 
horse,  of  which  we  have  already  given  so  detailed  a  description. 
The  principal  differences  are  observable  in  the  terminal  bones  of 
the  extremities,  each  limb  presenting  us  with  two  hoofs,  instead 
of  one,  and  a  corresponding  division  of  the  metatarsal  bones  and 
phalanges  into  two.  On  the  other  hand,  the  slender  traces  of  a 
fibula  met  with  in  the  horse,  disappear  in  the  ox  and  other  animals 
of  this  tribe. 

988.  The  whole  track  of  the  alimentary  canal  in  these  animals 
presents  us  with  objects  of  interest.     The  tongue  is  covered  with 


MAMMALIA.  395 

a  thick  cuticle,  provided  with  pointed  papillas,  which  being  directed 
backwards,  are  fitted  for  laying  firm  hold  of  the  grass,  and  tear- 
ing it  up  from  the  roots.  The  salivary  glands  are  extremely 
large  ;  the  coats  of  the  oesophagus  particularly  strong  and  mus- 
cular, in  subservience  to  the  function  of  rumination  peculiar  to 
this  tribe.  The  organs  provided  for  digestion  are  more  compli- 
cated than  in  any  of  the  animals  we^have  yet  considered.  There 
are  no  less  than  four  cavities  which  have  been  regarded  as  per- 
forming the  otfice  of  stomachs.  The  first  is  the  paunch,  which 
is  a  capacious  reservoir,  abundantly  supplied  with  secretion  from 
its  coats,  which  are  beset  with  numerous  flattened  papillce.  The 
second  is  the  lioney-comh  stomach,  so  named  from  the  reticulated 
appeax'ance  of  its  inner  membrane,  the  folds  of  which  are  dis- 
posed in  polygonal  lines,  somewhat  resembling  the  hexagonal 
margins  of  the  cells  of  the  honey-comb.  The  third  stomach, 
which  is  the  smallest,  is  termed  the  manyplies,  and  contains  a 
greatnumber  of  broad  folds,  or  duplicatures  of  its  inner  membrane, 
which  have  been  compared  to  the  leaves  of  a  book.  The  fourth, 
or  the  reed,  has  a  pyriform  shape,  an  internal  villous  coat,  and  a 
structure  altogether  analogous  to  that  of  the  simple  stomachs  of 
carnivorous  animals.  It  terminates  in  the  beginning  of  the  intes- 
tinal canal.  A  groove  extends  from  the  termination  of  the  ceso- 
phagus  along  the  edge  of  the  three  first  stomachs,  at  the  part 
where  they  communicate  together ;  the  edges  of  this  groove  are 
thick,  so  as  to  admit,  when  brought  in  close  contact,  of  forming  a 
canal  for  the  direct  communication  of  the  oesophagus  with  any 
one  of  these  four  stomachs. 

989.  The  grass  which  the  animal  takes  into  the  mouth  under- 
goes but  a  small  degree  of  mastication,  and  passes,  on  being 
swallowed,  into  the  paunch,  where  it  undergoes  maceration,  and 
is  transferred,  by  small  portions  at  a  time,  into  the  honey-comb, 
or  second  stomach,  which  serves  to  perform  an  auxiliary  office 
to  the  first.  Thence  it  is  sent  up  again  directly  through  the 
oesophagus  into  the  mouth,  for  the  purpose  of  undergoing  a  second 
and  more  deliberate  mastication,  which  the  animal  perform.s 
when  reposing,  and  from  which  it  appears  to  enjoy  considerable 
pleasure.  After  being  thus  ruminated  it  is  again  swallowed,  and 
the  sides  of  the  groove  being  brought  into  contact,  so  as  to  con- 
stitute a  canal,  and  exclude  all  passage  into  the  first  or  second 
stomachs,  it  passes  directly  into  the  third  stomach  ;  whence,  after 
having  been  subjected  to  the  further  action  of  the  secretions  of 
that  organ,  it  is  transferred  to  the  fourth  or  last  stomach,  where 
the  process  of  digestion  is  completed.  Liquids  drunk  by  the 
animal  pass  at  once  into  the  second  stomach,  and  assist  in  the 
maceration  of  its  contents.  But  the  milk  taken  by  the  calf, 
requiring  to  be  neither  macerated  nor  ruminated,  is  conveyed 
directly  from  the  ojsophagus  into  the  fourth  stomach. 


396  COMPARATIVE    PHYSIOLOGY 

990.  The  biliary  organs  present  us,  in  horned  cattle,  with 
numerous  hepato-cystic  ducts,  conveying  the  bile  immediately 
from  the  liver  to  the  gall-bladder,  which  cyst  is  found  in  all  the 
animals  of  this  order,  though  it  is  absent  in  the  horse.  The 
urinary  bladder  is  particularly  large.  In  Hke  manner,  as  we  found 
in  the  pig,  two  small  bones  are  met  with  also  in  ruminants,  at  the 
origin  of  the  aorta  ;  and  the  same  purpose  has  been  assigned  to 
them  as  in  the  former  instance.  In  the  stag,  these  have  been 
called  the  hones  of  the  heart. 

991.  The  internal  carotid  artery,  at  its  entrance  into  the 
cranium,  is  suddenly  subdivided  into  numerous  branches,  which 
are  variously  contorted,  and  afterwards  re-united  at  the  basis  of 
the  brain.  The  intention  of  this  curious  structure,  which  has 
been  termed  the  rete  mirabile,  appears  to  be  to  diminish  the 
impetus  with  which  the  blood  would  otherwise  be  forced  into 
the  arteries  distributed  to  the  brain ;  a  force  which  would  be 
increased  by  the  effect  of  gravity  when  the  animal  stooped  in 
grazing.  The  frontal  sinus,  and  other  parts  connected  with  the 
sense  of  smell,  are  much  developed.  The  lacrymal  bones  and 
ossa  nasi  are  of  considerable  size.  The  tapetum  is  particularly 
conspicuous  in  the  eyes  of  ruminants.  One  or  two  additional 
small  bones  are  found  among  the  ossicula  auditus.  The  mastoid 
cells  are  numerous,  and  in  the  arrangement  of  their  compartments 
somewhat  resemble  a  ripe  poppy  head.  In  the  ox  and  the  sheep, 
the  superior  ligam.ent  of  the  glottis,  as  well  as  the  ventricles  of 
the  larynx,  are  absent. 

992.  Ruminant  animals  are  distinguished  into  two  tribes,  the 
first  consisting  of  those  which  are  without  horns  ;  the  second,  of 
those  provided  with  horns.  Of  the  former,  the  camel  is  remark- 
able for  the  great  expansion  of  the  hoof,  which  adapts  it  for 
treading  upon  sand.  It  has  seven  lumbar  vertebrae.  A  pecuhar 
moveable  bag,  glandular  in  its  structure,  exists  behind  the  palate, 
probably  designed  for  the  lubrication  of  the  throat ;  it  has  re- 
ceived the  name  of  bursa  faucium.  Connected  with  the  paunch 
is  a  large  receptacle  divided  into  numerous  cells,  for  the  purpose 
of  holding  water,  as  in  a  natural  reservoir.  Hence,  when  a  camel 
dies  in  the  desert,  the  Arabs  open  the  stomach,  and  quench  their 
thirst  with  the  water  it  contains,  which  is  found  to  be  pure  and 
wholesome.  Like  the  horse,  it  has  no  gall-bladder.  It  has  no 
fibula  ;  but  this  latter  bone  is  met  with  in  the  musk,  which  is  also 
a  hornless  ruminant. 

993.  The  horned  ruminants  have  an  eminence  on  the  os  frontis 
for  supporting  the  horn.  This  process  is  in  the  stag  a  real  bone, 
remarkable  for  the  rapidity  of  its  growth,  which  is  annual,  and 
for  its  death  and  separation  from  the  skull  at  certain  periodic 
intervals.  The  osseous  bases  of  the  horns  of  the  ox,  the  sheep, 
the  goat,  and  the  antelope,  on  the  contrary,  are  permanent,  and 


MAMMALIA.  397 

are  invested  with  a  horny  covering,  which  has  a  structure  very 
different  from  bone.  The  camelopard,  or  giraffe,  on  the  other 
hand,  has  two  osseous  prominences,  which  remain  permanently 
covered  with  the  integuments,  and  are  even  surmounted  by  a 
tuft  of  hair.  But  the  details  relating  to  organs  so  external  as  the 
horns  fall  more  properly  within  the  province  of  natural  history. 

994.  The  rein  deer  has,  like  several  of  the  baboon  tribe,  large 
laryngealsacs  on  the  front  of  the  neck,  communicating  with  the 
larynx. 

995.  In  the  ox  and  sheep  the  spleen  is  remarkable  for  being  of 
a  distinctly  cellular  structure.     In  these  animals  we  find  a  great 
development  of  the  salivary  glands,  and  more  particularly  of  the 
submaxillary  gland,  which  extends  along  the  side  of  the  larynx  - 
quite  to  the  back  of  the  pharynx. 

16.  Cetacea. 

996.  From  the  consideration  of  the  quadrupeds  of  the  class 
mammalia,  we  pass  now  to  that  of  a  tribe  of  animals  which,  al- 
though warm-blooded  and  mammiferous,  are  formed  on  a  model 
adapting  them  for  inhabiting  the  water  ;  nature  having  bereft 
them  even  of  the  rudiments  of  hinder  extremities.  The  bones  of 
the  spine  are  continued,  without  being  interrupted  by  an  inter- 
posed pelvis,  into  the  vertebrse  of  the  tail,  which  terminates  in  a 
horizontal  fin.  The  head  and  trunk  are  united  by  a  neck,  so 
short  as  to  exhibit  scarcely  any  diminution  of  diameter,  and  con- 
taining cervical  vertebrse,  which  are  extremely  compressed,  and 
the  greater  number  of  which  are  consolidated  together  by  a  bony 
union.  The  superior  extremities  are  supported  by  bones,  which 
have  no  medullary  cavities,  and  which,  compared  with  the  ana- 
logous bones  of  quadrupeds,  are  much  shortened  and  compressed. 
They  do  not  admit  of  motion  amongst  themselves,  and  being 
enveloped  by  a  tendinous  membrane,  are  reduced  to  the  office  of 
fins.  The  internal  organs  correspond,  however,  with  that  of 
other  mammaUa.  Cetacea  breathe  by  means  of  lungs,  their 
circulation  is  double,  and  they  are  warm-blooded.  The  females 
are  viviparous,  and  are  provided  with  mammee  for  the  nourish- 
ment of  their  young. 

997.  The  necessity  of  occasionally  receiving  air  into  the  lungs, 
whilst  the  animal  is  generally  immersed  in  water,  renders  it  re- 
quisite that  a  provision  should  be  made  for  their  readily  rising  to 
the  surface  in  order  to  breathe.  Hence  the  movements  of  the 
tail  are  from  above  downwards  ;  hence  in  the  cachalot  and  other 
kinds  of  whale,  a  large  quantity  of  oil  is  accumulated  round  the 
head,  which  gives  greater  buoyancy  to  this  part  of  the  body. 
Hence,  also,  when  the  animal,  in  seizing  its  prey,  takes  into  the 
mouth  a  large  quantity  of  water,  there  is  a  necessity  of  getting 

34 


398  COMPARATIVE    PHYSIOLOGY. 

rid  of  it,  which  is  effected  by  its  transmission  into  a  sac  placed 
at  the  external  orifice  of  the  nasal  cavity,  whence  it  is  expelled 
with  great  force,  by  the  contraction  of  powerful  muscles,  through 
a  passage  which  conducts  it  to  the  top  of  the  head.  In  this  way 
are  produced  the  enormous  spouts  of  water  that  mark  the  track 
of  the  whale  on  the  surface  of  the  sea. 

998.  The  olfactory  organs  are  not  adapted  to  the  possession 
of  any  accurate  sense  of  smell,  being  furnished  neither  with 
turbinated  bones  nor  with  any  considerable  nerves.  The  larynx 
rises  in  a  pyramidal  form  into  the  posterior  part  of  the  nostrils, 
in  order  to  receive  the  air  from  those  passages,  and  convey  it  to 
the  lungs,  without  its  being  necessary  for  the  animal  to  extend 
more  than  the  end  of  the  snout  above  the  surface  of 'the  water. 
The  glottis  is  simple,  and  is  not  interrupted  by  any  projecting 
membranes. 

999.  The  stomach  is  composed  of  as  many  as  five,  or  some- 
times even  of  seven  distinct  pouches.  There  is  no  coecum  or 
appendix  vermiformis ;  and  the  gall-bladder  is  absent  in  the 
greater  number.  The  spleen  is  divided  into  a  number  of  small 
globular  lobes.  The  kidneys  are  conglomerate.  The  brain  is 
large,  and  its  hemispheres  much  developed.  The  tympanic  bone 
is  separated  from  the  rest  of  the  cranium,  adhering  to  it  only  by 
ligamentous  connexions.  There  is  no  external  air ;  the  stapes  is 
nearly  solid  ;  in  the  walrus  it  exhibits  no  perforation.  The  ossi- 
cula,  semicircular  canals,  and  other  parts  of  the  labyrinth  of  the 
internal  ear  are  remarkably  small.  The  external  meatus  is  carti- 
laginous, and  so  small,  that  its  external  orifice  in  the  dolphin  will 
only  just  admit  a  pin.  It  pursues  a  winding  course  through  the 
the  fat,  which  is  of  great  thickness,  until  it  reaches  the  tympanum. 
The  Eustachian  tube  opens  at  the  blowing  hole,  and  is  furnished 
with  a  valve  preventing  the  admission  of  the  water  which  the 
animal  expels  through  that  passage.  The  lacrymal  organs  are 
entirely  wanting ;  the  sclerotic  coat  of  the  eye  is  very  thick  at 
its  posterior  part,  so  that  although  the  eye-ball  has  exteriorly  a 
spherical  form,  the  figure  of  the  vitreous  humor  is  very  different; 
its  structure  at  the  back  of  the  eye  has  the  hardness  of  cartilage. 

1000.  In  many  parts  of  the  arterial  system  of  the  cetacea,  we 
find  reticular  plexuses,  or  convolutions  of  the  vessels,  the  pur- 
pose of  which  is  probably  to  serve  as  reservoirs  of  arterial 
blood,  for  the  use  of  the  system,  when  the  animal  is  long  under 
water. 

1001.  In  the  trichecus  manatus  borealis,  or  manati,  a  gland  of 
the  size  of  the  human  head  is  found  between  the  coats  of  the 
stomach,  near  the  oesophagus,  discharging,  on  pressure,  a  fluid 
resembling  the  pancreatic  juice. 

1002.  The  whale  is  remarkable  for  having,  in  place  of  teeth, 
an  apparatus  apparently  intended  for  filtration,  and  consisting  of 


BIRDS.  399 

plates  of  the  substance  called  whalehone,  descending  vertically 
into  the  mouth  from  the  lower  surface  of  the  upper  jaw,  into 
which  they  are  fixed  by  a  ligamentous  substance.  On  each  side 
their  number  amounts  to  three  or  four  hundred.  The  inner  edge 
of  each  plate  has  its  fibres  detached  so  as  to  form  a  kind  of 
fringe,  which  retains  the  small  fishes  and  mollusca  on  which  the 
animal  feeds.  The  lower  jaw  is  unprovided  with  any  similar 
appendages.  Although  there  are  no  teeth  in  the  upper  jaw,  yet 
an  intermaxillary  bone  is  still  present.  Rudiments  of  teeth  exist  in 
the  interior  of  the  lower  jaw  before  birth,  lodged  in  deep  sockets, 
and  forming  a  row  on  each  side.  The  development  of  these  im- 
perfect teeth,  however,  proceeds  no  further,  and  they  disappear 
at  an  early  period.  The  tongue,  which  is  supported  by  an  os 
hyoides  of  singular  shape,  is  very  thick  and  fleshy.  The  oesopha- 
gus is  exceedingly  narrow.  The  stomach  is  complicated  in  its 
structure.  The  intestinal  canal  is  of  considerable  length,  and 
contains  a  great  number  of  longitudinal  folds.  There  is  a  short 
coecum.  The  mesenteric  glands  contain  large  spherical  cavities, 
into  which  the  trunks  of  the  lacteals  open,  and  where  the  chyle 
is  probably  blended  with  secretions  proper  to  those  cavities.  The 
eye  is  extremely  small  in  comparison  with  the  size  of  the  animal; 
and  it  occupies  but  a  small  portion  of  the  orbit. 


Sect.  II. —  Comiparative  Physiology  of  Birds. 
1.   General  Description. 

1002.  The  whole  of  this  class  of  animals  exhibits  great  unifor- 
mity in  its  comparative  anatomy ;  insomuch  that  the  whole  may 
easily  be  comprised  in  one  general  description.  The  structure 
of  every  part  of  the  frame  of  birds  is  adapted  to  facilitate  rapid 
progression  through  the  air ;  for  which  purpose  the  anterior 
extremities  are  converted  into  wings,  and  are  not  employed  in 
any  other  action.  The  support  of  the  body  when  the  animal  is 
not  flying,  is  entrusted  solely  to  the  posterior  extremities ;  so  that 
birds  are,  strictly  speaking,  bipeds.  Hence  we  may  trace  some 
degree  of  approximation  to  the  human  structure  in  the  conforma- 
tion of  the  skeleton. 

1003.  The  bones  are  dense  in  their  texture,  but  are  at  the  same 
time  rendered  light  by  having  large  cavities,  occupied,  not  with 
marrow,  as  in  the  mammalia,  but  with  air.  There  is  a  smaller 
proportion  of  cartilaginous  to  osseous  structure  in  the  skeleton  of 
birds  than  in  that  of  quadrupeds. 

1004.  The  neck  of  birds  being  required  to  be  very  flexible,  we 
find  the  cervical  vertebrae  very  numerous,  and  freely  moveable 
upon  one  another.     The  swan  has  twenty-three  cervical  vertebrae. 


400  COMPARATIVE    PHYSIOLOGY. 

Those  of  the  back,  on  the  other  hand,  are  perfectly  fixed  and 
immoveable,  then'  spmous  processes  being  large  and  often  united 
by  osseous  substance,  so  as  to  preclude  the  possibility  of  any 
relative  motion.  As  the  ribs  occupy  the  whole  of  the  sides  of 
the  trunk,  there  are  properly  no  lumbar  vertebrae.  The  os 
coccygis  is  short  and  compressed ;  and  can  scarcely  be  regarded 
as  a  proper  tail,  although  it  affords  support  to  the  long  feathers 
which  constitute  what  is  usually  called  the  tail  of  birds.  The  pelvis 
consists  almost  entirely  of  a  broad  os  innominatum,  the  lateral 
portions  of  which  are  widely  separated,  in  order  to  admit  of  space 
for  the  development  of  the  eggs ;  and  for  the  same  reason  the 
two  ossa  pubis  do  not  join  to  form  a  symphysis,  biit  are  at  a 
considerable  distance  from  one  another.  The  exceptions  to  this 
general  rule  will  be  noticed  afterwards. 

1005.  The  number  of  true  ribs  never  exceeds  ten  pair;  the 
false  ribs  are  numerous,  and  directed  forwards.  Those  which 
occupy  the  middle  of  the  body  are  distinguished  by  a  flat  process, 
directed  upwards  and  backwards.  The  sternum  is  composed  of 
five  pieces,  and  is  of  great  size  and  strength.  From  the  middle 
of  its  lower  surface  there  rises  a  sharp  process,  or  spine,  resem- 
bling the  keel  of  a  ship,  and  evidently  adapted  to  accommodate 
the  large  and  powerful  pectoral  muscles,  which  take  their  rise 
from  this  part  of  the  chest,  and  which  act  in  depressing  the  wings. 
The  bones  which  connect  the  wings  to  the  trunk  are  apparently 
three  in  number;  the  coracoid  process  of  each  scapula  being 
distinct  and  largely  developed  bones,  having  the  semblance  of 
ordinary  clavicles,  whilst  the  real  clavicles  are  consolidated  into 
a  single  bone,  denominated  the  filrcular  bone,  from  its  resemblance 
to  a  fork,  and  which  in  the  fowl  is  better  known  by  the  name  of 
the  merry-thought.  Its  extremities  rest  on  two  strong  processes 
of  the  scapula.  Many  anatomists,  considering  the  coracoid  as  the 
true  clavicles,  have  regarded  the  furcular  bone  as  an  additional, 
or  supplementary  clavicle,  corresponding  to  the  coracoid  apophysis. 

1006.  The  bones  of  the  wing  are  analogous  in  their  divisions 
and  distribution  to  those  of  the  upper  extremity  in  man :  there 
being  a  humerus,  radius,  and  ulna  ;<  tvv^o  carpal  bones  ;  and  two 
metacarpal  bones,  generally  consolidated  into  one  ;  one  bone  cor- 
responding to  that  of  the  thumb  and  two  fingers ;  that  next  to 
the  thumb  consisting  of  two  phalanges,  and  the  outer  one,  of  a 
single  bone. 

1007.  In  the  legs  we  find  a  femur  and  a  tibia,  to  which  there 
adheres  a  very  slender  fibula,  (which  is,  indeed,  often  wanting ;) 
one  metatarsal  bone,  and  the  phalanges  of  the  toes.  The  patella 
is  often  supplied  by  a  process  from  the  tibia. 

1008.  The  muscles  possess  a  high  degree  of  irritability,  and 
contract  with  great  quickness  and  force.  Many  of  the  tendons 
become  ossified  in  the  progress  of  age.     A  remarkable  arrange- 


BIRDS.  401 

ment  exists  in  the  tendons  of  the  flexor  muscles  of  the  toes,  by 
which  the  flexion  of  the  knee  and  heel  puts  them  on  the  stretch, 
and  thus  mechanically  bending  the  toes,  enables  the  bird  to  lay 
firm  hold  ol"  the  branch  of  a  tree  or  perch  whilst  roosting.  This 
is  effected  by  the  flexor  tendons  passmg  round  over  the  outer 
side  of  the  angle  formed  by  each  of  these  joints.  Thus  a  bird, 
while  roosting,  supports  itself  on  one  leg  only,  by  the  mere  eftect 
of  the  weight  of  the  body  producing  the  necessary  flexion  of  the 
toes,  to  enable  it  to  preserve  its  hold.  This  remarkable  provision 
of  nature  was  long  ago  observed,  and  well  explained  by  Borelli ; 
and  though  the  fact  has  been  controverted  by  Vicq.  D'Azyr,  it 
appears  to  be  well  established.  In  order  to  give  great  latitude 
of  motion  to  the  head,  the  articulation  of  the  os  occipitis  with 
the  atlas  is  performed  by  a  single  condyle  only,  which  procures 
it  the  advantages  of  a  ball  and  socket  jonit.  This  condyle  is 
situated  at  the  anterior  margin  of  the  great  occipital  foramen. 
The  proper  bones  of  the  cranium  are  not  joined  by  sutures,  but 
are  consolidated  into  a  single  piece.  The  orbits  for  the  eyes  are 
very  large,  and  are  frequently  found  to  communicate  laterally  in 
the  skeleton,  being  separated,  in  the  living  animal,  only  by  a  thin 
membranous  partition.  The  ossa  unguis  are  generally  very  large. 
The  upper  jaw  is  almost  always  moveable  upon  the  other  bones 
of  the  head.  To  this  bone  is  joined  the  bill,  the  structure  of  which 
is  horney,  and  thus  supplies  the  place  of  teeth,  occupying 
the  situation  of  the  palate.  The  functions  of  the  teeth,  indeed, 
are  not  wanted,  for  the  animal  swallows  its  food  without  any 
mastication.  The  lower  jaw  is  connected  with  the  skull  by  the 
intermedium  of  a  peculiar  bone  of  irregular  form,  called  the  os 
quadratum.  Another  small  bone  resting  against  the  palate  is 
connected  with  it. 

J  009.  The  energy  of  the  digestive  functions  in  birds  corres- 
ponds with  that  of  respiration,  and  muscular  irritability.  The 
stomach  may  be  considered  as  consisting  of  three  cavities ;  the 
first  of  which,  termed  the  crop,  is  rather  a  dilatation  of  the 
oesophagus,  furnished  with  numerous  glands  disposed  in  a  regular 
arrangement  of  rows  ;  the  second  is  the  ventriculus  succenturia- 
tus,  or  pro-ventricuhs,  situated  lower  down,  and  just  at  the  en- 
trance of  the  proper  stomach.  It  is  furnished  with  a  still  more 
complex  glandular  apparatus ;  and  hence  has  been  termed  the 
hulhus  glandulosus.  Its  form  and  structure  vary  much  in  differ- 
ent genera  of  birds.  The  third  is  the  proper  stomach,  which 
resembles  in  the  structure  of  its  coats  the  simple  stomachs  of  the 
mammalia,  being  thin  and  membranous  in  those  birds  which  feed 
on  insects  and  flesh.  But  in  all  granivorous  birds  the  coats  of 
this  stomach  are  farther  armed  with  a  thick  cuticular  lining,  of 
nearly  the  density  of  horn,  which  is  surrounded  by  four  immensely 
thick  and  powerful  muscles,  capable  of  exerting  a  strong  com- 

34* 


402  COMPARATIVE    PHYSIOLOGY. 

pression  on  the  contents  of  the  stomach,  and  a  slight  degree  of 
lateral  motion,  and  thus  performing  the  office  of  trituration. 
Such  is  the  structure  of  what  is  called  a  gizzard.  Between  these 
opposite  structures  there  exists,  in  different  species  of  birds,  a 
great  number  of  intermediate  gradations,  corresponding  to  the 
peculiar  nature  of  the  food  to  which  nature  has  adapted  their 
organization.  The  trituration  of  the  grain  is  assisted  by  small 
stones  voluntarily  swallowed  by  the  animal,  and  in  the  selection 
of  which  the  animal  is  directed  by  a  principle  of  instinct. 

1010.  The  intestinal  canal  of  birds  is  much  shorter  than  in 
most  of  the  mammalia  ;  but  a  similar  disparity  is  also  noticed  in 
the  former,  with  regard  to  the  greater  length  of  the  canal  in  birds 
consuming  vegetable  food,  when  compared  with  that  of  the 
carnivorous  tribes.  There  is  scarcely  any  distinction  in  point  of 
size  between  the  small  and  large  intestines ;  though  the  division 
between  them  is  generally  marked  by  the  presence  of  two  coeca. 
The  rectum  terminates  in  an  expansion,  termed  the  cloaca,  in 
which  the  ureter  terminates,  and  which  therefore  performs  the 
function  of  the  urinary  bladder.  Connected  with  the  cloaca, 
there  is  an  oval  glandular  bag  termed  the  bursa  Fahricii,  and 
opening  into  it  by  a  narrow  longitudinal  aperture.  The  oviduct 
in  the  female  also  opens  into  the  same  cavity.  Two  bhnd  pouches, 
opening  into  the  rectum,  are  found  near  to  its  termination. 

1011.  The  liver  of  birds  is  usually  divided  into  two  lobes;  but 
in  some  birds  there  is  in  addition  a  third  smaller  lobe.  Two 
ducts  proceed  from  the  liver;  the  one  is  the  hepato-cystic  duct, 
the  other  the  hepatic  duct.  The  former  conveys  the  bile  into 
the  gall  bladder,  the  latter  into  the  duodenum.  'Thus  the  bile  is 
conducted  into  the  duodenum  by  one  hepatic  duct  distinct  from 
the  cystic  duct,  and  these  two  alternately  with  two  or  three 
ducts  from  the  pancreas,  which  is  large,  and  generally  consists 
of  two  distinct  glands  ;  the  spleen,  on  the  other  hand,  is  usually 
round,  and  of  small  size.  The  gall-bladder  is  situate  under  the 
right  lobe  of  the  liver  ;  but  some  birds  have  no  gall-bladder. 
There  is  no  omentum.  The  chyle  is  transparent;  there  are  no 
glands  in  the  mesentery  ;  the  thoracic  duct  is  double.  Magendie 
has  denied  the  existence  of  lymphatic  vessels  in  birds  ;  but  they 
have  been  distinctly  seen  by  others.  The  kidneys  form  a  double 
row  of  conglobate  glands,  connected  together,  and  situate  on  the 
sides  of  the  lumbar  vertebrae,  in  the  hollows  of  the  ossa  innominata. 
There  is  no  cavity  corresponding  to  the  pelvis  of  the  kidneys  of 
the  mammalia  ;  but  renal  capsules,  similar  to  those  of  mammalia, 
are  found  also  in  birds. 

1012.  The  heart  of  birds  is  furnished,  as  in  the  mammalia,  with 
a  double  set  of  cavities ;  the  one  subservient  to  the  general  or 
systemic,  and  the  other  to  the  pulmonary  circulation.  The  valves 
of  the  right  ventricle  are  supplied  by  a  strong  triangular  muscle. 


BIRDS.  403 

which  gives  additional  impetus  to  the  blood  propelled  into  the 
pulmonary  artery.  Jacobson  has  discovered  a  singular  distribu- 
tion in  the  abdominal  veins ;  those  returning  the  blood  from  the 
hinder  extremities  being  ramified  through  the  kidneys  and  Uver, 
previously  to  their  termination  in  the  vena  cava. 

1013.  The  lungs  are  not  divided  into  lobes,  and  are  fixed  in 
their  situation,  being  tightly  braced  in  the  cavity  formed  by  the 
ribs,  on-each  side,  by  a  membrane,  which  is  perforated  by  a 
number  of  holes.     These  apertures  are  the  terminations  of  col- 
lateral branches  of  the  bronchia,  through  which  the  air  received 
into  the  chest  passes  out,  and  circulates  through  a  multitude  of 
cells  interspersed  through  various  parts  of  the  body,  and  com- 
municating ultimately  with  the  central  cavities  of  the  bones.     An 
immense  surface  is  thus  exposed  to  the  influence  of  the  air,  which, 
having  access  to  every  part  of  the  body,  acts  very  extensively 
on  the  blood  circulating  in  the  vessels  lining  these  air-cells  and 
cavities.     Hence  the  energy  of  the  function  of  respiration  is 
greater,  and  the  temperature  higher,  than  in  any  of  the  mam- 
malia.    There  is  properly  no  diaphragm  in  birds ;  a  few  muscular 
fibres  only  surround  the  larger  air-cells,  and  assist  in  expelling 
the  air  from  them  back  again  into  the  lungs.     The  trachea  is 
supported  by  a  series  of  cartilages,  which  form  entire  rings,  and 
overlap  each  other  at  their  upper  and  lower  margins,  so  as  to 
preserve  the  tube  open  amidst  the  violent  bendings  and  twistings 
of  the  neck.     It  is  provided,  at  its  bifurcation,  with  a  peculiar 
set  of  muscles,  which,  aided  by  a  second  rima  glottidis,  enable 
this  part  to  perform  the  functions  of  a  second  larynx,  and  to  give 
rise  to  sounds;  and,  indeed,  to  be  apparently  the  principal  organ 
of  the  voice.     In  many  aquatic  birds,  as  in  the  male  swan,  the 
trachea  makes  a  large  circumvolution,  which  is  contained  in 
the  hollow  of  the  sternum.     In  other  birds  it  is  not  enclosed  in 
this  bone  ;  but  there  is  a  bony  structure  surrounding  the  inferior 
larynx,  which  tends  to  strengthen  the  voice.     These  convolutions 
and  bony  cells  of  the  trachea,  have  been  compared  in  their  ofUce 
to  the  turns  of  the  French-horn,  or  the  divisions  of  a  basoon. 
This  great  development  of  the  vocal  organs  is  peculiar  to  the 
male  bird. 

1014.  The  brain  of  birds  is  characterized  by  the  smallness  of 
the  hemispheres,  which  are  not  united  by  any  corpus  callosum. 
There  is  no  appearance  of  convolutions  on  its  surface.  The 
optic  thalami  are  voluminous,  and  are  situate  behind  and  below 
the  hemispheres  ;  a  cavity  is  found  in  each.  The  crura  of  the 
cerebellum  do  not  form  any  eminence  at  their  junction  with  the 
medulla  oblongata,  corresponding  to  the  pons  varolii.  The 
cerebellum  is  comparatively  large,  but  has  no  lateral  lobes,  being 
almost  wholly  constituted   by  the  processus  vermiformis.     The 


404  COMPARATIVE    PHYSIOLOGY. 

total  bulk  of  the  brain,  compared  with  the  size  or  weight  of  the 
body,  is  generally  greater  than  in  the  mammalia. 

1015.  The  eyes  of  birds  are  very  large,  in  proportion  to  the  size 
of  the  head,  and  appear  to  be  adapted  to  a  great  range  of  vision. 
The  adjustment  of  the  position  of  the  lens  appears  to  be  effected 
by  means  of  a  vascular  and  plicated  membrane,  called  the  mar- 
swpium,  extending  obliquely  from  the  bottom  of  the  retina,  through 
the  vitreous  humor,  to  the  edge  of  the  crystalline.  Its  figure  is 
trapezoidal ;  its  surface  is  covered  with  the  pigmentum  nigrum, 
which  of  course  absorbs  all  the  rays  of  fight  that  fall  upon  it. 
The  anterior  part  of  the  eye-ball  is,  in  many  carnivorous  birds, 
strengthened  by  a  circle  of  bony  plates,  lying  close  upon  the 
sclerotica,  and  overlapping  each  other.  Besides  the  two  external 
eye-lids,  birds  are  always  provided  with  a  strong  nictitating 
membrane,  proceeding  from  the  internal  corner  of  the  eye,  and 
drawn  over  the  cornea  by  a  special  muscular  apparatus.  In 
some  birds  the  lower  eye-lid  is  the  most  moveable,  and  in  others 
it  is  the  upper. 

1016.  There  is  no  cartilaginous  external  air;  what  has  this 
appearance  in  the  owl  is  formed  only  by  the  feathers ;  the  cavity 
of  the  tympanum  contains  only  one  ossiculum  auditus.  and  com- 
municates with  the  air-cells  of  the  skull.  The  Eustachian  tubes 
have  a  common  opening  over  the  arch  of  the  palate.  The  part 
corresponding  to  the  cochlea  has  the  figure  of  a  cone,  with 
scarcely  any  curvature,  but  with  two  scalse.  The  semicircular 
canals  are  large,  and  project  from  the  bone. 

1017.  The  nasal  organs  are  unprovided  with  an  aithmoid 
bone ;  the  olfactory  nerves,  passing  to  them  through  the  orbits, 
and  being  distributed  upon  the  hullcB  turbinatcB,  which  are  oftener 
cartilaginous  than  osseous  in  their  structure. 

1018.  The  tongue  is  thick  and  fleshy,  covered  with  a  thick 
cuticle,  and  therefore  not  adapted  to  be  an  organ  of  taste.  It  is 
supported  by  an  os  hyoides  of  a  singular  shape,  having  besides 
the  anterior  and  posterior  processes,  and  the  cornua,  with  their 
appendices,  another  bone  jointed  to  it  anteriorly,  and  moveable 
on  it.  This  last  bone,  which  supports  the  tongue,  is  called  the 
lingual  bone. 

1019.  The  evolution  of  the  chick  from  the  egg  being  a  subject 
of  great  interest,  has  long  engaged  the  attention  of  physiologists. 
The  following  is  an  outline  of  the  history  of  these  changes  in  the 
common  fowl.  The  ovulum,  or  first  rudiment  of  the  Qg,g,  is 
formed  in  the  ovary,  and  consists  simply  of  a  bag  containing  the 
yolk;  this  afterwards  becomes  covered  in  its  progress  along  the 
oviduct,  by  successive  layers  of  albuminous  substance,  which 
composes  the  white  of  the  egg,  so  called  from  the  colour  it  as- 
sumes when  coagulated.  The  white  of  the  egg  is  invested  with 
a  firm  membrane,  which  is  easily  divisible  into  two  layers;  and 


BIRDS.  405 

there  are  also  other  membranes  dividing  the  mass  of  albumen 
into  concentric  layers.  The  membrane  of  the  yolk,  the  mem- 
hrana  vitelli,  or  yolk-hag,  is  connected  with  that  of  the  white,  or 
the  memhrana  alhuminis,  by  a  kind  of  ligament,  which  extends 
from  the  two  ends  or  sides  of  the  yolk,  to  those  of  the  white ; 
these,  when  partially  stretched  and  torn  by  the  motion  of  the 
yolk,  have  a  flocculent  appearance,  and  form  what  are  called  the 
chalazcB.  They  appear  to  act  as  ligaments  to  the  yolk,  keeping 
that  surface  uppermost  in  which  the  chick  is  situated,  so  that  it 
may  receive  warmth  from  the  hen  during  incubation.  In  the 
lower  part  of  the  oviduct  the  egg  acquires  a  calcareous  covering 
or  shell,  which  is  secreted  by  the  inner  membrane  of  that  canal, 
and  which  is  composed  of  nine-tenths  carbonate  of  lime,  the 
remaining  portion  being  phosphate  of  lime  and  animal  matter. 
Between  the  two  membranes  which  line  the  shell,  a  small  quan- 
tity of  air  is  contained  at  the  larger  end  of  the  egg. 

1020.  A  small,  round,  milk-white  spot,  called  the  cicatricula, 
is  formed  on  the  surface  of  the  yolk-bag  during  incubation.  It  is 
surrounded  by  two  or  three  concentric  circles,  called  the  halones. 
Previously  to  the  appearance  of  the  embryo,  a  small  shining  spot 
of  an  elongated  form,  with  rounded  ends,  but  contracted  in  the 
middle,  is  seen  within  the  cicatricula.  This  is  called  the  areola 
pellucida.  In  the  centre  of  this  may  be  discerned,  on  the  second 
day,  a  gelatinous  filament,  bent  into  a  curve.  This  is  the  primitive 
trace,  or  earliest  perceptible  rudiment  of  the  chick,  in  which  the 
first  organs  that  can  be  discovered  are  the  two  lobes  of  the  brain, 
and  the  primitive  filaments  of  the  spinal  cord,  with  caudal 
dilatation.  Vessels  begin  to  appear  on  the  surface  of  the  yolk-bag, 
being  spread  on  a  separate  membrane,  and  presenting  what  has 
been  called  the  figura  venosa,  or  area  vasculosa,  the  marginal 
vessel  at  the  remotest  part  being  termed  the  vena  terminalis. 
These  veins  correspond  to  the  mesenteric  veins ;  they  are  collected 
together,  and  form  the  vena  portse,  whilst  the  arteries  are  derived 
from  the  mesenteric  artery  of  the  chick.  The  heart  may  next 
be  perceived,  as  three  red  pulsating  points,  constituting  the punctum 
saliens.  These  points  are  the  rudiments  of  the  auricle,  ventricle, 
and  aorta.  Next,  the  separate  vertebras  may  be  distinguished, 
then  the  eyes,  and  afterwards  the  stomach,  fiver,  and  intestines. 
Then  a  vascular  membrane,  the  allontois,  is  rapidly  formed,  having 
the  form  of  a  bladder  communicating  with  the  cloaca.  It  soon 
extends  over  nearly  the  whole  of  the  internal  membrane  of  the 
shell,  and  is  covered  with  num.erous  ramifications  of  arterial  and 
venous  vessels,  derived  from  the  internal  iliacs  of  the  chick  ;  the 
former  contain  carbonized  blood,  and  are  therefore  dark  coloured; 
the  latter,  which  conduct  back  the  same  blood  after  it  has  received 
the  influence  of  the  air  at  the  surface,  have  a  bright  scarlet  hue, 
and  unite  in  forming  the  umbilical  vein  of  the  chick.     Hence  it  is 


406  COMPARATIVE    PHYSIOLOGY. 

evident  that  this  membrane  performs  a  function  analogous  to  that 
of  the  placenta  in  mammalia,  and  to  that  of  the  future  air-cells  of 
the  lungs,  or,  in  other  words,  that  it  is  the  organ  of  embryonic 
respiration.  The  chick  is  nourished  by  the  matter  of  the  yolk, 
which  is  partly  absorbed  by  yellow  vessels  {vasa  vitelli  lutea) 
having  a  fringed  appearance,  and  flocculent  extremities,  floating 
in  the  yolk,  and  partly  by  the  direct  passage  of  this  matter  into 
the  intestine  by  means  of  a  canal  of  communication,  called  the 
ductus  vitello-intestinalis.  The  white  of  the  egg  also  gradually 
disappears,  being  absorbed  into,  and  mixed  with  the  yolk.  Towards 
the  latter  periods  of  incubation,  the  whole  of  the  yolk-bag  is  taken 
into  the  abdomen,  and  soon  disappears.  On  the  twenty-first 
day  of  incubation,  the  chick,  being  fully  formed,  breaks  the  shell 
which  confines  it,  and  enters  into  the  world  ;  for  which  temporary 
purpose  it  is  provided  with  a  hard  beak,  which  is  afterwards  lost. 

2.  Peculiarities  in  particular  Families  and  Genera  of  Birds. 

1021.  The  shades  of  difference  in  the  anatomy  of  each  organ 
in  individual  genera  and  species  of  birds,  are  exceedingly  numerous, 
and  to  enter  into  their  detail  would  far  exceed  the  limits  within 
which  we  are  obliged  to  confine  ourselves  in  this  treatise.  We 
must  not,  however,  pass  over  some  of  the  most  remarkable 
differences  which  offer  themselves  to  our  notice  in  a  few  families 
of  birds.  Amongst  these  none  are  more  singular  than  those 
presented  by  the  tribe  of  the  brevipennes  of  Cuvier,  comprehending 
the  ostrich  and  the  cassowary.  These  birds  not  being  intended 
for  flight,  have  very  imperfectly  formed  wings ;  the  sternum 
exhibits  no  carinated  figure,  but  presents  a  plane  and  uniform 
surface,  being  destitute  of  an  inferior  spine ;  the  pectoral  muscles 
of  the  hinder  extremity,  on  the  contrary,  are  very  large  and 
powerful.  The  furcular  bone  exists  only  in  a  rudimental  state. 
The  pelvis  of  the  ostrich  differs  from  that  of  all  other  birds  in 
being  closed  below  by  the  complete  junction  of  the  ossa  pubis. 
The  coeca  in  this  bird  are  furnished  with  a  remarkable  spiral 
valve.  The  feathers  are  also  exceedingly  peculiar ;  but  as  this 
subject  belongs  rather  to  the  external  characters,  we  cannot  dwell 
upon  it  here. 

1022.  The  same  consideration  prevents  us  from  dilating  on 
the  varieties  in  the  structure  of  the  bill,  and  of  the  toes,  which 
offer  to  the  naturalist  abundant  topics  of  interesting  inquiry.  We 
shall  only  remark  that  the  cellular  bills,  which  are  of  such  enor- 
mous size  in  the  levirostres,  have  free  communications  with  the 
air  cells  subservient  to  respiration,  and  may  therefore  be  auxiliary 
to  that  function. 

1023.  The  tongue  of  the  woodpecker  is  provided  with  a  sin- 
gular apparatus  for  darting  it  forwards  with  great  rapidity ;  this 


REPTILES.  407 


is  effected  by  a  long  cartilaginous  band,  which  passes  completely 
over  the  top  of  the  craniunn,  and  is  fixed  to  a  groove  on  the  right 
side  of  the  upper  jaw. 


Sect.  III. — Comparative  Physiology  of  Reptiles. 

1.  Reptiles  in  General. 

1024.  The  class  of  reptiles  comprehends  all  those  vertebrated 
animals  which  breathe  atmospheric  air  by  means  of  lungs,  but 
which  are  cold-blooded.     This  latter  quality  is  a  consequence  of 
the  partial  extent  of  their  respiration,  the  heart  being  so  con- 
structed as  to  transmit  to  the  lungs  only  a  portion  of  the  circu- 
lating blood,  and  the  remaining  part  being  again  sent  into  the 
arterial  system  of  the  body  without  having  been  exposed  to  the 
,.action  of  the  air.     Reptiles  are  distinguished  by  the  negative 
characters  of  being  destitute  of  either  hair  or  feathers,  and  having' 
no  mammffi,  organs  for  which  there  appears  to  be  no  occasion, 
in  consequence  of  these  animals  being  oviparous.     The  limited 
degree  in  w^hich  their  blood  is  oxygenated  appears  to  have  a 
considerable  influence  on  the  whole  condition  of  their  vital  func- 
tions.   Not  only  is  the  temperature  of  the  blood  scarcely  different 
from  that  of  the  surrounding  medium,*  the  actions  of  life  seem 
to  be  more  sluggish  and  torpid,  and  the  muscular  powers  less 
energetic ;  their  sensations  are  more  obtuse,  and  in  cold  climates 
they  pass  the  winter  in  a  state  of  torpor.     The  comparative 
smallness  of  the  pulmonary  system  of  vessels,  and  the  less  extent 
of  the  surfaces  of  the  air-cells  of  the  lungs,  render  them  less 
dependent   on   respiration  than  warm-blooded  animals;    hence 
they  bear  submersion  under  water  for  a  considerable  time  with 
impunity,  although,  if  the  interruption  to  respiration  be  too  long 
continued,  they  ultimately  perish,  with  as  much  certainty  as  any 
of  the  mammalia  would  do  under  similar  circumstances. 

There  is  ground  for  believing,  according  to  Geofiroi  St.  Hilaire, 
that  crocodiles  and  turtles  possess,  in  addition  to  the  ordinary 
pulmonary  respiration,  a  partial  aquatic  abdominal  respiration, 
effected  by  means  of  two  channels  of  communication  which  have 
been  found  to  exist  between  the  cavity  of  the  abdomen  and  the 
external  surface  of  the  body,  and  also  that  some  analogy  may  be 
traced  between  this  aquatic  respiration  in  reptiles,  by  these  ^jen- 
toneal  canals,  and  the  supposed  function  of  the  swimming  bladder 
of  fishes,  hereafter  to  be  described,  in  subserviency  to  a  species 
of  aerial  respiration. 

*  The  temperature  of  animals  of  this  class  has  been  shown  by  the  experi- 
ments of  Dr.  Davy,  Tiedemann,  Czermack,  and  Wilford,  to  be  in  general 
two  or  three  degrees  higher  than  that  of  the  surrounding  medium.  It  par- 
takes, however,  of  the  vicissitudes  of  temperature  in  that  medium. 


408  COMPARATIVE    PHYSIOLOGY. 

1025.  As  their  vital  functions  do  not  require  for  their  perform- 
ance any  elevated  temperature,  so  we  find  reptiles  destitute  of 
those  appendages  to  the  integuments,,  such  as  hair,  wool,  or 
feathers,  which  in  the  other  classes  retain  the  warmth  of  the  body. 
Their  brain  is  very  small,  compared  with  the  rest  of  the  nervous 
system,  being  less  necessary  for  the  exercise  of  the  vital  actions. 
The  parts  immediately  instrumental  in  sensation  are  less  con- 
centrated in  a  particular  spot,  but  would  appear  to  be  more 
diffused  over  the  spinal  cord  and  ganglia.  Thus  they  not  only 
continue  to  live,  but  even  exhibit  motions  which  have  the  sem- 
blance of  being  voluntary,  though  probably  not  so  in  reality,  long 
after  the  loss  of  the  brain,  or  even  of  the  entire  head.  In  like 
manner  the  irritability  of  their  muscles  is  retained  for  a  much 
longer  time,  after  they  have  been  separated  from  the  body,  than 
in  the  case  of  warm-blooded  animals.  The  heart,  when  removed 
from  the  body,  still  continues  to  beat  for  several  hours ;  and  the 
body,  thus  deprived  of  its  heart,  may  still  possess  the  power  of 
voluntary  motion,  in  consequence  of  the  continuance  of  a  species 
of  obscure  circulation,  which  is  carried  on  in  the  capillary  system 
of  vessels. 

1026.  Reptiles  present  a  much  greater  variety  of  forms  and  of 
structures  than  is  met  with  in  any  other  class  of  vertebrata.  The 
characters  of  the  orders  are  derived  principally  from  the  form 
of  their  organs  of  progressive  motion.  These  orders  are  four  in 
number,  namely,  chelonia,  sauria,  ophidia,  and  batrachia. 

2.  Chelonia. 

1027.  This  order  comprehends  turtles  and  tortoises,  animals 
whose  skeleton  presents  a  trunk  composed  of  two  large  plates  of 
bone,  the  one  derived  from  an  expansion  of  the  dorsal  vertebra 
and  ribs,  the  other  from  a  corresponding  expansion  of  the  sternum ; 
these  are  united  at  the  edges,  and  form  a  complete  case  for  the 
thoracic  and  abdominal  viscera,  leaving  apertures  in  front  for 
the  head  and  neck,  together  with  the  fore  legs,  and  behind  for 
the  hind  legs  and  tail.  This  arrangement  produces  a  singular 
reversal  of  the  positions  of  the  scapula,  the  pelvis,  and  the  muscles 
attached  to  these  bones,  all  of  which,  instead  of  being  placed 
externally,  are  situated  in  the  interior  of  the  ribs.  The  humerus 
is  remarkably  curved,  especially  in  the  tortoise,  where  it  has 
nearly  the  form  of  a  semicircle.  The  radius  and  ulna  are  distinct 
from  each  other  ;  the  carpus  and  phalanges  are  short  and  stunted, 
forming  a  compressed  sort  of  hand.  The  vertebrse  of  the  neck 
and  tail  are  the  only  parts  of  the  spinal  column  which  are  move- 
able upon  one  another. 

1028.  The  cavity  in  which  the  brain  is  contained  is  very 
small  compared  with  the  size  of  the  skull,  the  greater  part  of 


REPTILES.  409 

which  consists  of  the  bones  surrounding  the  orbit,  and  giving 
attachment  to  the  large  muscles  that  move  the  jaw.  There  are 
no  teeth,  and  the  horny  coverings  of  the  jaws  has  some  resem- 
blance to  a  horse's  hoof  in  the  mode  of  its  connexions  with  the 
bones.  The  tongue  is  short,  and  covered  with  villi,  which  extend 
also  down  the  ossophagus ;  their  points  are  all  directed  towards 
the  stomach,  so  as  to  prevent  the  return  of  the  food  when  it  is 
once  swallowed.  The  stomach  is  simple  in  its  structure ;  the 
intestinal  canal  of  moderate  length ;  its  inner  membrane  presenting 
only  longitudinal  folds,  together  with  innumerable  villi,  which 
are  more  thickly  set  in  the  upper  part  of  the  canal  than  in  the 
lower;  there  is  no  coecum,  but  occasionally  small  processes,  or 
appendices  epiploicas,  are  attached  to  the  outer  membrane.  The 
urinary  bladder  is  exceedingly  capacious.  The  lungs  are  volu- 
minous, and  are  contained  in  the  same  cavity  as  the  abdominal 
viscera.  The  air-cells  are  very  large,  and  the  general  texture  of 
the  lungs  is  loose.  Respiration  is  performed  entirely  by  the 
muscles  of  deglutition  ;  the  animal  in  fact  closes  its  mouth,  and 
swallows  the  air  received  from  the  nostrils,  which  is  thus  poured 
down  into  the  trachea,  the  os  hyoides  being  alternately  raised 
and  depressed.  The  liver  is  divided  into  two  round  irregularly- 
shaped  masses. 

1029.  The  heart  has  two  auricles,  separated  by  a  complete 
septum,  the  one  receiving  the  blood  from  the  venas  cavEe,  the 
other  from  the  pulmonary  veins.  The  ventricle  into  which  these 
veins  pour  their  contents  is  single,  but  has  two  chambers  of 
unequal  size,  which  communicate  together,  so  that  the  blood 
received  from  the  lungs  is  more  or  less  mixed  Math  that  returning 
from  the  body  in  the  systemic  circulation ;  and  it  is  this  mixed 
blood  which  is  sent  through  the  aorta.  The  pulmonary  artery 
is  merely  a  branch  of  the  aortic  system. 

1030.  In  the  internal  ear,  we  find  a  tympanum,  Eustachian 
tube,  and  semicircular  canals,  together  with  ossicular,  and  also 
stony  concretions  in  the  vestibule.  The  eye  has  a  bony  ring  at 
the  anterior  part  of  the  sclerotica,  as  in  birds.  There  are  large 
lacrymal  glands,  and  a  very  moveable  membrana  nictitans. 

3.  Sauria. 

1031.  The  various  animals  included  in  this  order,  or  the  tribe 
of  lizards,  have  a  heart  with  two  auricles,  with  generally  four 
feet,  and  a  scaly  integument.  They  are  always  provided  with 
teeth,  and  with  nails;  there  is  invariably  a  tail.  The  ribs  are 
very  moveable,  and  their  motions  are  subservient  to  respiration. 
The  lungs  are  long  and  vesicular,  extending  far  into  the  abdominal 
cavity. 

35 


410  COMPARATIVE    PHYSIOLOGY. 

1032.  The  crocodile  may  be  taken  as  an  example  of  this  order- 
Its  jaws  are  of  immense  size.  The  upper  jaw  consists  of  a  large 
intermaxillary  bone,  which  is  immoveably  joined  with  the  skull, 
although  the  animal,  in  opening  the  mouth,  appears  to  raise  it 
independently,  a  circumstance  which  misled  the  older  naturalists 
into  the  belief,  that  it  was  really  moveable.  There  is  an  os  quad- 
ratum  as  in  birds.  The  sternum  extends  to  the  abdomen,  and 
consists  of  seven  pair  of  cartilaginous  arches,  to  which  ten  ribs, 
not  however  reaching  to  the  spine,  are  attached.  There  are  no 
clavicles.  The  tongue  is  thick  and  flat,  and  attached  very  near 
its  edges  to  the  jaws,  so  as  not  to  be  easily  perceived. 

The  teeth  are  of  the  simple  conical  kind,  chiefly  adapted  to  the 
prehension  and  retention  of  the  food ;  and  each  tooth  when  worn 
is  replaced  by  a  fresh  one,  which  grows  underneath  it ;  a  suc- 
cession which  takes  place  several  tir|ies  during  the  hfe  of  the 
animal. 

The  oesophagus  has  the  shape  of  a  funnel,  and  leads  to  a  stomach 
which  resembles  that  of  granivorous  birds,  in  the  thickness  of  its 
coats,  and  the  approximation  of  its  two  apertures.  The  liver  has 
two  distinct  lobes.  There  is  no  urinary  bladder.  The  single 
ventricle  of  the  heart  is  divided  into  three  compartments,  which 
communicate  together ;  there  is  one  cavity  belonging  to  each 
auricle,  and  an  intermediate  cavity,  into  which  the  blood  from  the 
two  others  is  poured,  and  where  the  intermixture  of  the  carbonized 
and  oxygenated  portions  is  made.  There  is  an  external  meatus 
of  the  ear,  which  may  be  voluntarily  closed  by  a  species  of  lips. 
Ossicula  auditus  are  found,  as  well  as  stony  concretions  in  the 
vestibule.  In  the  other  kinds  of  lizards,  the  tympanum  is  on  a 
level  with  the  integuments,  and  there  is  no  external  meatus.  A 
membrana  nictitans  is  found  in  the  eye.  The  area  of  the  section 
-  of  the  cavity  containing  the  brain  does  not  occupy  the  one- 
twentieth  part  of  that  of  the  whole  head. 

1033.  The  chameleon  has  comparatively  a  large  head  ;  but 
its  brain  is  only  of  the  size  of  a  pea.  Its  lungs  have  numerous 
projecting  processes.  The  tongue  is  constructed  in  a  manner 
which  bears  some  analogy  to  that  of  the  woodpecker  in  the 
mechanism  by  which  it  is  darted  forwards  to  a  considerable 
distance  from  the  head,  and  suddenly  retracted.  It  terminates 
in  a  sort  of  club,  which  is  moistened  with  a  glutinous  secretion, 
for  seizing  flies  and  other  insects,  and  its  upper  surface  is  hol- 
lowed. The  eyes  project  considerably  from  the  head,  and  admit 
of  being  turned  very  freely  in  their  orbits.  The  most  singular 
circumstance  in  the  constitution  of  this  animal,  is  the  change  of 
colour  of  its  skin  under  various  circumstances  of  temperature  or 
excitement.  These  changes  appear  to  be  connected  with  the 
variable    activity  of  respiration,  which  quickly  influences   the 


REPTILES.  411 

colour  of  the  blood  circulating  under  the  very  transparent  skin ; 
and  which  is  visible  to  a  greater  depth,  in  consequence  of  the 
ample  extension  of  the  lungs  along  the  sides  of  the  abdomen  : 
when  the  lungs  are  inflated,  indeed,  the  whole  body  appears  as 
if  it  were  semi-transparent. 

1034.  The  draco  volans  is  a  remarkable  instance,  in  this  tribe, 
of  the  subserviency  of  the  ribs,  which  are  expanded  on  each  side 
so  as  to  support  a  thin  membrane  resembling  a  wing,  to  the  pur- 
poses of  progressive  motion. 

4.  Ophidia. 

1035.  Serpents,  being  wholly  without  feet,  are  constrained  to 
crawl  upon  the  surface  of  the  earth,  and  are,  therefore,  more 
especially  entitled  to  the  appellation  of  reptiles. 

1036. 'Their  skeleton  presents  us  with  the  simplest  possible 
condition  of  the  vertebral  type  ;  for  it  consists  merely  of  a  simple 
spinal  column  descending  from  the  head,  and  furnished  only  with 
ribs.  There  appears,  at  first  sight,  to  be  no  vestige  either  of 
sternum,  of  scapula,  or  of  pelvis;  the  body  of  each  vertebra  is 
articulated  by  a  convex  surface,  which  is  received  into  a  concave 
surface  of  the  next.  The  number  of  vertebras  is  often  exceed- 
ingly great ;  being  sometimes  as  many  as  three  hundred.  The 
number  of  the  ribs  coi responds  with  that  of  the  vertebrse,  and 
when  acted  upon  by  their  muscles,  they  assist  in  the  progressive 
motion  of  the  animal,  by  pressing  on  the  gi'ound,  in  succession, 
like  imperfect  feet.  In  the  rattle-snake,  the  last  vertebrae  of  the 
tail  are  broad  and  covered  with  the  hollow  pieces  which  com- 
pose the  rattle.  Obscure  rudiments  of  pelvic  bones  were  found 
by  Mayer  to  exist  in  the  anguis  fragilis,  the  anguis  ventralis,  and 
the  typhlops  crocotatus ;  and  it  is  probable  that  they  may  be 
discovered  in  most  reptiles  of  this  order.  Some  serpents  have 
external  claws,  which  may  be  considered  as  rudiments  of  feet. 
In  others  they  exist  concealed  under  the  skin ;  and  in  others, 
again,  there  are  cartilaginous  filaraents'which  Mayer  regards  as 
rudimental  claws,  connected  with  a  series  of  small  bones,  which 
appear  to  be  the  rudiments  of  the  hones  of  the  lower  extremities. 

1037.  The  upper  jaw-bone  is  detached  from  the  rest  of  the 
skull,  and  admits  of  great  latitude  of  motion.  In  most  species 
of  serpents,  the  jaws  are  so  constructed  as  to  render  the  mouth 
capable  of  great  dilatation,  and  to  enable  it  to  receive  objects 
even  larger  than  the  animal  itself,  and  a  corresponding  power  of 
dilatation  exists  also  in  the  oesophagus. 

1038.  Serpents  that  are  not  venomous  have  usually  four  max- 
illary bones  in  the  upper  jaw,  beset  with  small  teeth,  placed  in 
two  rows,  widely  separated  from  one  another.  The  external 
row  is  not  found  in  venomous  serpents,  but  in  their  place  large 


412  COMPARATIVE    PHYSIOLOGY. 

tubular  fangs  are  met  with,  which  are  the  terminations  of  the 
ducts  from  the  poison  bags,  and  which  convey  the  venom  into 
the  wound  inflicted  by  the  tooth.  This  poison  is  secreted  by 
glands,  situated  below  the  eyes,  and  surrounded  by  very  strong 
muscles. 

1039.  The  stomach  of  serpents  can  scarcely  be  distinguished 
from  the  lower  extremity  of  the  oesophagus,  and  is  very  short, 
compared  with  the  great  length  of  that  canal.  There  is  no  uri- 
nary bladder,  the  ureters  opening  at  once  into  the  cloaca. 

1040.  The  heart  has  generally  two  auricles,  though  in  some 
genera  only  one  is  met  with;  the  ventricle  is  always  single.  The 
lungs  consist  of  a  membranous  cavity,  on  the  sides  of  which  there 
are  cells ;  their  form  is  exceedingly  elongated.  The  lungs  on 
one  side  is  often  much  smaller  than  the  other.  The  tongue  is 
long  and  slender,  and  forked  at  the  extremity ;  its  root  is  con- 
tained in  a  kind  of  sheath,  whence  it  can  be  protruded  and  re- 
tracted at  pleasure.  There  is  .properly  no  tympanum  belonging 
to  the  ear;  but  the  long  process  of  an  ossiculum  is  found  under 
the  skin,  and  is  connected  with  a  tympanic  bone. 

5.  Batrachia. 

1041.  The  batrachia,  (so  termed  from  the  Greek  name  of  the 
frog,  which  may  be  assumed  as  a  type  of  this  order,)  have  a 
heart  consisting  of  only  a  single  auricle  and  ventricle;  when 
arrived  at  maturity,  they  are  possessed  of  two  lungs ;  but  in  the 
earlier  stages  of  their  growth,  they  are  wholly  aquatic  animals, 
and  breathe  like  fishes  by  means  of  gills,  which  are  affixed  to 
the  sides  of  the  neck,  by  cartilaginous  arches  connected  with  the 
OS  hyoides.  Such  is  the  condition  of  the  tadpole,  which  is  the 
young  of  the  frog.  The  aorta,  on  its  exit  from  the  heart,  sends 
branches  to  each  of  the  gills ;  whence  the  blood  is  collected  by 
corresponding  veins,  that  unite  near  the  back  to  form  a  single 
arterial  trunk,  which  again  ramifies  and  distributes  the  blood  to 
every  part  of  the  body,  including  the  rudimental  lungs,  which 
are  not  yet  developed.  In  the  process  of  the  transformation  of 
the  tadpole  into  the  frog,  though  these  branchial  arteries  become 
obHterated,  yet  the  vessels  which  supply  the  lungs  remain,  and 
are  afterwards  the  channels  of  pulmonary  respiration. 

1042.  In  the  skeleton  of  the  frog,  in  place  of  ribs,  small  slender 
cartilages  affixed  to  the  extremities  of  the  transverse  processes 
of  some  of  the  vertebras,  which  in  the  dorsal  vertebrce  are  very 
broad.  The  spine  is  short,  and  terminates  behind  in  a  straight 
sacrum,  which  is  impacted  into  the  fork-shaped  or  innominatum. 
The  scapula  is  thin  and  flat ;  and,  together  with  the  clavicles,  are 
united  to  the  sternum;  but  as  there  are  no  ribs,  these,  with  the 
bones  of  the  anterior  extremities,  are  detached  from  the  rest  of 


REPTILES.  413 

the  skeleton.  There  are  properly  no  teeth ;  but  the  margin  of 
the  jaw  is  serrated.  The  urinary  bladder  exists,  and  is  even 
sometimes  double. 

1042.  Tlie  lungs  do  not  collapse  on  opening  the  chest ;  this 
arises  from  the  power  which  the  frog  possesses  of  distending 
them  by  the  muscles  of  the  mouth ;  the  respiration  being  con- 
ducted on  a  plan  similar  to  the  one  which  has  been  already 
described  in  the  tortoise  (§  1027).  Many  species,  as  the  pipa, 
have  the  vocal  organs  much  developed.  The  tongue  is  of  great 
length,  and  doubled  back  in  the  mouth  ;  it  is  thrust  forwards  to  a 
considerable  distance  in  seizing  its  prey,  and  retracted  with 
great  rapidity.  There  is  no  external  nieatus  to  the  ear  ;  but  the 
membrana  tympani  is  external,  and  appears  as  part  of  the  integu- 
ment."^ The  Eustachian  tube  opens  at  the  fauces  by  an  expanded 
mouth.  There  are  two  ossicula  auditus ;  and  the  vestibulum 
contains  rudiments  of  the  calcareous  bodies  met  with  in  other 
reptiles,  and  still  more  remarkably  in  fishes.  The  eye  has  two 
fleshy  eye-lids,  and  also  an  internal  nictitating  membrane,  which 
is  transparent  and  horizontal  in  its  direction. 

1043.  The  salamander  is  constructed  on  the  same  model  as 
the  frog,  with  regard  to  all  its  internal  organs ;  but  it  is  provided 
with  a  tail.  Its  ear  has  no  tympanum  ;  but  there  is  merely  a 
cartilaginous  plate  laid  over  the  fenestra  ovale  ;  there  is  no  third 
eye-lid.  The  skeleton  presents  small  rudimental  ribs,  but  no 
sternum.  This  animal  is  remarkable  for  the  power  it  possesses 
of  reproducing  the  parts  which  have  been  mutilated,  such  as 
entire  limbs  ;  and  even  the  eyes.  In  the  newt,  or  aquatic  sala- 
mander, the  lungs  have  numerous  processes,  as  in  the  chameleon, 
which  terminate  behind  in  an  elongated  bladder. 

Muller  has  lately  discovered  that  the  frog,  and  several  other 
animals  of  the  same  family,  are  provided  with  large  receptacles 
for  the  lymph,  situated  immediately  under  the  skin,  and  exhibit- 
ing distinct  and  regular  pulsations,  like  the  heart.  The  use  of 
these  lymphatic  hearts  is  evidently  to  propel  the  lymph  in  its 
proper  course  along  the  lymphatic  vessels.  Their  pulsations  do 
not  correspond  in  time  with  those  of  the  sanguiferous  heart;  nor 
do  those  of  the  right  and  left  sides  take  place  at  the  same  mo- 
ment ;  but  they  often  alternate  in  an  irregular  manner.* 

1044.  The  proteus  anguinus,  the  siren,  and  the  amphiuma,  are 
remarkable  for  possessing  both  gills,  Hke  the  tadpole,  and  lungs 
like  the  frog.  They  are,  accordingly,  adapted  for  living  both  in 
water  and  in  air;  and  are  the  only  animals  that  can  strictly  be 
said  to  be  amphibious.  The  eye  of  the  proteus  is  completely 
covered  by  the  integuments,  as  it  is  in  the  mus  typhlus. 

*  [Dr.  J.  J.  Allison,  of  Philadelphia,  has  also  observed  these  pulsating 
organs  in  the  tadpole,  the  frog,  in  the  sauria,  ophidia,  and  chelonia.  Amer. 
Journ.  of  the  Med.  Sciences,  for  Aug.  .1838.]  ^ 

35* 


414  COMPARATIVE    PHYSIOLOGY. 


Sect.  IV. — Comparative  Physiology  of  Fishes. 

1045.  Fishes  are  vertebrated  animals  with  red  blood,  breathing 
by  naeans  of  water  applied  to  the  gills,  or  hranchice,  which  in 
them  supply  the  office  of  respiratory  organs.  Their  powers  of 
motion  are  adapted  to  progression  through  the  medium  they  in- 
habit. This  design  is  conspicuous  in  the  form  of  their  bodies, 
the  great  muscularity  of  the  tail,  the  shortness  of  their  members, 
which  are  expanded  into  fins,  and  the  coverings  of  the  body, 
which  are  smooth  and  scaly.  The  oxygenation  of  the  blood, 
being  effected  solely  by  means  of  the  atmospheric  air  contained 
in  the  water  they  respire,  takes  place  only  to  a  small  extent; 
hence  the  temperature  of  the  body  in  fishes  is  not  sensibly  raised 
above  that  of  the  surrounding  medium,  and  these  animals  display 
little  energy  either  in  their  vital  or  their  sensitive  powers.  The 
brain,  accordingly,  is  of  small  size,  and  the  organs  of  the  external 
senses  but  little  developed  ;  they  scarcely  possess  any  organs 
calculated  to  convey  accurate  impressions  of  touch.  Nature  has 
denied  them  any  vocal  organs.  The  circumstances  in  which 
they  are  placed  would  appear  to  give  little  exercise  to  the  sense 
of  hearing ;  and  the  deep  recesses  of  the  ocean,  where  darkness 
eternally  reigns,  aflx)rd  as  little  to  that  of  sight.  No  lacrymal 
organs  are  wanted  by  animals  immersed  in  a  liquid  medium. 
The  voracity  with  which  fishes  devour  their  prey,  leaves  them 
scarcely  any  opportunity  of  discriminating  its  taste ;  and  their 
tongue  is  not  adapted  by  its  structure  for  receiving  the  impres- 
sions of  this  sense.  Neither  can  the  sense  of  smell  be  exercised 
in  the  same  degree  as  in  animals  respiring  atmospheric  air, 
through  which  odorous  emanations  are  so  extensively  and  so 
rapidly  diffiised.  Exclusively  occupied  in  the  two  great  objects 
of  animal  desire,  that  of  food  and  of  progeny,  all  their  movements 
appear  exclusively  directed  to  these  ends  ;  they  appear  insuscep- 
tible of  attachment,  and  incapable  of  any  but  the  lowest  degree 
of  intellectual  development. 

1046.  The  osteology  of  fishes  presents  a  very  complicated 
subject  of  study,  not  only  from  the  great  number  of  pieces  of 
which  their  skeleton  is  composed ;  but  also  from  the  great 
variety  of  forms  exhibited  in  the  different  genera  and  species  of 
this  class.  Fishes,  with  regard  to  their  skeleton,  admit  of  a  great 
primary  division  into  the  cartilaginous  and  osseous.  The  former, 
or  the  chondrojjterygii,  possess  no  real  bones,  but  merely  carti- 
lages, having  the  form  of  bones,  of  a  homogeneous  and  semitrans- 
parent  substance,  sometimes,  however,  as  in  the  rays  and  sharks, 
presenting  on  its  surface  small  calcareous  granules,  very  closely 
compacted  together.  In  a  few  fishes  arranged  under  this  division, 
as  the  sturgeon,  and  the  chimera,  we  meet  with  several  true 


FISHES.  415 

bones  in  the  head  and  shoulder,  while  the  rest  of  the  skeleton 

is  cartilaginous.  Even  among  the  strictly  osseous  fishes,  the 
density  of  the  bones  of  some  species  is  inferior  to  that  of  others, 
the  calcareous  substance,  or  phosphate  of  lime,  being  deposited 
in  fibres,  or  layers,  in  the  cartilage  which  serves  as  the  basis  of 
the  bone.  The  truly  osseous  fishes  have  bones  as  hard  and  as 
dense  as  other  vertebrated  animals ;  they  are  even  more  homo- 
geneous in  their  texture,  and  present  no  appearance  of  pores  or 
of  fibres,  as  are  seen  in  the  bones  of  the  mammalia.  We  never 
find  in  them  any  medullary  cavities. 

1047.  The  spinal  column  consists  of  dorsal  and  caudal  verte- 
brae only,  those  of  the  neck  and  sacrum  being  absent.  The  bodies 
of  vertebras  have  always  a  conical  depression  on  both  their  sur- 
faces; the  double  cone  thus  left  by  the  junction  of  their  margins 
being  filled  with  a  gelatinous  iiuid.  These  cavities  generally,  in- 
deed, communicate  together  throughout  the  whole  spinal  column 
by  apertures  in  the  centre  of  each  vertebra,  at  the  apices  of  the 
cones.  In  the  lamprey  this  opening  is  so  wide,  as  to  reduce  the 
vertebral  column  to  a  mere  series  of  rings,  traversed  from  one 
end  to  the  other  by  a  hgament.  The  spinous  processes  are 
usually  very  long,  and  their  roots  form  a  canal  for  the  passage 
of  the  spinal  cord.  Spinous  processes  are  also  frequently  found 
on  the  opposite  or  abdominal  side  of  the  vertebrae  ;  and  these 
also  form  a  canal  for  the  protection  of  the  aorta,  which  is  admitted 
through  it.  The  ribs  are  attached  each  to  a  single  vertebra,  and 
are  frequently  furnished  with  appendices  adhering  to  them  at 
one  end,  whilst  the  other  end  is  embedded  in  the  muscles. 

1048.  The  fins  of  fishes  do  not  present  much  analogy  with  the 
bones  of  the  extremities  of  quadrupeds,  although  such  analogies 
have  been  sought  with  much  eagerness.  The  fins  are  composed 
of  parallel  bones  called  rays,  which  are  connected  with  others, 
called  by  Cuvier  interspinal  hones,  and  by  Meckel  accessory 
spinal  apophyses.  The  sternum,  where  it  exists,  is  composed  of 
a  series  of  bones,  of  various  figures  in  different  fishes ;  but  which 
unite  the  lower  extremities'of  the  ribs.  In  the  pectoral  fin,  or 
anterior  extremity,  are  found  bones  somewhat  analogous  to  the 
two  bones  which  compose  the  scapula  of  reptiles ;  a  styloid  bone 
composed  of  two  pieces,  analogous  perhaps  to  the  clavicle  and 
coracoid  bone.  The  two  bones  corresponding  to  the  radius  and 
ulna  are  connected  with  a  row  of  ossicula  representing  the  carpus, 
and  which  support  the  rays  of  the  fin  itself 

1049.  The  posterior  extremity,  or  base  of  the  ventral  fin,  is 
composed  of  four  bones,  which  may  be  considered  as  a  pelvis; 
but  these  support  the  rays,  without  the  interposition  of  any  bones 
comparable  to  the  femur,  tibia,  or  tarsus. 

1050.  The  bones  of  the  head  are  exceedingly  complex,  and 
the  mere  enumeration  of  them  would  require  a  more  lengthened 
discussion  than  can  here  be  afforded.     The  bones  composing  the 


416  COMPARATIVE    PHYSIOLOGY. 

jaws,  namely,  the  maxillary  and  intermaxillary,  are  not  only 
moveable  on  the  skull,  but  also  on  each  other.  The  palatine,  the 
pterygoid,  and  the  tympanic  bones,  have  also  independent  motions. 
A  row  of  suborbitar  bones  also  exists,  different  from  what  is  met 
with  in  any  other  class.  To  the  bones  of  the  skull  are  joined  also 
the  opercular  system  of  bones,  which  protect  the  gills,  and  are 
subservient  to  the  motions  which  open  and  close  them  during 
respiration.  The  proper  bones  of  the  skull  are  placed  in  the  midst 
of  these  four  systems,  and  are  very  similar  to  those  of  reptiles, 
containing  a  receptacle  for  the  brain,  another  for  the  labyrinth  of 
the  ear,  and  others  for  the  eyes,  and  for  the  nasal  cavities.  The 
OS  frontis  is  composed  of  six  f)ieces ;  the  parietal  of  three ;  the 
occipital  of  five;  each  temxporal  of  two;  and  the  sphenoidal  of 
five.  Much  ingenuity  has  been  lavished  in  the  attempt  to  discover 
analogies  between  these  bones  and  the  parts  which  compose  the 
skeleton  in  the  other  classes  of  animals.  Thus  the  opercular  bones 
have  been  supposed  to  correspond  to  the  ossicula  auditus  of 
mammalia ;  a  notion  which,  although  ably  supported  by  Geoffroy 
St.  Hilaire,  may  perhaps  at  first  sight  appear  extremely  fanciful 
and  hypothetical,  and  which  Cuvier  represents  as  utterly  un- 
founded. 

1051.  The  teeth  of  fishes  exhibit  almost  every  possible  variety 
in  form,  number,  and  situation.  They  may  be  distinguished, 
according  to  their  position,  into  intermaxillary,  maxillary,  man- 
dibular, vomerian,  palatine,  pterygoid,  lingual,  branchial,  and 
superior  and  inferior  pharyngean.  Some  fish  have  almost  all 
these  denominations  of  teeth  ;  others  a  smaller  number,  and  a  few 
genera  of  fishes  are  entirely  destitute  of  teeth.  The  teeth  are 
generally  of  a  conical  and  incurvated  form,  like  so  may  hooks ; 
sometimes  the  points  are  so  small  and  united  as  to  resemble  a 
brush  or  file  ;  others  are  round,  or  club-shaped ;  others  present 
more  flat  surfaces,  like  a  mosaic  pavement.  Their  structure  is 
always  simple,  being  formed  by  a  single  pulpy  membrane,  which 
afterwards  ossifies  ;  and  is,  in  process  of  time,  replaced  by  a  new 
tooth.  This  successive  renewal  of  the  teeth  of  fishes  is  continued 
during  the  whole  period  of  their  lives.  The  degree  of  mastication 
given  to  the  food  depends,  of  course,  on  the  form  and  situation  of 
the  teeth. 

1052.  Deglutition  is  assisted  by  means  of  a  membranous  velum 
placed  behind  the  anterior  teeth.  There  is  no  appearance  of 
salivary  organs ;  unless  we  regard  as  such  a  soft  and  highly 
vascular  organ  found  in  the  palate  of  the  carp.  This  organ  is 
highly  irritable,  and  swells  in  a  remai'kable  manner  on  the  ap- 
plication of  any  stimulus;  it  perhaps  performs  the  function  of  an 
organ  of  taste. 

1053.  The  oesophagus  is  generally  very  short  and  capacious ; 
it  is  continued  into  the  stomach  without  anv  marked  line  of  se- 


FISHES.  417 

paration;  and  part  of  the  food  is  often  retained  in  the  oesophagus 
undigested,  until  room  can  be  made  for  it  in  the  stomach.  In  a 
few  fishes,  the  parietes  of  the  stomach  are  muscular,  so  as  to 
entitle  it  to  be  considered  as  a  gizzard.  The  intestinal  canal 
is  generally  very  short;  its  internal  coat  is  more  or  less  villous; 
there  is  never  any  coecum  ;  the  only  distinction  between  the  dif- 
ferent portions  of  the  canal  is  formed  by  a  valve  near  its  extre- 
mity ;  but  this  is  not  succeeded  by  any  dilatation. 

1054.  A  remarkable  structure  is  met  with  in  the  intestines  of 
rays,  sharks,  and  sturgeons ;  which  present  a  spiral  valve,  or 
duplicature  of  the  inner  coat,  running  nearly  the  whole  length  of 
the  canal.  A  great  number  of  blind  pouches,  or  appendices 
pyloricce,  as  they  are  called,  from  their  being  more  numerous  in 
the  beginning  of  the  intestine,  are  generally  found ;  their  office 
appears  to  be  to  secrete  a  quantity  of  mucous  fluid,  probably 
analogous  to  saliva,  or  to  the  pancreatic  secretion.  In  the  stur- 
geon, these  are  short  and  united  by  vessels  and  cellular  substance 
into  one  mass,  which  union  becomes  more  close  and  compact  in 
the  rays  and  the  sharks,  constituting  a  real  conglomerate  gland, 
having  a  single  excretory  duct. 

1055.  In  many  fishes,  namely,  in  the  ray,  shark,  sturgeon, 
lamprey,  and  salmon,  there  are  two  passages  opening  outwards 
from  the  general  cavity  of  the  abdomen,  at  the  sides  of  the 
termination  of  the  intestine.  The  use  of  these  passages  is  un- 
known. 

1056.  The  liver  is  of  considerable  size,  and  placed  more  on 
the  left  side ;  great  variety  exists  with  regard  to  its  shape  and 
the  number  of  its  lobes  in  different  fishes :  its  texture  is  softer 
than  in  quadrupeds  and  birds,  and  it  contains  a  large  quantity  of 
oil.  There  is  almost  always  a  gall-bladder  of  greater  or  smaller 
size.  The  hepatic  ducts  are  sometimes  very  numerous,  and  are 
successively  joined  to  the  cystic  ducts.  The  mesentery  is  incom- 
plete ;  and  is  often  prolonged  into  folds  containing  fat,  which 
folds  may  perhaps  be  considered  as  corresponding  to  an  omentun). 
Although  the  lacteals  are  numerous,  there  are  no  lymphatic  glands 
in  the  mesentery. 

1057.  The  lymphatic  vessels  are  very  distinct  in  other  parts 
of  the  body.  Fohman  has  succeeded  in  injecting  them  in  the 
gills.  Several  fishes  have  a  urinary  bladder,  which  is  situated 
behind  the  rectum  ;  in  other  instances  there  is  merely  a  common 
cloaca,  into  which  the  ureters  terminate.  The  kidneys  are 
more  voluminous  than  in  any  of  the  preceding  classes,  and  are 
often  joined  together  posteriorly  ;  there  are  no  suprarenal  glands. 
The  spleen  is  constantly  present,  and  occupies  various  situations 
in  the  abdomen. 

1058.  The  circulation  in  fishes  is  conducted  upon  a  very 
different  plan  from  what  it  is  in  reptiles.     There  is,  as  in  warm- 


418  COMPARATIVE    PHYSIOLOGY. 

blooded  animals,  one  complete  circulation  for  the  body  in  general, 
or  a  systemic  circulation;  and  another  for  the  organs  of  respi- 
ration ;  and  besides  this,  a  partial  circulation  for  the  hepatic 
system  of  organs ;  but  what  more  particularly  characterizes  this 
mode  of  accomplishing  that  function  is,  that  branchial  circulation 
is  the  only  one  which  is  effected  by  a  muscular  apparatus,  that  is, 
by  a  heart.  The  systemic  circulation  has  no  such  organ  for 
communicating  to  it  a  mechanical  impulse. 

1059.  The  muscular  apparatus  for  carrying  on  the  circulation 
in  fishes  consists  of  four  cavities,  namely,  the  sinus  venosus,  the 
auricle,  the  ventricle,  and  the  bulbus  arteriosus;  the  three  latter 
are  inclosed  in  the  pericardium,  and  may  be  said  to  constitute 
the  heart,  which  is  situated  underneath  the  pharyngeal  bones, 
and  between  the  bronchial  arches.  The  blood  returning  from 
the  veins  of  the  body  and  head,  is  collected  in  the  sinus  venosus, 
which  transmits  it  by  a  single  opening  into  the  auricle,  valves 
being  interposed  at  the  entrance.  The  auricle  discharges  its 
contents  into  the  ventricle,  which  again  propels  it  into  the  bulbus 
arteriosus,  whence  it  proceeds  along  the  bronchial  arteries  to  be 
•distributed  on  the  gills.  Thence  it  is  returned  by  the  bronchial 
veins,  which  unite  near  the  spine  to  form  a  single  arterial  trunk 
corresponding  in  its  oifice  to  the  aorta,  and  distributing  the  blood, 
by  a  succession  of  ramifications,  to  every  part  of  the  body.  The 
veins  from  the  digestive  organs  are  collected  into  the  vena  portaj*, 
which  as  usual  ramifies  through  the  liver ;  and  there  appears 
also,  from  the  observations  of  Mr.  Jacobson,  to  be  in  addition  a 
lesser  venal  circulation,  independent  of  either  of  the  former,  and 
analogous  to  what  has  already  been  observed  in  birds. 

1060.  The  vivifying  influence  of  the  air  contained  in  the  water 
which  is  applied  to  the  gills  of  fishes,  is  quite  as  necessary  for 
the  continuance  of  their  vital  functions,  as  that  of  atmospheric 
air  is  to  animals  of  the  preceding  classes;  and  fishes  perish  with 
equal  rapidity  as  mammalia,  when  their  natural  element  is  with- 
drawn. This  happens  whether  the  water  has  been  deprived  of 
its  air  by  boiling,  or  whether  the  absorption  of  air  from  the 
atmosphere  is  prevented  by  a  body  capable  of  intercepting  it, 
placed  on  the  surface  of  the  water.  It  appears  from  the  re- 
searches of  jMr.  Ehrmann,  that  some  fishes,  as  the  cobitis,  swal- 
low air,  which  passes  along  the  intestinal  tube,  where  it  loses 
oxygen  and  acquires  carbonic  acid.  Fishes  taken  out  of  the 
vs^ater  are  killed  not  so  much  from  the  want  of  oxygen,  as  in  con- 
sequence of  the  drying  of  the  branchias,  which  impedes  the  circu- 
lation of  the  blood  through  them.  The  water  is  taken  in  at  the 
mouth,  and,  after  acting  on  the  gills,  which  are  filamentous  organs, 
aflixed  in  rows  to  the  branchial  arches,  and  protected  by  the 
operculum,  is  discharged  through  the  branchial  openings  below. 
In  the  cartilaginous  fishes  there  are  several  openings  provided 
for  the  outlet  of  water,  at  the  side  of  the  head. 


FISHES.  419 

1061.  Most  fishes  possess  a  large  bladder  full  of  air,  called  the 
swimming  bladder,  placed  immediately  underneath  ihe  spinal 
column;  it  communicates  witii  the  oesophagus,  and  sometimes 
with  the  stomach,  by  a  canal,  called  the  ductus  jmeimaticus.  In 
the  carp,  there  are  valves  in  this  canal  which  only  allow  of  the 
passage  of  air  out  of  the  bladder.  In  many  fishes,  especially  in 
flat  fish,  no  such  air-bladder  exists.  Its  figure  is  very  various ; 
its  cavity  is  generally  simple;  but  it  is  sometimes  divided  by  a 
number  of  partitions.  A  glandular  body  is  met  with  in  the  coats 
of  this  bladder,  which  probably  secretes  the  air.  The  obvious 
intention  of  this  instrument  is  to  give  greater  buoj^ancy  to  the 
fish  when  the  air  is  present,  and  to  allow  of  a  sudden  increase  of 
specific  gravity  by  its  escape.  In  by  far  the  greater  number  of 
fishes,  however,  the  air-bladder  has  no  outlet  whatever.  In 
many  fishes  it  is  called  the  sound,  and  furnishes  the  best  kind  of 
jelly.  Isinglass  is  the  product  of  the  air-bladder  of  the  sturgeon. 
The  air  it  contains  is  usually  nitrogen  gas,  whh  a  small  propor- 
tion of  oxygen  and  carbonic  acid  gases.  The  swimming  bladder 
of  fishes  is  regarded  by  many  of  the  German  physiologists  as 
having  some  relations  with  the  function  of  respiration  ;  and  as 
being  the  rudiment  of  the  pulmonary  cavity  of  land  animals;  the 
passage 'of  communication  with  the  oesophagus  being  conceived 
to  represent  the  trachea.     (See  §  1022.) 

1062.  The  brain  of  fishes  is  remarkable  for  the  smallness  of 
its  size,  not  only  as  compared  with  the  total  bulk  of  the  animal, 
or  with  that  of  the  nerves  connected  with  it,  but  also  with  the 
cavity  of  the  cranium,  which  it  does  not  by  any  means  fill,  the  space 
left  being  occupied  by  an  oily  secretion,  and  by  loose  cellular 
texture.  The  disparity  is  less  observable  in  young  fish ;  for  it 
would  appear  that  the  growth  of  the  brain  does  not  keep  pace 
with  that  of  the  rest  of  the  body. 

1063.  The  several  parts  which  compose  the  brain  of  fishes  are 
more  detached  from  one  another  than  in  the  higher  classes,  and 
are  placed  in  a  consecutive  series.  The  foremost  lobules  give 
rise  to  the  olfactory  nerves,  or  rather  appear  as  the  bulbous 
enlargements  of  the  origin  of  these  nerves.  The  next  in  succes- 
sion are  solid  lobes,  which  give  origin  to  the  optic  nerves ;  be- 
hind these  we  find  larger  lobes  containing  a  ventricle,  wnth  a 
striated  eminence,  at  the  back  part  of  which  are  four  smaller 
tubercles  corresponding  to  the  corpora  quadrigemina.     Behind 

..  these  is  the  single  lobule  of  the  cerebellum,  and  below  are  two 
inferior  lobes.  The  optic  nerves  pass  before  these  lobes,  and 
always  decussate  in  their  course  to  the  orbits.  Between  these 
nerves,  and  in  front  of  the  inferior  lobes,  is  the  pineal  gland. 
Behind  the  cerebellum  are  also  two  lobes,  which  may  be  termed 
the  posterior  lobes.  There  is,  however,  much  difterence  of 
opinion  as  to  the  parts  in  the  human  brain  to  which  these  several 
portions  of  the  brain  of  fishes  are  analogous. 


420  COMPARATIVE    PHYSIOLOGY. 

1064.  Great  variety  is  met  with  in  the  size,  position,  and  direc- 
tion of  the  eyes  of  fishes.  In  general,  however,  they  are  large. 
There  are  neither  eye-lids  nor  lacrymal  organs,  and  the  globe  of 
the  eye  has  but  little  mobility.  In  the  ray  and  shark  tribes,  it  is 
supported  oa  the  end  of  a  moveable  cartilaginous  pedicle,  articu- 
lated with  the  bottom  of  the  orbit.  The  anabliss  has  the  cornea 
divided  into  two  by  an  opaque  Hne,  and  two  perforations  exist  in 
the  iris,  but  there  is  only  one  crystalline  lens,  vitreous  humor, 
and  retina.  The  crystalline  lens  is  completely  spherical,  and  of 
great  size^  so  as  to  leave  but  little  space  for  the  vitreous  humor, 
it  is  composed  of  concentric  laminee,  which  are  of  greater  density 
■as  they  approach  the  centre.  A  falciform  ligament,  commencing 
■at  the  entrance  of  the  optic  nerve,  following  its  curvature  down- 
wards, and  containing  vessels  and  nervous  filaments,  is  observa- 
ble; its  extremity  is  attached  to  the  capsule  of  the  crystalline 
lens.  In  some  fish  this  ligament  has  a  black  colour,  like  the 
marsupium  of  birds.  The  sclerotica  is  often  supported  by  osseous 
■or  cartilaginous  plates,  as  in  birds.  The  pupil  is  incapable  of 
altering  its  dimensions ;  in  the  rays  and  flat  fish,  its  border  is 
fringed  with  palmated  processes.  The  cornea  is  nearly  flat^  and 
there  is  but  httle  aqueous  humor. 

1065.  There  is  found  in  the  eyes  of  fishes  a  peculiar  body,  the 
memhrano  vasculosa  Halleri,  having  the  shape  of  a  horse-shoev 
situated  between  the  internal  layer  of  the  choroid  coat,  or  tunica 
Ruyschiana,  and  the  middle  layer ;  it  gives  origin  to  a  vascular 
membrane,  called  the  campanula,  which  proceeds  towards  the 
lens,  and  has  some  analogy  with  the  marsupium. 

1066.  The  gastrobranchus  appears  to  be  wholly  destitute  of 
any  organ  of  vision.  In  the  blind  murena,  no  trace  of  an  eye 
can  be  perceived  externally,  but  a  rudimental  organ  exists  beneath 
the  skin. 

1067.  The  ear  of  fishes  consists  only  of  the  parts  belonging  to 
the  labyrinth ;  and  these  organs  are  generally  suspended  in  a 
cavity  of  the  cranium,  which  is  a  part  of  that  in  which  the  ence- 
phalon  is  contained.  The  two  vertical  semi-circular  canals  are 
suspended  to  the  top  of  the  skull  by  a  vertical  ligament.  The 
oily  or  mucilaginous  fluid  which  surrounds  the  brain  has  free 
access  to  the  cavities  which  surround  the  membranous  labyrinth. 
The  three  semicircular  canals  are  dilated  into  ampuUee,  which 
receive  the  filaments  of  the  auditory  nerve.  There  is  an  appen- 
dix to  the  sinus  medianus,  or  principal  vestibular  sac,  termed 
the  utricle,  and  a  smaller  one  termed  the  cyticule.  The  hard 
calcareous  bodies  consist  of  one  in  each  of  these  cavities,  being 
three  in  number.    There  is  no  part  corresponding  to  the  cochlea, 

1068.  In  the  ray  there  is  a  spiral  tube,  wholly  within  the  skin, 
which  terminates  in  a  kind  of  finestra  ovale,  and  appears  to  be 
the  rudiment  of  an  external  meatus. 


FISHES.  421 

1069.  Many  fishes  present  the  extraordinary  phenomena  of  the 
development  and  accumulation  of  electricity  in  large  quantities, 
which  they  have  the  power  of  discharging  at  pleasure,  so  as  to 
give  strong  shocks  to  animals  coming  in  electric  contact  with 
them,  or  forming  part  of  the  circuit  of  the  discharge.  This  effect 
is  often  so  powerful  as  to  benumb  and  paralyse  their  assailants. 
The  electric  fishes  which  are  known  to  possess  this  power  in  a 
high  degree  are  the  electric  ray  {raia  torpedo),  the  electric  eel 
[gymnotus  electricus),  and  the  silurus  electricus,  or  malapterurus 
electricus.  The  first  of  these  are  met  with  principally  in  the 
Mediterranean  Sea ;  the  second  in  several  rivers  in  South  Ame- 
rica ;  and  the  last  in  the  Nile  and  Senegal  rivers.  Other  fishes, 
however,  are  known  to  be  electrical,  although  they  have  been 
less  studied  than  those  already  mentioned,  such  as  the  rhinobatus 
electricus,  trichinus  electricus,  and  teirodon  electricus. 

1070.  The  electrical  organs  of  the  torpedo  consist  of  a  great 
number  of  five  or  six-sided  prisms,  placed  on  each  side  of  the 
head  perpendicularly  to  the  surface,  and  occupying  the  whole 
thickness  of  the  animal.  Each  prism  consists  of  a  tube,  with 
membranous  sides,  surrounded  with  nerves  and  blood-vessels,  and 
containing  a  vast  number  of  extremely  thin  plates,  parallel  to  one 
another,  but  in  a  transverse  position;  the  intervals  are  filled  with 
a  gelatinous  fluid.  Three  large  branches  of  the  par  vagum,  and 
one  branch  of  the  fifth  pair  of  nerves,  are  distributed  to  these 
organs  on  each  side.  The  electrical  apparatus  of  the  gyinnotus 
and  silurus  are  disposed  somewhat  differently ;  they  are  two  in 
number  on  each  side,  and  extend  the  whole  length  of  the  fish 
from  the  head  to  the  tail.  One  of  these  is  situated  deeply,  and 
the  other  superficially ;  the  two  being  separated  by  a  membranous 
partition,  and  each  being  formed  of  horizontal  plates  distant  one- 
third  of  a  line  from  one  another,  with  septa  passing  perpendicu- 
larly between  them,  and  directed  fi'om  within  outwards,  and  a 
fluid  occupies  the  intervening  spaces.  Their  nerves  are  derived 
from  the  intercostals,  and  are  224  in  number. 

1071.  The  identity  of  the  agent  called  into  playby  these  organs 
with  electricity  is  beyond  all  doubt.  The  same  bodies  which 
conduct  or  intercept  the  transmission  of  the  latter,  have  the  same 
property  with  regard  to  the  former ;  and  shocks  are  propagated 
through  a  chain  of  several  persons,  when  those  at  the  extremities 
of  the  chain  touch  the  fish.  Electric  sparks  have  been  obtained 
by  Walsh  from  the  discharge  of  the  gymnotus  when  passed 
through  a  strip  of  tin  foil  gummed  to  a  piece  of  glass  and  cut 
through  in  the  middle.  Dr.  John  Davy*  has  obtained  electro- 
magnetic effects  from  the  torpedo,  by  the  test  of  the  galvanometer; 

*  Phil.  Trans,  for  1833  and  1834. 
36 


422  COMPARATIVE    PHYSIOLOGY. 

and  has  also  rendered  needles  naagnetic  by  the  electrical  discharge 
from  the  fish.* ' 

1072.  It  appears  that  the  power  of  producing  these  electrical 
discharges  is  quite  voluntary,  and  dependent  on  the  nervous 
influence;  for  it  does  not  take  place  every  time  that  the  fish  is 
touched,  and  it  wholly  ceases  on  the  destruction  of  the  brain,  or 
the  division  of  the  nerves.  The  animal  appears  to  have  the  power 
also  of  determining  the  direction  of  the  discharges ;  and  often, 
when  irritated,  it  refrains  from  giving  shocks.  The  destruction 
of  the  electric  organ  on  one  side  does  not  interrupt  the  action  of 
the  opposite  organ.  Dr.  Davy  states,  that  the  dorsal  surface  is 
charged  with  positive,  and  the  ventral  surface  with  negative 
electricity,  and  that  unless  both  surfaces  be  simultaneously  touched, 
no  shock  is  felt ;  and  Matteuci  and  Colladonf  arrived  at  the  same 
conclusion  by  experiments  made  with  the  galvanometer,  as  to  the 
direction  of  the  electric  currents.  Electric  fishes,  when  vigorous, 
exert  this  power  as  strongly  in  the  air  as  in  the  water.  We  are 
quite  in  the  dark  with  regard  to  the  theory  of  these  phenomena. 
Matteuci  imagines  that  the  source  of  electric  power  in  these  fishes 
is  in  the  brain ;  and  that  the  purpose  served  by  the  complex 
arrangement  of  parallel  plates,  with  intervening  fluid,  which 
composes  the  structure  of  the  electric  organs,  is  that  of  mere 
accumulation,  analogous  to  the  property  of  the  Leyden  phial. 

1073.  What  may  be  called  the  nasal  cavities  or  nostrils  of  fishes, 
are  placed  generally  in  front  of  the  head,  and  their  openings  are 
a  valvular  membrane  or  partition;  behind  this  is  found  an  elegantly 
plaited  membrane,  disposed  in  semicircular  folds,  on  which  the 
ramifications  of  the  olfactory  nerves  terminate. 


Sect.  V. — Comparative  Physiology  of  Mollusc  a. 

1074.  The  class  mollusca  comprehends  all  the  variety  of  what 
are  commonly  called  shell-fish,  together  with  the  animals,  such 
as  the  slug,  which  resemble  them  in  their  anatomical  character, 
but  which  are  not  furnished  with  shells.  Their  comparative 
anatomy  has  been  studied  M'ith  great  care  and  diligence  by  Cuvier, 
whom  chiefly  we  shall  follow  in  our  general  description  of  this 
class. 

1075.  The  mollusca  have  neither  articulated  skeleton  nor 
vertebral  canal.  Their  nervous  system  does  not  present  a  central 
spinal  cord,  but  merely  a  certain  number  of  medullary  masses, 
dispersed  in  diflferent  situations  in  the  body,  and  of  which  the 

*  [See  some  observations  by  Dr  Faraday  on  the  electric  conditions  of  the 
Raia  torpedo  and  Gymnotus  electricus,  in  Lend.  Med.  Gazette,  Jan.  26,  1839, 
p.  647.] 

f  Seances  de  I'Acad.  des  Sciences,  Oct.  1836. 


MOLLUSCA.  423 

largest,  which  may  be  designated  the  brain,  is  placed  near  the 
oesophagus,  where  it  is  connected  with  a  collar  of  nerves  that 
embraces  that  tube.  The  circulation  is  always  double,  like  that 
of  fishes,  that  is  to  say,  the  pulmonary  circulation  is  always 
complete  in  itself,  as  well  as  the  systemic.  But  the  muscular 
vt'ntricle,  or  heart,  is  not,  as  in  fishes,  placed  at  the  commencement 
of  the  former,  but  of  the  latter ;  it  impels  the  blood  not  into  the 
branchial  arteries,  but  into  the  aorta.  The  blood  is  either  white 
or  of  a  bluish  colour ;  and  it  contains  less  fibrin  than  that  of 
vertebrated  animals.  The  veins  probably  perform  the  office  of 
absorbents. 

1076.  The  muscles  are  endowed  with  great  irritability,  and 
retain  this  property  long  after  they  are  divided.  They  are 
attached  to  different  points  of  the  skin,  which  is  smooth  and 
moistened  with  a  viscid  liquor.  The  muscular  actions  produce 
contractions  and  inflexions  of  the  different  parts,  and  elongations 
of  others,  by  means  of  which  the  animal  is  enabled  to  accomplish 
different  kinds  of  progressive  motion,  whether  in  water  or  on 
land,  without  the  aid  of  articulated  members,  or  the  advantage 
of  solid  unyielding  structures,  Hke  the  bones  of  the  vertebrated 
classes.  These  movements,  however,  are  necessarily  less  rapid 
and  energetic,  and  less  perfectly  executed. 

1077.  A  leading  characteristic  of  the  structure  of  the  mollusca, 
consists  in  a  muscular  expansion,  connected  with  the  integument, 
which  envelopes  all  the  viscera,  and  is  hence  denominated  the 
cloak  or  mantle.  It  assumes  various  forms  in  the  different  genera, 
being  sometimes  contracted  into  a  flat  disc,  at  other  times  being 
folded  into  a  tube,  or  doubled  into  a  sac,  or  expanded  into  the 
form  of  fins  or  oars.  Most  frequently  we  find  a  calcareous  secre- 
tion formed  on  difl^erent  parts  of  one  or  both  of  the  surfaces  of 
the  mantle,  which  hardens  and  forms  a  layer  of  shell.  Succes- 
sive depositions  take  place,  occasioning  the  enlargement  of  the 
shell  in  different  directions;  when  the  shell  is  wholly  external  to 
the  animal,  it  serves  for  its  habitation  and  protection;  this  is  the 
case  with  the  testaceous  mollusca ;  in  others  which  have  no  such 
covering,  (or  the  naked  mollusca,)  there  frequently  takes  place 
an  internal  deposition  of  the  same  material,  forming  an  internal 
shell.  The  calcareous  matter  is  always  intermixed,  when 
deposited,  with  animal  matter,  which  is  sometimes  in  the  form  of 
a  distinct  membrane,  and  which  has  frequently  a  shining  or  irri- 
descent  appearance,  constituting  the  substance  known  by  the 
name  of  mother-of-pearl. 

1078.  Great  variety  exists  in  the  organs  of  the  digestive  func- 
tions, as  will  be  seen  by  the  examples  we  shall  give  in  speaking 
of  the  diflferent  orders  established  in  this  class  by  Cuvier. 


424  COMPARATIVE    PHYSIOLOGY. 

1.  Cephalopoda. 

1079.  The  various  genera  of  sepise  or  cuttle-fish,  are  compre- 
hended in  this  order. 

In  these  animals,  the  mantle  is  folded  so  as  to  form  a  sac 
enveloping  all  the  viscera ;  its  sides  being  more  or  less  extended 
into  fins.  The  head  alone  protrudes  from  the  sac ;  its  form  is 
round,  furnished  with  large  eyes,  and  with  long  processes  or 
tentacula,  flexible  in  every  direction,  endowed  with  great  muscular 
power,  and  having  on  the  surface  a  great  number  of  suckers,  by 
which  they  are  capable  of  adhering  with  great  force  to  the  objects 
to  which  they  may  apply  them.  These  tentacula,  or  feet,  are 
employed  by  the  animal  in  walking,  which  it  does  with  the  head 
downwards;  in  swimmiing,  which  it  executes  with  the  head 
turned  backwards  ;  and  also  in  seizing  hold  of  bodies,  for  which 
action  they  are  well  adapted.  Between  the  basis  of  the  feet  is 
placed  the  mouth  containing  strong  horny  mandibles,  resembling 
in  their  form  the  beak  of  a  parrot.  The  excretions  pass  out 
by  a  funnel-shaped  aperture,  situate  at  the  mouth  of  the  sac,  and 
near  the  head. 

1080.  The  pulmonary  organs  consist  of  two  branchise  situate 
within  the  sac,  one  on  each  side,  and  having  the  figure  of  a  fern 
leaf.  The  great  vena  cava,  on  arriving  near  them,  divides  into 
two  trunks,  terminating  in  two  muscular  ventricles  placed  at  the 
base  of  the  branchiae,  for  the  evident  purpose  of  propelling  the 
blood  with  more  force  into  the  branchial  arteries.  The  branchial 
veins  corresponding  to  these  arteries,  unite  in  a  third  ventricle 
situate  near  the  bottom  of  the  sac,  and  which  sends  the  blood 
forwards  through  the  aortic  system  as  usual.  Thus  there  may 
be  said  to  be  three  separate  hearts  in  the  cuttle-fish,  one  aortic 
and  two  branchial.  The  water  respired  enters  at  the  open  margin 
of  the  mouth  and  passes  out  by  the  funnel-shaped  aperture  already 
described. 

1081.  There  is  found  a  tongue,  of  which  the  surface  is  bristled 
with  sharp  horny  points  ;  the  ossophagus  is  dilated  into  a  crop, 
and  terminates  afterwards  in  a  gizzard,  equally  muscular  with 
that  of  a  granivorous  bird.  To  this  succeeds  a  third  stomach, 
which  is  membranous,  coiled  into  a  spiral  form,  and  receives  the 
bile  by  two  ducts  from  the  liver. 

1082.  A  singular  secretion  is  prepared  by  a  gland  in  this 
animal,  of  a  deep  black  colour,  resembling  ink,  which,  when  ef- 
fused, darkens  the  surrounding  water  to  a  considerable  distance, 
and  gives  the  animal  an  opportunity  of  escaping  from  its  pursuers. 
The  brain  is  large ;  a  nervous  ganglion  surrounds  the  oesophagus. 
The  optic  ganglions  are  very  large  ;  and  the  nerves  form  plexuses 
in  the  abdomen  and  in  other  parts.  The  eye  is  similar  in  its 
conformation  to  that  of  the  higher  classes  of  animals ;  but  the 


MOLLUSCA.  425 

ear  is  constructed  in  a  still  simpler  manner  than  that  of  fishes, 
having  neither  simicircular  canals  nor  external  meatus,  but  con- 
sisting merely  of  a  membranous  sac  lodged  in  a  cavity  near  the 
brain,  in  which  a  small  cretaceous  body  is  contained. 

2.  Gasteropoda. 

1083.  The  mollusca  which  have  a  shell  consisting  of  a  single 
valve,  compose  a  numerous  order,  a  familiar  example  of  which 
occurs  in  the  snail.  The  slug,  on  the  other  hand,  belongs  likewise 
to  this  order,  although  it  has  no  external  shell.  Mollusca  of  this 
description  are  termed  gasteropodous,  because  they  crawl  on  a 
flat  disc  placed  under  the  belly;  the  back  is  covered  with  the 
mantle,  which  is  of  greater  or  less  extent,  and  secretes  the  shell. 
The  head  comes  out  more  or  less  from  the  mantle,  under  which 
it  is  occasionally  retracted,  so  as  to  be  both  concealed  from  view, 
and  protected  from  injury.  A  small  number  of  tentacula,  from 
two  to  six,  appear  above  the  mouth,  but  do  not  surround  it.  The 
eyes  are  exceedingly  small,  and  sometimes  adhere  to  the  head, 
sometimes  to  the  base,  or  the  side,  or  the  extremity  of  the  tenta- 
cula ;  but  occasionally  none  are  found.  The  position  and  struc- 
ture of  their  respiratory  organs  varies  in  the  different  families  of 
this  order;  and  they  are  always  situated  under  the  last  turn  of 
the  shell  when  this  latter  has,  as  is  generally  the  case,  a  spiral 
form ;  and  they  receive  the  water  either  by  a  broad  opening 
under  the  mantle,  or  by  a  narrower  aperture,  and  often  through 
a  tube  formed  by  the  prolongation  of  the  mantle,  which  is  fre- 
quently protected  by  an  indentation  or  tubular  process  of  the 
shell.  A  further  protection  is  often  afforded  by  a  flat,  horny,  or 
calcareous  plate,  which  closes  the  shell  when  the  animal  has 
retired  within  it,  and  which  is  termed  an  operculum. 

^084.  Instead  of  branchrse,  the  pulmonary  gasteropoda  are 
provided  with  cavities  for  the  admission  of  atmospheric  air,  which 
they  respire  in  its  gaseous /orm.  These  cavities  are  opened  and 
closed  at  the  pleasure  of  the  animal,  the  mechanism  of  their 
respiration  consisting  in  these  movements. 

The  stomach  and  intestinal  canal  are  of  very  various  structure 
in  the  different  genera.  In  some,  as  the  scyllsea,  we  find  cutting 
teeth  implanted  in  the  coats  of  the  stomach  itself;  in  the  pleuro- 
branchus  there  are  four  stomachs,  like  those  of  ruminant  quadru- 
peds. The  aplysia  is  provided  with  a  very  capacious  crop, 
which  leads  to  a  muscular  gizzard,  armed,  moreover,  with  a 
number  of  cartilages  of  a  pyramidal  shape ;  a  third  stomach  suc- 
ceeds to  this,  having  its  inner  coat  lined  with  sharp  hooks ;  and 
a  fourth,  shaped  like  a  coecum ;  and  the  intestines  are,  besides, 
exceedingly  voluminous. 

Many  of  the  gasteropodus  mollusca  present  the  curious  phe- 

36* 


426  COMPARATIVE    PHYSIOLOGY. 

nomena  of  the  double  hermaphrodite  generation  formerly  adverted 
to  (§  781.)  Impregnation  of  the  ova  requires  the  union  of  two 
individuals,  the  female  organs  of  each  receiving  the  male  organs 
of  the  other,  and  the  fecundation  being  mutual.  This  is  the  case 
with  the  helix  and  the  lymneus. 

3.  Acephala. 

1085.  The  acephalous  mollusca,  so  named  from  their  having 
no  head,  have  all  the  vital  organs  enclosed  in  the  two  folds  of  the 
mantle,  which  shuts  like  a  portfolio,  leaving  apparent  only  the 
orifice  of  the  mouth ;  but  in  some  cases  the  mouth  is  here  pro- 
longed in  the  form  of  a  tube.  In  almost  every  case  each  of  the 
two  sides  of  the  mantle  is  covered  by  a  valve  of  shell,  so  as  to 
constitute  a  bivalve  molluscous  animal ;  in  another  tribe  the  shell 
is  multivalve.  The  brain  is  situated  immediately  over  the  mouth, 
and  consists  of  a  certain  number  of  small  ganglions.  The 
branchise  have  almost  always  a  laminated  form,  the  plates,  gene- 
rally four  in  number,  being  covered  with  a  net  work  of  blood- 
vessels. The  mollusca  of  ihis  order  are  unprovided  with  teeth, 
the  food  brought  by  the  water  being  received  into  the  mouth, 
and  swallowed  in  its  original  state,  whence  it  passes  into  the 
stomach;  sometimes  there  are  two  successive  cavities  perform- 
ing the  functions  of  the  stomach;  the  intestine  is  of  various 
length.  The  liver  surrounds  the  stomach,*  and  pours  its  secretion 
directly  into  the  cavity  by  several  apertures. 

1086.  A  large  fleshy  process,  resembling  in  appearance  a 
tongue,  and  which  has  been  compared  to  a  foot,  projects  from 
the  body,  and  by  the  varied  movements  of  which  it  is  capable, 
enables  the  animal  to  perform  a  slow  progressive  motion.  Mus- 
cles are  also  provided  foreclosing  the  shell,  and  they  generally 
pass  directly  from  one  valve  to  the  other ;  sometimes  there  are 
two  muscles,  but  commonly  only  one.  The  valves  are  separated 
by  the  force  of  an  elastic  ligament  placed  at  the  extremity  of  the 
hinge,  which  is  called  into  action  when  the  muscles  that  close 
the  shell  are  relaxed. 

1087.  The  threads,  or  byssus,  spun  by  many  acephalous  mol- 
lusca in  order  to  attach  themselves  to  rocks,  as  a  ship  is  moored 
by  her  cables,  is  another  peculiarity  in  these  animals,  and  parti- 
cularly of  the  genera  mytilus  and  pinna. 

1088.  In  many  mollusca  of  this  order  the  rectum  passes 
through  the  cavity  of  the  heart,  and  this  latter  organ  receives 
the  blood  from  the  veins  by  means  of  two  auricles. 

Some  acephala  are  hermaphrodite  ;  but  the  union  of  the  sexual 
organs  necessary  for  fecundation  takes  place  in  a  single  individual. 
This  occurs  in  the  holothinia. 

1089.  One  of  the  most  singularly  constructed  of  the  animals 


ARTICULATA.  427 

referred  to  this  division  of  mollusca  is  the  ascidia.  The  mantle 
and  its  envelope,  which  is  a  thick  and  cartilaginous  tunic,  form 
together  a  sac,  everywhere  closed,  excepting  at  two  orifices,  the 
one  corresponding  to  the  termination  of  the  intestine,  the  other 
leading  into  a  cavity,  of  which  the  sides  are  the  branchias,  and 
at  the  bottom  of  which  is  placed  the  mouth,  the  principal  viscera 
subservient  to  nutrition  occupying  a  second  cavity,  and  the  heart 
being  lodged  in  a  third.  The  principal  nervous  ganglion  is 
situated  between  the  two  external  orifices  of  the  sac. 

Sect.  VI. — Comparative  Physiology  of  Articulata. 

1090.  This  great  division  of  the  animal  kingdom  comprises  all 
those  tribes  possessing  what  may  properly  be  called  an  external 
skeleton ;  that  is,  a  series  of  rings  or  hollow  cases,  of  a  hard 
texture,  which  enclose  all  the  important  organs  of  the  body,  and 
which,  by  their  muscular  connexions,  allow  of  various  kinds  of 
movements,  at  the  same  time  that  they  afford  protection  to  all  the 
softer  tissues  of  which  those  organs  are  composed.  The  best 
idea  that  can  be  formed  of  this  mechanical  construction  may  be 
obtained  by  examining  the  body  and  the  limbs  of  a  lobster,  in 
which  it  will  be  seen,  that  contrary  to  what  obtains  in  vertebrated 
animals,  the  harder  parts  are  external,  and  the  muscles  are  within 
them,  a  construction  allowing  of  very  free  movements  of  the 
limbs. 

1091.  A  remarkable  degree  of  uniformity  prevails  with  regard 
to  the  distribution  of  the  nervous  system  in  all  these  animals. 
The  brain,  which  is  situated  above  the  oesophagus,  but  is  still  in 
the  head,  as  in  the  higher  classes  of  animals,  is  exceedingly 
small ;  and  after  sending  out  filaments  of  nerves  to  the  different 
parts  about  the  head,  is  connected  with  a  double  nervous  cord, 
which  encuxles  the  oesophagus,  and  runs  along  the  under  side  of 
the  animal,  being  joined  at  intervals  by  nodules  or  ganglia,  from 
which,  as  from  new  centres,  other  nervous  threads  radiate,  and 
are  variously  distributed  to  the  different  vital  organs,  and  to  the 
limbs.  Each  of  these  nervous  ganglia  appears  to  perform  the 
office  of  a  subordinate  brain  in  relation  to  the  system  of  nerves 
which  proceeds  from  it,  and  to  the  parts  of  the  body  supplied  by 
those  nerves,  so  that  when  the  animal  is  divided  into  several  por- 
tions, each  portion  seems  to  possess  its  own  independent  vitality. 
The  form  and  structure  of  the  digestive  organs  is  very  various; 
but  jaws  are  always  found,  and  their  motion  is  lateral  instead  of 
vertical,  as  in  vertebrated  animals. 

1.  Annelida. 
1092.  The  first  class  of  articulated  animals  are  the  annelida. 


428  COMPARATIVE  '  PHYSIOLOGY. 

or  worm-shaped  animals.  They  are  remarkable  for  possessing 
red  blood,  which  circulates  in  a  double  S3'stem  of  complicated 
vessels,  without  any  heart,  or  niuscular  ventricles.  The  body  is 
soft,  more  or  less  elongated,  and  composed  of  a  great  number  of 
segments.  The  foremost  of  these,  which  may  be  regarded  as 
the  head,  contains  the  lai'gest  of  the  ganglia,  or  brain,  the  mouth, 
and  the  principal  organs  of  the  senses.  The  branchiae  are  gene- 
rally external,  and  sometimes  uniformly  spread  on  the  surface  of 
the  body ;  and  at  other  times  are  confined  to  the  anterior' divi- 
sions. Tufts  of  hair  or  bristles  supply  the  place  of  feet.  The 
mouth  is  either  furnished  with  hard  jaws,  or  else  extended  in  the 
form  of  a  tube. 

1093.  The  leech,  which  is  referable  to  this  class,  has  a  very 
capacious  stomach,  nearly  of  the  size  of  the  whole  body,  or  rather 
a  series  of  pouches,  or  dilatations  proceeding  from  each  side  of 
the  central  cavity.*  Tentacula,  situate  on  the  head,  are  their 
principal  organs  of  touch;  and  the  small  black  points,  observable, 
in  some  tribes,  have  been  regarded  as  organs  of  an  imperfect  kind 
of  vision.  The  earth-worm  has  a  remarkably  complicated  appa- 
ratus for  circulation,  consisting  of  a  great  number  of  dilatations  of 
the  dorsal  vessel,  forming  a  series  of  hearts.f 

2.  Crustacea. 

1 094.  The  articulated  form  is  more  perfectly  developed  in  the 
Crustacea  than  in  the  annelida.  Their  blood  is  white,  and  is 
circulated  by  the  aid  of  a  muscular  ventricle,  or  heart,  situated 
■in  the  back,  propelling  it  through  an  arterial  system;  whence  it 
returns  by  a  system  of  veins,  which  collect  in  a  trunk  passing 
along  the  lower  part  of  the  abdomen.  In  some  species  the  heart 
assumes  a  very  elongated  shape.  There  are  always  organs 
termed  antennce,  or  feelers,  situated  in  front  of  the  head  ;  and  these 
are  generally  four  in  number.  The  jaws  are  of  complicated 
structure.  It  is  only  in  a  few  species  that  an  internal  ear  is  met 
with,  and  it  then  consists  of  a  sac  full  of  fluid,  in  which  a  calca- 
reous concretion  is  contained.  The  eyes  are  generally  two  in 
number,  often  placed  at  the  end  of  pedicles,  and  consisting  of  a 
great  number  of  facets,  each  provided  with  a  separate  cornea, 
retina,  and  branch  of  the  optic  nerve;  and  the  whole  constituting 
what  is  termed  a  composite  eye.  The  branchiae  are  of  a  pyramidal 
form,  composed  of  plates,  or  filaments,  or  feathery  tufts,  generally 
situated  at  the  base  of  the  legs. 

1095.  The  larger  genera  of  this  class,  as  the  lobster,  have  a 
horny  stomach,  with  strong  teeth  implanted  in  its  coats,  for  the 

♦  See  a  description  and  delineation  of  this  structure  in  the  Bridgewater 
Treatise  on  Animal  and  Vegetable  Physiology,  ii.  103.     [Amer.  edit.  ii.  77.] 
t  Ibid.  ii.  255.     [Amer.  edit.  ii.  184.] 


ARTICULATA.  420 

evident  purpose  of  breaking  and  bruising  the  shells  that  are 
swallowed.  All  these  animals  cast  off  their  shells  several  times 
in  the  progress  of  their  growth,  a  new  shell  being  successively 
formed  of  larger  dimensions  than  the  preceding,  and  adapted  to 
the  increased  size  of  the  animial. 

3.  Arachnida. 

1096.  The  third  class  of  articulated  animals,  or  the  arachnida' 
have  been  separated  from  that  of  insects  with  which  they  had 
been  before  associated  ;  being  distinguished  by  the  following 
peculiarities  in  their  conformation  and  economy.  They  have  a 
distinct  circulation  of  the  blood  by  means  of  an  elongated  dorsal 
vessel  performing  the  office  of  a  heart,  propelling  its  blood  into  a 
system  of  arteries,  and  receiving  it  back  again  from  a  system  of 
veins.  They  are  without  antennae,  but  are  provided  with  palpi. 
They  have  pulmonary  cavities  subservient  to  the  respiration  of 
atmospheric  air.  The  head  is  united  W'ilh  the  trunk  without  the 
intervention  of  any  neck.  The  mouth  is  armed  with  jaws ;  and 
there  are  several  simple  eyes  situated  on  the  upper  part  of  the 
head. 


4.   Insects. 

1097.  Nothing  can  exceed  the  endless  variety  of  forms  dis- 
played by  this  class  of  the  animal  creation.  Their  internal  ana- 
tomy and  economy,  however,  present  many  points  which  are 
common  to  the  whole  class.  There  is  no  other  trace  of  a  heart, 
than  a  long  cylindrical  tube  extending  along  the  back,  and  termed 
the  dorsal  vessel ;  but  which  seems  to  be  closed  on  all  sides,  and 
neither  to  give  out,  nor  to  receive  communicating  branches  of 
any  sort.  This  vessel  appears  to  contain  a  fluid,  which  is  irre- 
gularly undulated  backwards  and  forwards,  by  a  kind  of  pulsation, 
or  occasional  contraction  of  one  part  of  the  canal,  and  dilatation 
of  another.  It  had  been  supposed,  in  the  absence  of  any  visible 
blood-vessels,  that  nutrition  in  insects  is  performed  by  a  kind  of 
gradual  transudation,  or  imbibition,  as  it  has  been  termed.  Pro- 
fessor Carus,  however,  has  lately  made  the  discovery  of  a  distinct 
circulation  in  the  vessels  of  the  larvas  of  several  insects,  and  other 
observers  have  found  a  system  of  partial  circulation  in  even  later 
periods  of  insect  life.  But,  in  general,  in  the  last  stage  of  trans- 
formation, all  these  vessels,  excepting  the  dorsal  vessel,  become 
obliterated.*  There  being  neither  branchiae  nor  pulmonary 
organs  where  the  nutritious  fluids  could  receive  the  vivifying 

*  The  dorsal  vessel  of  the  sphinx  lio;ustri  is  delineated  in  the  Bridgewater 
Treatise  on  Animal  and  Vegetable  Physiology,  ii.  245.     [Amer.  edit.  ii.  177.] 


430 


COMPARATIVE    PHYSIOLOGY. 


influence  of  the  air,  a  complex  mode  of  respiration  is  resorted  to. 
Apertures  are  found  in  different  parts,  generally  along  the  sides 
of  the  body,  and  which  are  called  spiracles  or  stigmata.  These 
are  the  commencements  of  elastic  tubes,  which  remain  continually 
open,  and  which  are  subdivided  and  ramified  like  the  blood-vessels 
of  other  animals,  for  the  purpose  of  conveying  air  to  every  part 
of  the  system.     These  tubes  are'  termed  trachecs. 

1098.  Insects  are  unprovided  with  glands  for  effecting  secre- 
tions ;  that  purpose  being  answered  by  means  of  long  spongy 
vessels,  which  appear  capable  of  absorbing  the  materials  they 
require  from  the  general  cavity  in  which  they  float. 

1099.  The  temperature  of  insects,  like  that  of  other  animals 
said  to  be  cold-blooded,  varies  with  that  of  the  surrounding  me- 
dium ;  but  is  generally  one  or  two  degrees  higher.  In  bee-hives 
and  ant-hills,  a  much  higher  temperature  prevails.  This  is  proved 
by  an  elaborate  series  of  experiments  made  on  the  temperature 
oi  insects,  and  its  connexion  with  the  functions  of  respiration  and 
circulation,  by  Mr.  Newport.* 

1100.  Their  nervous  system  is  formed  upon  the  general  model 
already  described  (§  1091).  The  digestive  organs  admit  of  the 
greatest  possible  variety,  according  to  the  habits  and  particular 
kinds  of  food  consumed.  To  specify  all  these  diversities  would 
far  exceed  the  limits  assigned  to  us  in  this  work.  The  external 
organs  connected  with  the  limbs,  the  antennae,  the  mouth,  and 
the  different  functions  of  sense,  fall  more  properly  under  the 
consideration  of  the  naturalist,  inasmuch  as  they  furnish  the  best 
characters  for  the  distinction  of  genera  and  species,  and  for  per- 
fecting their  systematic  classification.  The  subject  is  rendei^ed 
infinitely  more  complex  in  consequence  of  the  metamorphoses 
which  the  same  insect  undergoes  in  passing  through  the  different 
stages  of  its  existence,  from  the  egg  to  the  larva,  the  nympha  and 
the  imago,  or  the  perfect  insect.  But  for  the  history  of  these 
changes,  we  must  again  refer  to  the  naturalist,  to  whose  province 
it  more  strictly  belongs  to  record  them.  We  must  content  our- 
selves with  mentioning  in  this  place  a  few  of  the  more  striking 
peculiarities  of  internal  conformation  which  are  observable  in 
some  of  the  insect  tribes. 

1101.  The  first  that  we  shall  point  out  is,  the  remarkable 
structure  of  the  digestive  organs  of  the  orthoptera,  an  order  of 
insects  which  comprehend  the  blatta,  or  cockroach,  and  the 
mantis  or  leaf  insect,  the  ear-wig,  the  locust,  the  grasshopper,  and 
the  cricket.  Their  stomachs  bear  some  analogy  to  those  of  ru- 
minant quadrupeds,  in  complication  at  least,  if  not  in  oifice.  The 
first  stomach,  or  crop,  is  membranous ;  to  this  succeeds  a  mus- 
cular stomach,  or  gizzard,  the  internal  surface  of  which  is  armed 

*  Philosophical  Transactions  for  1837,  p.  25. 


ZOOPHYTES.  431 

either  with  scales,  or  with  horny  teeth.  Around  the  pylorus 
there  extend  two  or  more  blind  pouches,  furnished  at  their  extre- 
mities with  numerous  vessels  conveying  bile.  Many  similar 
biliary  ducts  are  inserted  in  the  course  of  the  intestinal  canal.  It 
has  been  strongly  suspected  that  the  insects  in  which  these  com- 
plex stomachs  are  found,  actually  possess  the  power  of  ruminating 
their  food. 

1102.  The  abdominal  cavity  of  the  working  bee  presents  us 
with  two  stomachs,  together  with  the  intestine  and  the  poison 
bladder.  The  anterior  stomach  in  which  the  oesophagus  opens, 
is  the  receptacle  for  the  honey,  which  is  occasionally  returned 
into  the  mouth  in  order  to  be  stored  in  the  honey-cells,  as  a  ma- 
gazine of  food  for  the  winter.  The  next  stomach  is  destined  to  con- 
tain the  pollen,  or  material  gathered  from  the  antennae  of  flowers. 
Its  inner  coat  has  a  great  number  of  circular  folds.  Wax  is  a 
secretion  of  a  peculiar  kind  from  the  bee. 

1103.  The  alimentary  canal  of  the  caterpillar,  before  transfor- 
mation, consists  of  a  straight  and  capacious  tube,  of  which  the 
anterior  portion  is  somewhat  dilated  into  what  may  be  considered 
as  the  stomach ;  and  of  which  the  posterior  portions  form  a 
cloaca;  the  biliary  vessels,  which  are  four  in  number,  and  very 
long,  are  inserted  very  far  behind.  When  the  caterpillar  is 
transformed  into  a  butterfly,  this  alimentary  canal  is  much  dimi* 
nished,  both  in  its  diameter  and  length ;  the  first  stomach,  or 
crop,  is  situated  on  the  side  of  the  tube ;  there  is  next  a  second 
stomach  full  of  irregular  dilatations,  a  slepder  but  long  intestine, 
and  a  coecum  near  the  cloaca.* 

J  104.  The  nervous  system  undergoes  corresponding  changes 
during  the  transformation  of  insects,  the  ganglia  uniting  in  several 
places,,  so  that  their  number  is  much  diminished.f  The  external 
senses  of  insects  have  for  the  most  part  a  considerable  range  of 
action.  Organs  of  vision  are  almost  constantly  present,  but  those 
of  the  other  senses  are  but  imperfectly  known.  The  principal 
organs  of  touch  are  the  antennce,  which  probably  also  perform 
other  offices  relating  to  sensation,  of  which  we  have  no  certain 
knowledge. 


Sect.  VII. — Comparative  Physiology  of  Zoophytes. 

1105.  The  animals  which  occupy  the  lowest  division  in  the 
scale  of  life,  and  constitute  an  approach  to  vegetable,  namely, 
the  class  of  zoophytes,  present  us  with  much  simpler  forms  of 

*  These  successive  conformations  of  the  digestive  organs,  in  the  sphynx 

/is:ustri,  or  privet  hawkmoth,  are  delineated  in  the  Bridgevvater  Treatise  on 

Animal  and  Vegetable  Physiology,  ii.  217.  [Amer.  edit.  ii.  157.] 

t  Ibid.  ii.  547. 


432  COMPARATIVE   PHYSIOLOGY. 

organization  than  any  of  those  which  have  passed  under  our 
review^.  Yet  amongst  these  we  may  trace  gradations  in  the 
mode  in  which  the  more  refined  organs  of  the  animal  economy 
successively  disappear,  and  their  functions  are  supplied  by  other 
parts,  and  also  in  the  gradual  simpUfication  of  those  functions, 
till  we  appear  to  arrive  at  an  approximation  to  mere  vegetative 
existence.  The  great  characteristic  of  the  more  perfect  animals, 
the  circulation  of  the  fluids  in  vessels  which  distribute  them  to 
every  part  for  the  purposes  of  nutrition  and  secretion,  is  wanting 
in  zoophytes ;  or  if  any  traces  of  a  circulation  can  be  discovered, 
it  is  exceedingly  partial  and  limited  in  degree.  There  is  a  well 
marked  disposition  in  all  the  organs  to  assume  a  symmetrical 
arrangement  about  a  common  centre ;  being  either  disposed  in 
radii  proceeding  from  the  centre,  or  arranged  in  a  uniform  man- 
mer  round  the  circumference  of  a  circle.  In  those  instances  in 
which  a  nervous  system  can  be  traced,  which  is  the  case  oi^ily 
among  the  higher  order  of  echinodermata,  the  disposition  to  as- 
sume this  radiating  form  is  particularly  observable. 

1106.  Many  amongst  the  lowest  orders  present  us  with  the 
singular  spectacle  of  compound  animals,  associated  in  great 
numbers  for  the  purposes  of  a  common  defence  and  habitation, 
and  having  even  nutrition  in  common.  These  more  particularly 
constitute  an  approach  to  the  vegetable  kingdom. 

I.  Echinodermata. 

1107.  The  zoophytes  arranged  in  this  division,  which  are 
chiefly  the  asterias,  or  star-fish,  the  echinus,  and  the  holothuria, 
present  us  with  some  appearance  of  an  external  skeleton,  or  hard 
encasement,  consisting  of  parts  which  are  often  articulated 
together,  an  imperfect  vascular  system,  and  the  appearance  of 
a  system  of  nerves. 

1108.  The  rays  of  the  asterias  are  composed  of  numerous 
pieces,  which  have  been  compared  to  vertebras,  are  slightly  move- 
able upon  one  another,  and  allow  of  a  slow  flexion  of  the  entire 
ray.  It  is  hollowed  below  into  a  longitudinal  groove,  abounding^ 
in  perforations  for  the  passage  of  numerous  rows  of  short  tenta- 
cula,  which  perform  the  office  of  feet,  for  the  progressive  motion 
of  the  animal,  and  which  also  absorb  water,  and  convey  it  into 
the  general  internal  cavity  for  the  purpose  of  respfration.  The 
centre  of  the  star  is  occupied  by  a  large  stomach,  the  entrance 
to  which,  or  the  mouth,  is  below,  and  which  sends  out  two  pro- 
longations, or  coeca,  to  each  ray;  these  are  ultimately  ramified 
into  minute  vesicles,  suspended  by  a  membrane  which  performs 
the  office  of  a  mesentery. 

1109.  The  structure  of  the  echinus  is  still  more  complicated. 
The  calcareous  covering  of  the  body  has  a  globular  shape,  but 


ZOOPHYTES.  433 

is  composed  of  several  angular  pieces  joined  together,  and 
perforated  by  rows  of  lobes,  through  which  the  short  feet,  or 
tentacula,  protrude.  Besides  these,  there  are  a  multitude  of  spines 
articulated  to  the  surface  of  the  shell,  and  subservient  to  voluntary 
motion.  The  mouth  is  armed  with  five  teeth,  inserted  in  a  com- 
plicated apparatus  of  jaws,  resembling  a  pentagonal  lantern,  pro- 
vided with  numerous  muscles,  and  suspended  over  the  great  open- 
ing in  the  centre  of  the  lower  surface  of  the  shell.  The  intesti- 
nal canal  is  of  great  length,  and  forms  a  spiral  tube  attached  to 
the  interior  of  the  shell  by  a  mesentery.  A  double  vascular  sys- 
tems extends  the  whole  length  of  this  canal,  and  is  partly  spread 
over  the  mesentery. 

1110.  The  holothuria  resembles  in  its  structure  the  echinus, 
but  it  has  a  cylindrical  instead  of  a  globular  form.  The  respira- 
tory organ  is  ramified  like  the  branches  of  a  tree,  and  fills  and 
empties  itself  at  the  pleasure  of  the  animal.  The  mouth  has  no 
teeth,  and  is  only  protected  by  a  circle  of  calcareous  plates. 
The  intestine  is  very  long,  and  makes  many  folds,  being  also 
attached  to  the  sides  by  a  mesentery.  A  partial  circulation 
takes  place  in  a  double  system  of  a  very  complicated  arrange- 
ment of  vessels,  which  has  relation  exclusively  to  the  intestinal 
canal,  and  of  which  some  of  the  branches  are  interlaced  with 
the  arborescent  respiratory  tubes  already  described. 

2.  Entozoa. 

1112.  Very  little  is  known  concerning  the  physiology  of  in- 
testinal worms  ;  the  information  that  has  been  collected  being 
chiefly  of  a  negative  kind.  They  have  no  visible  respiratory 
organs,  and  no  apparent  nervous  system  or  organs  of  sensation : 
and  still  less  can  we  discover  any  traces  of  a  circulation.  The 
only  very  distinct  organs  are  those  belonging  to  the  functions  of 
nutrition  and  of  reproduction.  Some  naturalists,  indeed,  allege  , 
that  they  have  detected  some  filaments  of  nerves;  but  the  real 
nature  of  these  filaments  is  still  very  doubtful. 

1113.  The  alimentary  canal  may  in  most  intestinal  worms  be 
recognised  without  much  difficulty  ;  it  is  sometimes  enclosed  in 
an  abdominal  cavity,  but  at  other  times  apparently  passes  through 
the  solid  parenchyma  of  the  body.  In  some,  as  in  the  taenia,  or 
tape-worm,, we  may  discern  ramified  vessels  for  the  distribution 
of  the  nourishment;  but  these  are  not  seen  in  others.  The 
simplest  animal  of  this  tribe  is  the  globular  hydatid,  which  con- 
sists altogether  of  a  vesicular  sac  filled  with  a  transparent  fluid, 
and  with  an  indistinct  mouth  ;  but  without  any  other  apparent 
external  organ.  This  tribe  of  entozoa  exhibit  the  simplest  example 
of  the  gemmiparous  mode  of  reproduction  ;  the  young  appearing 
as  gemmae,  or  buds,  which  at  certain  periods  spout  from  the 

a? 


434  COMPARATIVE    PHYSIOLOGY. 

homogeneous  parenchyma  composing  the  body  of  the  parent,  and 
by  a  sort  of  vegetative  growth,  gradually  assume  the  form  of  the 
original  animal,  and  are  detached  when  capable  of  exercising  an 
independent  hfe. 

Some  of  the  entozoa,  as  the  taenia,  or  tape-worm,  are  capable 
of  being  multiplied  like  plants,  by  division ;  each  segment  re- 
sulting from  the  division  being  converted  into  an  independent 
animal,  acquiring  whatever  parts  may  have  been  deficient,  and 
after  a  time  admitting  of  further  subdivision,  with  a  repetition  of 
the  same  phenomena. 

3.  Acalepha. 

1114.  These  are  either  fixed  on  rocks,  or  float  in  the  sea; 
they  exhibit  more  or  less  of  a  fibrous  texture,  and  contain  vessels 
which  are  excavated  out  of  the  substance  of  the  body  itself,  and 
are  not  contained  in  any  distinct  cavity. 

1115.  The  actinia,  or  sea  anemone,  is  provided  with  numerous 
hollow  tentacula  surrounding  the  mouth  and  stomach.  The 
space  between  the  stomach  and  the  outer  skin  is  divided  into 
compartments  by  vertical  partitions,  and  the  fluid  contained  in 
these  compartments  may  be  projected  into  the  tentacula  so  as  to 
render  them  turgid. 

1116.  The  medusa  has  a  hemispherical  form,  and  a  gelatinous  * 
consistence.  The  mouth,  which  is  situated  in  the  centre  of  the 
flat  disc  below,  is  surrounded  by  fringed  tentacula.  It  leads  into 
a  singularly-shaped  cavity,  which  is  the  stomach,  formed  of  four 
arches  proceeding  like  radii  from  the  centre',  and  terminating  in 
tubes  which  are  variously  divided,  and  the  branches  derived  from 
them  freely  communicating  with  one  another  by  anastomoses. 
These  are  apparently  for  distributing  the  nourishment  which  has 
been  prepared  by  the  stomach,  but  not  for  any  real  circulation. 
There  are  four  large  cavities  in  the  body  which  appear  to  be 
subservient  to  respiration. 

1117.  In  some  species,  forming  the  genus  rhizostoma  of  Cuvier, 
there  is  no  central  mouth,  but  a  canal  commences  by  an  open 
orifice  from  the  extremity  of  each  of  the  fringe-like  processes  of 
the  tentacula,  and  these,  uniting  with  others  in  their  course  up- 
wards, form  at  length  a  single  tube  or  oesophagus,  w^hich  termi- 
nates in  the  central  stomach  already  described. 

Most  of  the  animals  of  this  order,  which  are  found  fixed  on 
rocks,  are  propagated  by  means  of  spores  or  gemmules,  consti- 
tuting one  of  the  modes  by  which  the  gemmiparous  form  of  re- 
production is  efiected.  These  gemmules  are  minute  bodies, 
formed  either  on  the  surface  or  in  some  special  internal  organ  of 
the  parent,  and  which  are  immediately  detached  and  swim  with 
a  spontaneous  and  independent  motion  in  the  circumambient  fluid. 


ZOOPHYTES.  435 

by  means  of  cilia  or  short  filaments,  which  are  in  rapid  and 
incessant  vibration.  They  ])ursue  these  motions  for  a  certain 
time  till  they  find  a  convenient  place  for  their  future  habitation, 
where,  when  they  are  once  fixed,  they  generally  remain  ever 
after,  growing  to  the  dimensions  and  exercising  all  the  functions 
of  the  parent  animal.  In  the  acalepha,  which  are  not  stationary, 
the  gemmules  retain  their  liberty  of  moving  during  the  whole 
period  of  their  existence. 

4.  Polypi. 

1118.  The  organization  of  this  numerous  order  of  zoophytes 
presents,  in  every  essential  particular,  great  uniformity,  and  bears 
a  great  analogy  to  that  of  the  actinia.  The  gelatinous  sac  or 
tube,  constituting  the  digestive  cavity,  is  closed  at  one  end,  the 
opening  at  the  other  end  being  the  mouth,  which  is  surrounded 
by  a  circle  of  tentacula ;  and  the  nutritive  fluid  passing  by  im- 
bibition through  the  coats  of  the  general  sac  or  stomach  for  the 
purpose  of  nourishment.  The  hydra  may  be  taken  as  the  type 
of  this  tribe  of  animals.  It  consists  of  a  mere  stomach  provided 
with  flexible  tentacula  for  catching  food  and  for  progression. 
This  sac  may  be  inverted  or  turned  inside  out,  without  detriment 
to  the  animal,  digestion  being  then  performed  by  the  new  cavity, 
which  is  the  result  of  the  operation.  These  animals  present  the 
simplest  examples  of  gemmiparous  generation  (§  777). 

No  further  discovery  can  be  made  respecting  the  organization 
of  these  animals,  even  by  applying  the  microscope,  which  shows 
only  a  semitransparent  substance  interspersed  with  opaque  grains. 
The  greater  number  secrete  on  their  outer  surface  a  calcareous 
or  a  horny  substance,  which  serves  for  their  mechanical  support, 
but  at  the  same  time  fixes  them  on  the  spot  to  which  they 
adhere. 

1119.  The  most  remarkable  feature  in  their  history  is  their 
disposition  to  congregate  together  in  vast  numbers,  so  as  to 
compose  by  their  united  architecture  whole  rocks  and  even 
submarine  mountains,  rising  from  the  bottom  of  the  ocean.  Some 
of  these  animal  republics  exhibit  amongst  the  individuals  thus 
associated  together  communications  of  nutritious  vessels,  so  that 
the  materials  for  the  sustenance  of  each  passes  into  the  bodies 
of  the  neighbouring  polypi,  and  is  applied  to  the  purposes  of  their 
economy.  All. these  fixed  polypi  are  propagated  by  spores  or 
gemmules  in  the  manner  already  described  in  our  account  of  the 
stationary  acalepha. 

5.  Infusoria. 
11.20.   These  being  all  microscopic  animalcules  of  extreme 


436  HISTORY   OF   PHYSIOLOOr. 

minuteness,  it  is  scarcely  possible  to  arrive  at  any  exact  know- 
ledge of  their  internal  organization  or  economy.  Many,  and  pro- 
bably all,  are  possessed  of  distinct  organs  for  the  reception  of 
food,  for  reproduction,  and  for  voluntary  motion  ;  but  conjecture 
alone  can  fill  up  the  imperfect  outline,  or  suggest  any  plausible 
hypothesis  as  to  their  powers  of  sensation,  which,  however,  we 
are  unwilling  to  refuse  to  any  being  which  appears  to  possess 
the  properties  and  attributes  of  animality,  especially  since  the 
splendid  discoveries  of  Ehrenberg  have  made  us  acquainted  with 
the  complex  organization  observable  in  some  of  the  minutest  of 
this  prodigiously  diversified  tribe  of  beings.  It  is  remarkable, 
indeed,  that  those  very  animalcules,  as  the  monads,  Mdiich  had 
been  ranked  by  naturalists  among  the  agastrica,  or  beings  totally 
without  alimentary  cavities,  are  now  found  to  have  a  very  consi- 
derable number  of  stomachs,  and  to  be  entitled  accordingly  to 
the  title  oi  polygastrica. 

It  is  chiefly  amongst  the  various  tribes  of  infusoria  that  the 
simpler  modes  of  generation,  such  as  that  termed  fssijparous,  are 
exemplified.  In  the  monas,  for  instance,  a  groove  is  seen  to  form 
around  the  equator  of  their  globular  bodies,  which  groove,  gra- 
dually deepening,  changes  their  form  to  that  of  an  hour-glass,  and 
the  connecting  ligament  of  the  two  portions  being  soon  broken, 
the  segments  move  away  from  one  another,  each  commencing 
its  independent  existence,  and  being  capable  of  performing  all 
the  functions  of  the  undivided  monad.  In  the  bell-shaped  vorti- 
cella,  the  division  commences  at  the  mouth  or  wide  extremity  of 
the  bell,  and  gradually  extends  in  a  longitudinal  direction  towards 
the  insertion  of  the  stem,  dividing  the  body  into  two  equal  por- 
tions, each  being  now  a  distinct  and  individual  animal.  The 
gonium  divides  itself  into  four  instead  of  two  portions,  each  por- 
tion being  again  subdivided  into  four  others,  the  new  animalcules 
assuming  rapidly  the  dimensions  and  appearance  of  the  one  of 
which  they  originally  formed  a  part.  Other  species  are  propa- 
gated by  means  of  gemmules ;  and  some  of  the  infusoria  are 
apparently  oviparous- 

1^'    '■^■'  QmL^^R  XXIV. 


\     trx     ^^L  '"^  *  *  "^  ihs^Jr^^f  physiology. 

V,&\_       -    -^     "* 

Nl^t^he  study  of  the  history  of  any  science  furnishes  to  the 
mind  aFody  of  knowledge  not  merely  ornamental  or  superfluous, 
but  one  that  is  fraught  with  instruction  and  utility,  and  is  condu- 
cive to  the  just  comprehension  of  the  subject  to  which  it  relates. 


HISTORY   OF   PHYSIOLOGY.  437 

It  is  scarcely  ever  necessary,  indeed,  for  the  understanding  of 
any  proposition,  that  the  student  should  follow  the  same  laborious 
course  and  travel  through  the  same  tortuous  mazes  by  which  the 
discovery  had  originally  been  achieved ;  for  the  acquisition  of 
any  body  of  knowledge  already  systematized  by  the  labours  of 
our  predecessors,  is  in  general  most  readily  attained  by  the 
synthetic  method.  But  as  soon  as  this  point  has  been  reached 
we  can  conceive  no  course  of  study  more  calculated  to  improve 
that  knowledge,  and  to  invigorate  the  faculties  by  which  it  may 
be  extended  and  perfected,  than  reverting  to  the  analytic  process, 
and  following  the  series  of  discoveries  in  the  order  in  which  they 
have  actually  occurred.  From  an  historical  survey  of  the  succes- 
sive steps  by  which  science  has  proceeded  from  a  rude  origin  to 
its  present  state  of  advancement,  and  which  mark  its  varied 
progress  and  even  occasional  retrogressions  at  different  periods, 
according  to  the  prevailing  disposition  of  the  age,  either  to  a 
servile  submission  to  authority  or  to  the  hasty  adoption  of  crude 
and  visionary  theories,  we  are  enabled  to  derive  most  important 
rules  for  the  conduct  of  the  understanding  in  the  search  after 
truth. 

The  history  of  each  particular  branch  of  science  may,  indeed, 
be  regarded  as  a  separate  chapter  in  the  history  of  the  human 
mind.  It  indicates  the  sources  of  its  activity  and  of  its  strength, 
and  also  of  its  weakness  and  fallibility ;  it  holds  out  the  most 
powerful  incentives  to  exertion  ;  it  exhibits  much  to  admire  and 
to  emulate,  and,  at  the  same  time,  discloses  enough  to  check  pride 
and  teach  humility. 

1122.  The  history  of  physiology  must  necessarily  comprise  a 
large  portion  of  the  history  of  anatomy,  which  consists  in  the 
mere  knowledge  of  the  organs  and  minute  structure  of  the  body, 
such  knowledge  being,  in  fact,  the  foundation  on  which  the  higher 
science  of  the  philosophy  of  life  is  built.  It  is  scarcely  possible, 
indeed,  to  study  mere  organization,  without  extending  our  views 
to  the  functions  that  we  see  performed,  and  to  the  energies  that 
are  exerted  by  the  living  organs.  Our  object  will  therefore  be  in 
the  present  place,  to  inquire  how  far  these  higher  qualities  of  mind 
have  been  displayed  by  the  cultivators  of  this  department  of 
knowledge  at  different  periods,  so  as  to  mark  the  progress  of  the 
philosophy  of  life,  as  contradistinguished  from  the  more  mechan- 
ical, though  equally  useful  labours  of  the  mere  anatomist. 

1123.  The  phenomena  which  constitute  the  subjects  of  physio- 
logical inquiry  must,  indeed,  have  attracted  the  attention  of 
mankind  long  before  any  accurate  knowledge  had  been  acquired 
of  the  structure  of  the  organs  whose  actions  give  rise  to  these 
phenomena.  Life  in  its  different  forms  must  have  been  familiar 
to  all ;  and  every  savage  and  warlike  people  must  have  been 
conversant  with  the  diversified  aspects  of  death,  which  they 

37* 


438  HISTORY  or  physiology. 

inflicted  in  such  various  modes.  Speculations  on  the  nature  of  the 
vital  principle,  and  the  physiological  conditions  on  which  it  is 
dependent  for  its  origin,  maintenance,  and  decay,  must  have 
been  formed  and  pursued  in  every  state  of  society,  removed  but 
one  degree  from  barbarism;  and  such  speculations  must  have 
stimulated  inquiry  into  the  internal  mechanism  with  which  that 
principle  is  associated,  and  the  hidden  springs  which  regulate  its 
course- 

1124.  Opportunities  mhst  frequently  have  occurred  in  the 
rudest  ages,  of  observing  the  different  parts  of  the  structure  of 
the  bodies  both  of  men  and  animals.  The  curiosity  even  of  the 
savage  could  not  fail  to  be  attracted  by  the  remarkable  appear- 
ance of  the  internal  organs,  in  the  animals  which  he  slaughtered  for 
food,  or  prepared  for  sacrifice.  Although  deterred  from  the  actual 
examination  of  the  human  body,  by  an  instinctive  repugnance, 
or  superstitious  terror,  various  casualties  occurring  in  battle,  or 
arising  from  accidents,  would  occasionally  afford  an  insight  into 
the  human  frame.  Human  bones,  and  sometimes  entire  skeletons^ 
would  often  present  themselves  to  those  who  revisited  the  fields 
of  carnage.  Thus  would  the  principal  bones,  and  the  most  con- 
spicuous viscera  of  the  human  body,  soon  become  known,  and 
they  would  be  designated  by  particular  names.  Evidence  to 
this  effect  may  be  collected  from  the  rudest  and  most  ancient 
languages ;  from  which  we  may  infer  that  a  certain  progress 
must  have  been  made  in  this  kind  of  knowledge,  long  before  it 
had  been  so  arranged  and  methodized  as  to  deserve  the  name  of 
a  science. 

1125.  The  prevailing  custom  amongst  most  of  the  ancient 
nations,  of  consigning  all  dead  bodies  to  destruction  by  fire,  was 
one  of  the  greatest  obstacles  to  the  advancement  of  anatomical 
and  physiological  knowledge.  But  opportunities  were  on  the 
other  hand  afforded  of  learning  the  structure  of  certain  animals, 
by  the  religious  rites,  during  the  celebration  of  which  these 
animals  were  sacrificed,  and  especially  by  the  examinations  which 
were  made  by  the  priests  of  the  yet  palpitating  entrails  of  their 
victims,  for  the  purpose  of  prognosticating  future  events.  Infe- 
rences were  thus  drawn  by  analogy  as  to  the  organization  and 
functions  of  the  human  body.  The  Egyptians,  indeed,  who 
composed  the  most  ancient  nation  of  whose  manners  and  customs 
we  possess  any  authentic  records,  were  supposed  to  have  acquired 
considerable  knowledge  of  the  human  structure  from  the  practice 
of  embalming  the  dead.  This  operation  was  performed  by  a 
particular  class  of  men,  and  consisted  in  taking  out  a  portion  of 
the  viscera,  washing  them  with  antiseptic  fluids,  and  filling  the 
cavities  with  aromatic  substances.  But  as  this  process  appears 
to  have  been  conducted  in  the  rudest  manner,  it  required  no  skill 
in  anatomy,  and  was  but  little  calculated  to  improve  the  science. 


HISTORY   OF    PHYSIOLOGV.  439 

It  was  in  the  hands  of  a  few  persons  only ;  and  such  was  the 
contempt  and  abhorrence  in  which  these  persons  were  held  by 
their  countrymen,  that  whatever  knowledge  they  might  have 
acquired  by  the  practice  of  their  art,  was  not  likely  to  be  com- 
municated to  others. 

1126.  Whatever  splendour  may  have  attended  the  pride  of 
power  or  extent  of  empire  in  these  rude  and  unenlightened  ages, 
the  dawn  of  science  was  coeval  only  with  that  of  liberty.  The 
same  energies  by  which  man  had  thrown  off  the  yoke  of  tyrann)^ 
animated  them  likewise  with  the  desire  of  knowledge ;  and  na- 
tions had  no  sooner  emancipated  themselves  from  despotism,  than 
they  began  to  emerge  from  barbarism  and  ignorance.  The 
Greeks,  who  were  the  most  free,  were  also  the  most  polished  of 
all  the  nations  of  antiquity,  and  far  excelled  them  in  every  species 
of  science  and  of  art.  So  great  was  the  ardour  of  their  philo- 
sophers in  the  pursuit  of  knowledge,  that  they  frequently  travelled 
into  distant  countries  to  collect  useful  information,  and  impart  it 
to  their  pupils.  Even  in  the  time  of  Homer,  the  Greeks  seem  to 
have  possessed  much  general  knowledge  both  of  anatomy  and 
physiology,  as  may  be  collected  from  the  writings  of  that  poet. 
He  relates  that  the  stone  which  was  hurled  at  vEneas  by  Diomed, 
not  only  crushed  the  thigh-bone,  but  also  tore  the  ligament  of  the 
acetabulum.  Morion  is  represented  as  being  wounded  in  one  of 
the  large  veins  which  return  the  blood  to  the  heart,  or  venag 
cavee ;  and  Ulysses  aimed  a  blow  at  the  Cyclops  at  the  part 
where  the  liver  adheres  to  the  diaphragm.  It  has  even  been 
supposed  that  Homer  has  purposely  often  wounded  his  heroes 
that  he  might  have  opportunities  of  displaying  by  the  minuteness 
of  his  descriptions,  his  accurate  acquaintance  with  anatomy. 

1127.  But  though  curiosity  was  roused,  and  a  multitude  of 
detached  facts  had  been  observed  and  collected,  it  was  long  be- 
fore the  proper  methods  of  investigation  were  known,  and  the 
true  principles  of  inquiry  established.  Although  it  appears  that 
the  studies  of  anatomy  and  physiology  were  prosecuted  with 
considerable  ardour  in  the  school  of  Pythagoras,  yet  as  they 
were  regarded  merely  as  a  part  of  natural  history,  the  informa- 
tion relating  to  these  subjects  was  not  sutSciently  connected  or 
concentrated  to  be  embodied  in  one  science.  Alcmeon  and 
Empedocles,  who  cultivated  anatomy,  belonged  to  this  school ; 
but  the  most  remarkable  of  the  pupils  of  Pythagoras,  belonging 
to  the  Eleatic  sect,  was  Democritus  of  Abdera,  a  man  whose 
eccentric  manners,  as  well  as  penetrating  genius,  and  undisguised 
contempt  for  the  follies  of  mankind,  have  procured  him  so  much 
celebrity.  He  is  said  to  have  devoted  considerable  time  to  the 
dissection  of  animals,  especially  with  a  view  to  discover  the 
origin  and  course  of  the  bile.  His  fondness  for  seclusion,  and 
his  perseverance  in  a  pursuit  which  appeared  to  his  countrymen 


440  HISTORY   OF    PHYSIOLOGY. 

to  be  without  any  rational  object,  led  them  to  suspect  the  sound- 
ness of  his  intellects ;  and  Hippocrates  was  sent  to  visit  him  in . 
his  solitary  abode.  He  found  the  philosopher  seated  on  a  stone, 
under  the  ample  shade  of  a  plane  tree,  with  a  number  of  books 
arranged  on  each  side,  one  on  his  knee,  a  pencil  in  his  hand,  and 
several  animals  which  he  had  been  dissecting  lying  before  him. 
His  complexion  was  pale,  his  countenance  thoughtful ;  at  times 
he  laughed,  at  times  shook  his  head,  mused  for  a  while,  and  then 
wrote,  then  rose  up  and  walked,  inspected  the  animals,  sat 
down,  and  wrote  again.  Hippocrates,  who  perceived  the  nature 
of  his  inquiries,  observed  him  for  some  time  in  silent  admiration, 
proclaimed  to  the  bystanders  the  importance  of  his  researches, 
and  declared  to  them  his  regret  that  want  of  leisure  from  his 
own  professional  employments  did  not  allow  him  to  engage  in 
similar  pursuits. 

1128.  But  it  was  only  from  men  whose  minds  are  capable  of 
enlarged  views,  and  can  perceive  the  bearings  and  connexions 
of  the  several  parts  of  the  subjects  they  embrace,  that  a  powerful 
impulse  is  given  to  science,  such  as  to  make  it  almost  the  crea- 
tion of  their  hands,  that  it  is  raised  to  its  proper  rank  among  the 
departments  of  human  knowledge.  Such  was  the  vigorous  mind 
of  Hippocrates  ;  and  so  great  was  the  improvement  which  medi- 
cine derived  from  his  genius,  that  the  foundation  was  thus  laid 
for  the  more  rapid  progress  of  all  the  sciences  connected  with  it 
in  succeeding  times.  Hippocrates  was  born  in  the  island  of  Cos, 
in  the  first  year  of  the  80th  olympiad,  or  460  years  before  Christ; 
an  era  which  is  therefore  remarkable  in  the  history  of  medical 
science.  It  appears  that  at  that  period  a  knowledge  of  medicine 
had  been  in  a  great  measure  hereditary  in  certain  families, 
amongst  whom  the  information  which  had  descended  from  the 
successive  generations  was  thus  retained  and  augmented.  This 
was  the  case  in  the  family  of  Hippocrates,  who  is  said  to  have 
been  the  fourteenth  descendant  from  Esculapius,  on  his  father's 
side  ;  while  his  maternal  ancestry  could  be  traced  to  Hercules. 
He  had  been  instructed  in  all  the  learning  of  those  times  ;  but 
particularly  dedicated  himself  to  the  cultivation  of  medicine, 
which  he  formed  into  a  distinct  science,  collecting  and  arranging 
all  the  information  on  the  subject  that  was  then  known.  Not 
satisfied  with  the  knowledge  which  he  could  acquire  in  his  native 
place,  he  travelled  for  several  years  through  difl^erent  parts  of 
Greece  and  Asia  Minor.  He  visited  the  temple  of  Diana  at 
Ephesus,  and  was  at  the  pains  of  transcribing  and  arranging  the 
records  of  cases  and  of  successful  methods  of  pure,  which  it  was 
the  custom  to  deposit  on  tablets  in  these  temples.  On  retiring  to 
his  native  island,  after  the  laborious  proofs  he  had  given  of  his 
diligence  and  ardour,  he  continued  to  exercise  his  profession,  and 
enjoyed  the  highest  and  most  extensive  reputation.     Such  was 


HISTORY    OF   PHYSIOLOGY.  441 

the  estimation  in  which  his  talents  were  held,  that  even  princes 
were  soHcit'ous  to  allure  him  to  their  courts ;  but  he  was  so 
strongly  attached  to  his  native  country,  that  he  resisted  every 
temptation  which  the  splendour  or  the  favour  of  monarchs  could 
hold  out. 

1129.  Excepting  one  or  two  particular  treatises,  which  bear 
his  name,  but  the  authenticity  of  which  is  dubious,  the  writings 
of  Hippocrates  are  to  be  regarded  rather  as  medical  than  phy- 
siological ;  but  he  seems  to  have  been  the  first  who  formed  a 
clear  conception  of  the  value  of  anatomy  and  physiology  as  the 
basis  of  medical  reasoning.  #-  Originality  of  thought,  combined 
with  accuracy  of  observation,  forms  the  characteristic  feature  of 
his  writings ;  which  contain,  however,  many  traces  of  the  Pytha- 
gorean philosophy,  with  which  he  seems  to  have  been  early 
imbued.  He  formed  the  bold  conception  of  the  existence  of  a 
principle,  which  he  calls  ?i/3-«,  or  nature,  exercising  a  general 
direction  and  superintendence  overall  the  actions  and mov^ements 
of  the  body,  and  endowed  for  that  purpose  with  a  species  of 
intelligence  directed  to  beneficial  ends.  As  subservient  to  this 
great  and  prime  agent,  he  imagined  that  the  functions  were  car- 
ried on  by  means  of  other  subordinate  powers  or  faculties;  and 
also  that  they  were  subjected  to  the  influence  of  the  stars.  He 
regarded  the  body  as  being  composed  of  three  kinds  of  substances, 
namely,  solids,  fluids,  and  spirits,  and  ultimately  resolvable  into 
the  four  primary  elements  of  earth,  water,  air,  and  fire,  the  pre- 
dominance of  each  of  which  in  particular  individuals  gave  rise 
to  the  prevaihng  temperaments,  characterised  by  the  peculiar 
combinations  of  the  four  qualities  of  dry,  moist,  cold,  and  hot. 
Hence  arose  his  doctrine  of  temperaments,  already  noticed 
(§  862).  The  anatomical  details  which  are  interspersed  through- 
out his  works  are  numerous,  but  do  not  exhibit  any  profound 
knowledge  of  the  subject,  besides  being  in  many  instances  incor- 
rect. The  confession  which  he  made  on  his  visit  to  Democritus 
shows  that  he  had  not  devoted  any  considerable  portion  of  his 
time  either  to  physiology  or  to  practical  anatomy.  It  is  very 
apparent,  indeed,  that  he  never  dissected  a  human  body ;  and 
much  could  not  be  learned  from  the  occasional  dissection  of 
brutes.  So  far  was  he  from  having  any  idea  of  the  real  nature 
of  the  circulation  of  the  blood,  which  some  have  done  him  the 
honour  to  suppose  he  had  discovered,  that  he  seems  to  have  iixi- 
agined  that  the  arteries  contained  air,  and  he  was  at  a  loss  to 
determine  whether  the  veins  took  their  origin  in  the  liver,  the 
heart,  or  the  brain.  He  includes  under  the  same  name  the  liga- 
ments, the  tendons,  and  the  nerves,  and  makes  no  distinction 
between  their  respective  offices  in  the  economy.  But  these 
imperfections  were  more  to  be  imputed  to  the  unavoidable  dis- 
advantages of  the  times,  than  to  his  own  deficiency  either  of 


442  HISTORY   OF    PHYSIOLOGY. 

industry  or  of  talent ;  for  wherever  he  had  opportunities  of  dis- 
playing these  qualities,  and  of  exerting  the  whole  force  of  his 
original  mind,  he  far  surpassed  all  his  cotemporaries.  Hippo- 
crates must  indeed  be  regarded  as  the  father  of  physiology,  as 
well  as  of  medicine ;  and  his  name  will  ever  be  cherished  by 
posterity,  as  one  of  the  most  illustrious  in  the  annals  of  science. 

1130.  Amongst  the  Athenian  philosophers  who  paid  attention 
to  physiology,  Socrates  must  not  be  passed  over  in  silence ;  since 
he  cultivated  the  science  with  a  view  to  establish  upon  it,  as 
upon  the  most  solid  foundation,  the  principles  of  natural  theology. 
Plato,  the  friend  and  pupil  of  Socrates,  hkewise  devoted  a  por- 
tion of  his  time  to  the  study  of  animal  structures,  and  indulged 
in  a  variety  of  fanciful  speculations  concerning  the  uses  and  func- 
tions of  the  vital  organs. 

1131.  Aristotle,  the  tutor  of  Alexander  the  Great,  whose  trans- 
cendant  genius  embraced  the  whole  domain  of  human  science, 
prosecuted  this,  as  well  as  every  other  branch  of  the  history  of 
nature,  with  an  ardour  and  perseverance  that  have  rarely  been 
equalled,  and  never  surpassed.  Gifted  with  a  mind  of  extraor- 
dinary acuteness  and  comprehension,  he  appears  to  have  con- 
centrated within  it  all  the  learning  of  his  age,  which,  moulded  and 
transformed  by  the  power  of  his  genius,  assumed  new  forms  of 
arrangement,  yielded  new  products  of  generalization,  and  spread 
its  luminous  irradiation  over  every  department  of  human  know- 
ledge. At  the  request  of  his  pupil  he  undertook  an  extensive 
treatise  on  the  natural  history  of  animals  ;  he  was  liberally  fur- 
nished with  specimens  of  all  kinds,  and  empowered  to  command 
the  services  of  numerous  assistants,  from  every  part  of  the  vast 
empire  of  Alexander.  He  spared  no  labour  in  the  prosecution 
of  this  undertaking,  and  in  making  the  most  profitable  use  of  the 
resources  thus  placed  at  his  disposal ;  and  contributed  in  no  small 
degree  to  the  advancement  of  our  knowledge  of  the  animal 
economy  in  the  diversified  forms  of  life  presented  by  nature. 
Yet  with  all  the  advantages  he  possessed,  it  would  appear  that 
his  knowledge  of  human  anatomy  was  exceedingly  imperfect. 
He  even  acknowledges  that  the  internal  parts  of  the  human  body 
are  but  little  known  ;  and  points  out  the  probable  advantages  that 
might  result  from  the  examination  of  animals  which  have  the 
nearest  resemblance  to  the  human  species,  for  supplying  these  defi- 
ciencies. But  his  work  on  the  history  of  animals,  tt^i  ^rea,)/  urTopiac, 
is  unrivalled  by  the  magnitude  of  the  field  which  it  embraces,  and 
by  the  vast  information  it  contains.  To  him  belongs  the  merit 
of  arranging  the  facts  in  the  order,  not  of  their  zoological,  but 
their  physiological  relations  ;  referring  every  organ  to  the  func- 
tions it  performs  in  the  animal  economy,  and  thus  anticipating 
the  very  principle  on  which,  in  recent  times,  Hunter,  Blumen- 


HISTORY    OF    PHYSIOLOGY.  443 

bach,  and  Cuvier  have  founded  their  more  rational  and  philoso- 
phical views  of  comparative  physiology. 

1132.  The  encouragement  given  by  the  Ptolemies,  the  succes- 
sors of  Alexander  in  Egypt,  to  every  kind  of  learning,  tended 
greatly  to  the  advancement  of  anatomy  and  physiology.  Permis- 
sion was  granted  by  these  monarchs  to  dissect  the  human  body, 
which  none  would  otherwise  have  dared  to  attempt,  in  opposition 
to  the  prejudices  of  the  Egyptians,  which  were  no  less  violent 
against  dissection  than  those  of  the  Greeks. 

1 133.  One  of  the  earliest  of  the  physiologists  of  this  period  was 
Erasistratus,  the  grandson  of  Aristotle,  and  the  pupil  of  Chrysip- 
pus.  Under  the  patronage  of  Nicanor,  king  of  Sicily,  he  enjoyed 
frequent  permission  to  dissect  the  bodies  of  those  who  were  exe- 
cuted, and  is  even  reported  by  Celsus  to  have  had  criminals 
delivered  to  him  for  the  purpose  of  their  being  opened  while 
alive,  in  order  that  the  natural  living  state  of  the  internal  organs 
might  be  examined.  This  account,  however,  deserves  to  be  re- 
garded rather  as  a  popular  tale,  which  has  no  other  foundation 
than  irrational  prejudices  against  dissection,  and  was  propagated 
by  idle  credulity,  and  a  passion  for  exaggerated  scenes  of  horror. 
The  works  of  Erasistratus  are  now  lost ;  but  from  the  quotations 
of  later  authors,  he  appears  to  have  greatly  advanced  the  know- 
ledge of  the  structure  of  the  human  body,  more  especially  by 
pointing  out  the  circumstances  in  which  it  differs  from  that  of 
other  animals,  whose  anatomy  had  been  previously  studied  as 
making  the  nearest  approach  to  the  organization  of  man. 

1134.  Another  no  less  distinguished  anatomist  of  the  same 
period  was  Herophilus  of  Chalcedon,  who  also  flourished  at 
Alexandria.  He  was  the  disciple  of  Praxagoras,  and  was  con- 
sidered as  the  founder  of  the  medical  school  at  Alexandria.  He 
was  much  occupied  in  the  dissection  of  human  bodies,  and  directed 
his  attention  particularly  to  the  nervous  system.  One  of  the 
sinuses  of  the  brain,  which  he  is  said  to  have  more  particularly 
described,  bears  to  this  day  the  name  of  the  torcular  of  Hero- 
philus. He  is  stated  to  have  been  the  first  anatomist  who  taught 
osteology  from  the  human  skeleton.  He  distinguished  the  nerves 
from  tendons  and  ligaments,  with  which  they  had,  before  his 
time,  been  confounded.  He  also  paid  minute  attention  to  the 
varieties  of  the  pulse,  and  thus  laid  a  foundation  for  a  knowledge 
of  the  important  function  of  the  circulation. 

1135.  Few  physiologists  of  any  note  are  recorded  as  having 
flourished  from  the  time  of  Herophilus  to  that  of  Galen.  The 
nam.es  of  Lycus  of  Macedonia;  of  Marinus,  who  lived  in  the 
reign  of  Nero,  have  been  transmitted  to  us  as  the  author  of  some 
elaborate  treatises  on  the  muscles ;  and  also  of  Rufus  Ephesius, 
who  wrote  a  work  entitled  Onomasia,  which  was  considered  as 
the  best  system  of  anatomical  knowledge  extant  at  that  period. 


444  HISTORY   OF    PHYSIOLOGT. 

1136.  Galen,  the  most  celebrated  and  indeed  the  last  of  the 
physiologists  of  Greece,  was  born  at  Pergarpos,  in  Asia  Minor, 
about  131  years  before  the  Christian  era.  His  father  was  imbued 
with  the  love  of  letters,  and  was  anxious  that  his  son  should 
receive  the  benefit  of  a  learned  education,  which  the  early  pro- 
mise he  gave  of  superior  talents  showed  that  he  was  well  quali- 
fied to  turn  to  advantage.  He  was  placed  under  the  tuition  of  the 
best  philosophers  of  the  time,  and  studied  in  all  the  schools  with 
extraordinary  diligence.  His  father  died  long  before  he  could 
form  any  probable  anticipation  of  the  future  fame  of  his  son.  It 
was  two  years  after  this  event,  that  young  Galen,  who  was  now 
in  his  nineteenth  year,  first  turned  his  attention  to  medical  pur- 
suits, of  which  he  soon  became  passionately  fond.  As  Alexandria 
was  still  the  most  celebrated  school  of  medicine  in  the  world,  he 
travelled  thither  with  a  view  of  prosecuting  his  studies ;  in  order 
to  reap  every  advantage  which  foreign  countries  could  afford,  he 
visited  in  succession  different  parts  of  Asia  Minor  and  the  islands 
in  the  JEgean  Sea.  Anatomy  was  ever  his  favourite  pursuit ; 
but  being  debarred  from  the  advantage  of  examining  human 
bodies,  the  dissection  of  which  had  then  been  prohibited,  even  at 
Alexandria,  he  had  recourse  to  that  of  such  animals  as  were 
supposed  to  have  the  greatest  resemblance  in  their  structure  to 
man.  He  has  written  very  fully  on  every  part  of  anatomy ;  so 
that  his  works  may  be  considered  as  a  system,  exhibiting  every 
thing  which  was  known  on  the  subject  in  his  time.  He  was 
much  impressed  with  the  importance  of  anatomy  as  the  basis  of 
medicine  and  surgery,  and  enforces  his  opinion  with  singular 
acuteness  and  energy.  This  is  evinced  by  the  following  passage 
in  his  second  book  of  Academical  Administrations  : 

"  What  can  be  more  useful  in  wounds  which  are  received  in 
battle,  in  the  extraction  of  darts,  excision  of  bones,  the  reduction 
of  luxations,  the  opening  of  fistulse,  than  to  be  well  acquainted 
with  the  anatomy  of  the  limbs  ?  It  is  of  more  use  to  be  acquainted 
with  the  exterior  than  the  interior  parts  of  the  body,  as  the 
shoulders,  back,  breast,  the  ribs,  the  belly,  and  the  outward 
covering  of  the  neck  and  head ;  for  we  are  often  required  to  cut 
into  abscesses  and  sinuses.  In  the  excision  of  bones  it  is  necessary 
to  cut  and  dissect ;  and  if  we  do  not  know  where  the  artery,  vein^ 
or  nerve  may  be,  we  are  more  likely  to  be  the  cause  of  death 
than  of  health  to  the  patient." 

1137.  Galen  is  entitled  to  great  praise  for  having  applied 
himself  to  the  investigation  of  physiology  in  connexion  with 
anatomy;  so  little  had  hitherto  been  known  on  this  subject,  that 
we  cannot  be  surprised  at  the  mixture  of  error  which  his  works 
exhibit;  but  although  he  may  often  have  proceeded  on  false 
principles  and  fallacious  hypotheses,  yet  the  reasonings  themselves 
which  he  employs  are  always  clear  and  conclusive.     His  account 


HISTORY    OF    PHYSIOLOGY.  445 

of  the  uses  of  the  hand,  for  example,  is  remarkably  perspicuous 
and  correct.  He  succeeded  in  estabUshing  by  experiment  the 
fact  that  arteries  contain  blood,  and  thus  refuted  the  doctrines  of 
the  Alexandrian  school  that  they  are  merely  filled  with  air,  which 
they  serve  to  distribute  throughout  the  body.  It  is  interesting 
also  to  trace  the  eifect  whicTi  these  subjects  of  contemplation 
produced  on  Galen's  mind.  After  reviewing  the  structure  of  the 
hand  and  foot,  and  their  adaptation  to  their  respective  functions, 
he  breaks  out  into  the  following  apostrophe,  admirably  charac- 
teristic of  a  mind  imbued  with  the  genuine  spirit  of  piety  : 

"  I  esteem  myself  as  composing  a  solemn  hymn  to  the  author 
of  our  bodily  frame,  and  in  this  I  think  there  is  more  true  piety 
than  in  sacrificing  to  him  hecatombs  of  oxen,  or  burnt-oflTerings 
of  the  most  costly  perfumes ;  for  I  first  endeavour  to  knov/  him 
myself,  and  afterwards  to  show  him  to  others,  to  inform  them 
how  great  is  his  wisdom,  his  virtue,  his  goodness." 

1138.  The  great  reputation  which  Galen  had  acquired,  instead 
of  promoting,  tended  rather  to  impede  the  progress  of  anatomy 
and  physiology  during  several  succeeding  centuries.  Where  no 
hope  was  entertained  of  emulating  the  fame  of  one  who  was  re- 
garded as  an  infallible  oracle,  all  motive  to  exertion  was  repressed. 
But  other  causes  of  a  political  nature  also  contributed  to  the 
decline  of  anatomy,  as  well  as  of  other  branches  of  learning,  from 
the  time  of  Galen  to  the  downfall  of  the  Roman  empire,  and 
during  the  ages  of  intellectual  darkness  which  followed.  Learning, 
however,  still  continued  to  be  cultivated  at  Alexandria,  until  the 
capture  of  that  city  by  the  Saracens,  in  the  year  640,  when  its 
magnificent  library  was  burnt. 

1139.  Anatomy  and  physiology  began  slowly  to  revive  among 
the  Arabians  ;  but  no  addition  seems  to  have  been  made  by  them 
to  the  knowledge  which  the  Greeks  had  possessed  on  these  sub- 
jects. The  Arabian  physicians  were  satisfied  with  what  Galen 
had  taught  them  ;  and  as  the  rites  of  the  Mahometan  religion 
prohibited  all  contact  with  a  dead  body,  an  effectual  bar  was 
opposed  to  all  improvement  in  anatomical  or  physiological  know- 
ledge. The  work  of  Avicenna  on  anatomy  is  merely  a  compi- 
lation from  Galen  and  other  Greek  authors ;  and  whenever  he 
ventures  to  differ  from  his  authorities  he  is  generally  wrong. 
For  more  than  a  thousand  years  after  the  time  of  Galen,  anato- 
mical and  physiological  science  may  be  considered  as  nearly 
stationary;  for  scarcely  any  discovery  of  the  least  importance 
was  made  during  the  whole  of  that  period. 

1140.  The  expeditions  of  the  crusaders  were  the  means  of 
introducing  into  Europe  some  knowledge  of  the  literature  of  the 
Arabians  ;  and  the  light  of  science,  after  a.  long  period  of  dark- 
ness and  ignorance,  began  at  length  to  dawn.  In  the  fourteenth 
century,  anatomy  was  revived  by  Mundinus,  a  Milanese,  who 

38 


446 


HISTORY   OF    PHYSIOLOGY. 


had  become  acquainted  with  the  writings  of  Galen  through  an 
Arabian  translation,  and  who  published  a  system  of  anatomy  in 
1315. 

1141.  The  destruction  of  the  Greek  empire  by  the  Turks,  in 
the  succeeding  century,  tended  to  diffuse  throughout  the  west  of 
Europe,  whatever  portion  had  remained  of  the  literature  of  the 
east.  The  learned  of  every  profession  fled  from  Constantinople, 
which  had  fallen  into  the  hands  of  barbarians,  and  sought  an 
asylum  in  Italy,  where  they  disseminated  the  seeds  of  knowledge. 
The  writings' of  Galen  and  of  the  ancients,  could  now  be  read  in 
the  original ;  their  superiority  to  the  Arabian  authors  was  soon 
discovered ;  and  such  implicit  deference  was  paid  to  their  opi- 
nions, that  for  many  ages  no  one  would  venture  upon  the  shghtest 
innovation.  The  improvement  of  anatomy  was  therefore  exceed- 
ingly slo4%  It  was  promoted,  however,  by  the  exertions  of 
eminent  painters,  such  as  Raphael,  Albert  Durer,  Titian,  and 
above  all,  Leonardo  da  Vinci,  whose  drawings  evince  consider- 
able knowledge  in  that  study. 

1 142.  The  sixteenth  century  was  more  auspicious  to  the  pro- 
gress of  anatomy,  which  was  beginning  to  be  cultivated  with 
ardour  in  Germany  and  France, ^as  well  as  in  Italy.  Berengarius 
of  Carpi,  professor  at  Bononia,  acquired  such  reputation  by  his 
skill  in  dissection,  that  he  was  regarded  as  the  restorer  of  this 
science.  The  structure  of  the  ligaments  and  bones  was  success- 
fully studied  by  Charles  Stephens ;  that  of  the  blood-vessels  by 
Fernelius  ;  and  that  of  the  muscles  by  Andernach.  Sylvius  was 
also  at  this  time  celebrated  as  a  teacher  of  anatomy. 

1143.  But  the  extravagant  veneration  of  antiquity,  that  spell 
which  has  for  so  many  ages  held  the  medical  world  in  thraldom, 
was  at  length  broken  by  Vesaiius,  who  boldly  ventured  to  call 
in  question  the  authority  of  Galen.  This  extraordinary  man  was 
born  at  Brussels  in  1514,  of  a  family  which  has  for  a  long  time 
cultivated  medicine.  He  united  to  remarkable  talents,  a  degree 
of  ardour  and  perseverance  which  enabled  him  to  overcome 
every  difRculty  ;  and  his  progress  in  the  study  of  anatomy,  for 
which  he  had  very  early  shown  a  partiality,  was  commensurate 
with  these  great  qualities.  He  commenced  his  studies  at  Lou- 
vain,  and  prosecuted  them  in  Italy.  In  a  short  time  he  made 
himself  master  of  the  Hebrew^  Greek,  and  Arabic  languages  ;  so 
that  before  he  had  attained  his  twentieth  year,  he  had  already 
read  the  works  of  Galen  and  Avicenna  in  the  original.  Such 
was  his  zeal  for  anatomy,  that  it  is  reported  he  used  to  rob  the 
gibbets,  and  dissect  the  bodies  in  his  bed-chamber.  In  a  few 
years  he  excelled  his  teachers,  Fernelius  and  Sylvius,  who  were 
esteemed  the  first  anatomists  of  their  time.  He  soon  detected 
many  errors  in  Galen,  some  of  whose  descriptions  of  parts  had 
been  taken  from  quadrupeds,  and  applied  to  man.     These  errors 


HISTORY   OF    PHYSIOLOGV.  447 

he  ventured  to  disclose  and  to  correct  in  his  publications ;  but 
his  boldness  in  appealing  to  nature  from  the  authority  of  Galen, 
drew  upon  him  the  enmity  of  all  the  admirers  of  that  great 
master.  He  was  assailed  from  all  quarters  with  the  bitterest  in- 
vectives ;  and  Sylvius  himself  has  not  scrupled,  in  the  heat  of  con- 
troversy, to  brand  him  with  the  epithet  of  Vesanus,  or  madman, 
in  allusion  to  his  real  name.  The  criticism  which  Vesalius  had 
passed  on  Galen,  was  retorted  by  his  enemies  upon  himself;  and 
it  must  be  confessed  that  in  the  plates  which  Vesalius  published, 
some  errors  of  the  same  kind  were  detected.  But  still  their 
general  accuracy  was  undeniable.  The  work  of  VesaUus  was 
soon  acknowledged  to  be  unrivalled,  and  its  author  eventually 
enjoyed  a  complete  triumph  over  all  his  opponents. 

His  fame  reached  the  eyes  of  Charles  V.,  who  appointed  him 
his  physician;  but  after  being  raised  to  that  distinguished  station, 
he  was  soon  doomed  to  experience  the  inconstancy  of  fortune. 
Having  obtained  permission/  to  examine  the  body  of  a  Spanish 
gentleman,  whom  he  had  attended  in  his  last  illness,  he  began  to 
lay  open  the  chest,  when  the  bystanders  imagined  they  perceived 
a  tremulous  motion  of  the  heart.  This  circumstance  soon  got 
wind,  and  probably  with  much  exaggeration,  reached  the  ears 
of  the  relations  of  the  deceased,  who,  seized  with  horror,  denounced 
Vesalius  as  a  murderer ;  and  coupling  this  charge  with  that  of 
impiety,  arraigned  him  at  the  tribunal  of  the  Inquisition.  Where 
superiority  of  knowledge  was  esteemed  a  crime,  Vesalius,  how- 
ever unjustly  he  might  be  accused,  was  certain  of  condemnation. 
By  the  influence,  however,  of  Philip  H.,  who  had  then  succeeded 
to  his  father  Charles  V.,  Vesalius  was  permitted  to  commute  his 
punishment  to  a  pilgrimage  to  the  Holy  Land,  the  merit  of  which, 
it  was  thought,  might  sufficiently  atone  for  the  heinousness  of 
any  crime.  This  journey  he  was  accordingly  obliged  to  perform ; 
and  on  his  return  he  was  invited  by  the  senate  of  Venice  to  teach 
anatomy,  but  he  perished  by  shipwreck  before  he  reached  that 
city,  when  he  was  about  fifty  years  of  age. 

1144.  The  impulse  which  had  been  given  by  Vesalius  to  the 
progress  of  anatomy,  continued  to  operate;  and  many  were  the 
inquirers  who  pressed  forward  in  the  path  in  which  he  had  so 
nobly  led  the  way.  The  barriers  to  investigation  had  been 
removed  ;  nature  was  open  to  inquiry ;  and  men  had  only  to 
observe  and  to  think  for  themselves.  Every  year  was  now 
adding  some  new  discovery  ;  and  it  becomes  no  longer  easy  to 
trace  the  order  of  their  succession,  or  to  ascribe  each  to  their 
proper  authors.  We  shall  endeavour,  however,  briefly  to  enume- 
rate those  which  are  most  worthy  of  being  noted. 

1145.  In  the  year  1561,  Fallopius  published,  in  Italy,  his 
Observationes  AnatomiccB,  a  work  of  much  merit,  and  the  fruit  of 
great  industry,     xlbout  the  same  period  also,  Eustachius  arrived 


448  HISTORY    OF    PHYSIOLOGY. 

at  great  eminence  as  an  anatomist,  and  published  a  set  of  plates 
which  he  himself  engraved  ;  their  beauty  and  accuracy  excite 
astonishment  even  in  the  present  day. 

1146.  Fabricius  ab  Aquapendente,  a  professor  of  anatomy  at 
Padua,  was  also  one  of  the  most  distinguished  anatomists  and 
physiologists  of  that  period.  He  published  a  splendid  volume  on 
the  formation  of  the  foetus,  and  bestowed  much  pains  in  investi- 
gating the  mechanism  of  the  motions  of  animals.  He  was  the 
first  who  delineated  and  drew  the  attention  of  the  public  to  the 
valves  of  the  veins,  which,  had  indeed,  been  imperfectly  seen  by 
Stephens,  Sylvius,  and  Vesalius,  and  the  existence  of  which  had 
been  denied  by  Fallopius  and  Eustachius.  It  was  this  discovery, 
perhapS;  more  than  any  other,  which  paved  the  way  for  that  of 
the  real  course  of  the  blood  in  its  circulation;  a  discovery  which 
was  reserved  for  the  illustrious  Harvey;  and  which  has  justly 
rendered  his  name  immortal.  As  it  may  be  interesting  to  review 
the  steps  which  led  to  this  important  physiological  discovery, 
we  shall  retrace  its  history  to  a  period  somewhat  more  remote. 

1147.  It  is  perfectly  well  ascertained,  from  an  examination  of 
the  works  of  Galen,  and  of  others  who  have  copied  from  him, 
that  the  ancients  had  not  the  most  distant  notion  of  the  real  nature 
of  the  circulation.  The  blood  was  believed  by  them  to  have  its 
origin  in  the  liver,  and  to  be  undulated  alternately  in  opposite 
directions  in  the  veins ;  they  imagined  that  the  finer  part  of  it 
transuded  through  the  septum,  or  partition  separating  the  cavi- 
ties of  the  heart,  from  the  right  to  the  left  side,  where  it  mingled 
with  the  air  received  into  the  lungs,  and  forming  a  vital  spirit, 
was  moved  by  a  sort  of  flux  and  reflux  along  the  arteries. 

1 148.  On  the  revival  of  anatomy  in  Europe  some  vague  notions 
of  the  pulmonary  circulation  appear  to  have  suggested  themselves 
to  many  eminent  men.  Vesalius  demonstrated  that  the  blood 
could  not  possibly  pass  from  the  right  to  the  left  ventricle  through 
the  septum  of  the  heart.  Realdus  Columbus,  who  was  professor 
of  anatomy  at  Padua,  and  had  been  a  pupil  of  Vesalius,  distinctly 
traced  the  passage  of  the  blood  through  the  vessels  of  the  lungs. 
The  same  fact  had,  however,  been  already  discovered  by  Michael 
Servetus,  who  was  born  in  Aragon  in  1509,  a,nd  who  is  more 
celebrated  as  a  theologian  than  as  a  physiologist.  Further  pro- 
gress was  made  by  Andrew  C^salpinus,  an  Italian  physician, 
who  speaks  of  a  communication  existing  between  the  veins  and 
arteries  at  their  remote  extremities,  and  notices  the  effect  of  the 
valves  of  the  arteries  and  of  the  auricles  as  calculated  to  prevent 
a  reflux  of  the  blood ;  but  he  is  quite  at  a  loss  to  reconcile  this 
observation  with  the  common  notions,  which  he  had  imbibed,  and 
to  which  he  still  adhered,  of  the  functions  of  these  vessels.  But 
notwithstanding  these  apparent  approximations  to  the  truth,  it  is 
probable  that  many  ages  would  have  elapsed  before  the  complete 


HISTORY    OF    PHYSIOLOGY.  449 

discovery  of  the  circulation,  if  some  bold  and  penetrating  genius, 
such  as  that  of  Harvey,  had  not  arisen. 

1149.  This  illustrious  man  was  born  in  the  year  1578;  and 
the  circumstances  of  his  family  gavp  him  the  advantage  of  a 
liberal  education.  After  six  years  spent  at  Cambridge,  where 
he  was  instructed  in  all  the  philosophy  of  the  times;  finding  that 
the  university  furnished  but  very  imperfect  means  of  studying 
either  anatomy  or  medicine,  he  repaired,  at  the  age  of  twenty- 
one,  to  Padua.  Here  he  became  the  pupil  of  Fabricius,  who 
was  at  the  time  demonstrating  to  his  students,  with  all  the 
enthusiasm  of  a  discoverer,  the  newly  observed  valvular  structure 
of  the  veins.  The  attention  of  Harv^ey  being  thus  directed  to 
this  remarkable  conformation,  he  became  anxious,  on  his  return 
to  England,  to  prosecute  the  inquiry  into  the  purposes  which  were 
accomplished  by  it.  He  was  obliged,  for  this  purpose,  to  make 
many  experiments  on  living  animals;  and  these  revealed  to  him 
the  real  course  of  the  blood  in  its  circulation;  a  discovery  which 
ranks  unquestionably  as  the  noblest  and  most  important  ever 
made  in  Physiology.  Harvey  taught  this  new  doctrine  in  his 
lectures  about  the  year  1616  ;  but  did  not  publish  any  account  of 
it  till  the  year  1628.  On  its  being  made  known  to  the  world,  it 
met  with  the  most  violent  opposition  ;  and  so  inveterate  were  the 
prejudices  of  the  public,  that  the  practice  of  Plarvey  was  con- 
siderably diminished  in  consequence  of  his  discovery.  It  was 
remarked  that  no  physician  who  had  passed  the  age  of  forty 
would  admit  the  truth  of  a  doctrine  so  much  at  variance  with  all 
the  systems  in  which  he  had  been  educated.  Envious  of  his 
growing  reputation,  many  of  his  cotemporaries  had  recourse  to 
all  kinds  of  sophistry  with  the  view  of  detracting  from  his  merit. 
They  at  first  vehemently  contested  the  truth  of  the  doctrine  ;  but 
afterwards,  when  forced  to  admit  it  by  the  decisive  evidence 
adduced  in  its  support,  they  changed  their  ground  of  attack,  and 
alleged  that  the  merit  of  the  discovery  did  not  belong  to  Harvey, 
the  circulation  having  been  known  even  to  the  ancients.  But 
vain  were  all  the  efforts  of  envy  and  detraction  to  lessen  that 
fame,  which  will  command  the  admiration  of  all  future  ages. 
The  physiological  researches  of  Harvey  were  not  confined  to  the 
function  of  circulation  ;  but  extended  also  to  that  of  generation, 
and  to  the  evolution  of  the  ovum,  on  which  he  made  a  series  of 
very  valuable  observations. 

11.50.  The  beginning  of  the  seventeenth  century  was  an  import- 
ant era  in  anatomy,  for  it  was  also  marked  by  another  brilliant 
discovery,  namely,  that  of  the  lacteals  by  Aselli  in  1622.  It 
appears,  from  the  testimony  of  Galen,  that  Erasistratus  had 
noticed  white  vessels  on  the  mesentery  of  kids;  but  the  observation 
was  not  followed  up,  and  these  vessels  were  supposed  to  have 
been  merely  veins.  Aselli  was  born  at  Cremona,  and  was  professor 

38* 


450  HISTORY   OF    PHYSIOLOGY. 

of  medicine  at  Pavia.  He  observed  on  the  mesentery  of  a  dog 
numerous  vessels,  filled  with  a  white  fluid  ;  he  was  immediately 
convinced  that  he  had  made  an  important  discovery,  and  uttered 
in  the  fulness  of  his  feelings,  the  exclamation  "  Et//i«za."  Perceiv- 
ing similar  vessels  upon  the  surface  of  the  liver,  and  entertaining 
spme  theoretical  views  concerning  the  functions  of  that  organ, 
he  too  hastily  concluded  that  the  lacleals  terminated  in  the  liver. 
Aselli.  published  an  account  of  his  discovery  With  coloured  prints 
in  16--^7. 

1151.  It  was  not  till  about  thirty  years  after  this  discovery  of 
Aselli,  that  the  lacteals  were  traced  by  Pecquet,  a  Ji'rench 
anatomist,  into  the  receptaculum  chyli,  and  thence  into  the  thoracic 
duct,  which  he  also  followed  to  its  termination  in  the  great  veins 
near  the  heart.  These  observations  were  published  in  the  year 
1651.  All  these  discoveries  were  made  in  brutes  ;  and  it  remained 
to  be  shown,  that  similar  structures  existed  in  man.  This  was 
accomplished  by  Veslingius,  w^ho  had  already  demonstrated  the 
human  lacteal  vessels,  in  the  year  1634;  and  the  human  thoracic 
duct  in  1649.  These  parts  were  afterwards  more  fully  investigated 
by  Peirish  and  Vanhorne.  Shortly  afterwards,  the  general  absor- 
bents of  the  body  were  discovered  by  Olaus  Rudbeck,  a  Swede, 
who  was  born  at  Avosa,  in  the  year  1630.  This  discovery  was 
also  claimed  by  Thomas  Bartholin,  who  was  born  at  Copenhagen 
in  the  year  1616:  but  by  his  own  account  he  had  not  seen  these 
lymphatic  vessels  till  December  1651,  whilst  Rudbeck  had  not 
only  observed  them,  but  had  distinguished  their  peculiarities  the 
year  before;  Rudbeck  had  also  traced  them  to  the  thoracic  duct, 
which  Bartholin  had  failed  to  do.  Dr.  Joliffe,  an  English  physician, 
has  also  contended  for  the  honour  of  this  discovery ;  but  from  a 
comparison  of  dates,  the  priority  is  clearly  in  favour  of  the 
Swedish  anatomist.  When  we  consider  the  minuteness  of  these 
vessels  and  the  transparency  of  their  coats,  we  are  able  to 
appreciate  the  difficulty  of  detecting  their  existence,  and  our 
surprise  must  cease  at  their  having  remained  unknown  for  so 
many  ages. 

1J52.  No  discovery  of  equal  importance  to  those  we  have 
mentioned  has  been  made  in  anatomy  since  that  period.  Many 
parts  of  the  body,  which  were  unknown  in  Harvey's  time,  have 
indeed  been  brought  to  light;  but  the  principal  improvement  has 
consisted  in  a  more  accurate  knowledge  of  the  composition  and 
minute  structure  of  the  several  organs.  For  this  we  are  chiefly 
indebted  to  the  invention  of  new  anatomical  processes,  both  of 
investigation  and  of  demonstration.  Two  principal  means  were 
employed  in  these  researches  ;  the  one  was  the  microscope,  the 
other  the  practice  of  injections. 

1153.  The  microscope  was  first  applied  to  the  purposes  of 
anatomical  inquiry  about  the  year  1661,  by  Malpighi,  who  was 


HISTORY    OF    PHYSIOLOGY.  451 

born  near  Bologna,  in  the  year  1638.  He  examined,  by  the  aid 
of  this  instrument,  the  minute  organization  of  all  the  vital  parts ; 
and  more  particularly  the  glands.  These  researches  into  the 
intimate  texture  of  various  parts  of  animals  were  prosecuted  with 
great  ardour  by  Leewenhoek,  a  Dutch  anatomist,  about  the 
year  1680.  In  explonng  this  new  field  of  inquiry,  which  opened 
views  so  remote  from  common  apprehension,  his  enthusiasm  has 
often  carried  him  beyond  what  was  real,  both  in  the  power  of 
the  instrument,  and  in  the  results  it  afforded.  But  still  much  has 
been  effected,  and  the  boundaries  of  the  science  have  been  greatly 
enlarged  by  the  skilful  employment  of  the  microscope. 

1154.  The  arts  of  preserving  the  parts  of  animals  when  dis- 
sected, by  drying  and  varnishing  them,  and  by  other  modes  of 
preparation,  had  long  been  practised  ;  and  in  these  Vanhorne  is 
said  to  have  attained  superior  excellence.  But  the  most  valuable 
invention  of  this  kind  was  that  of  injecting  into  the  vessels  cer- 
tain fluids  which  would,  after  a  time,  become  solid,  and  admit  of 
the  course  of  these  vessels  being  easily  traced.  The  injecting 
syringe  used  for  this  purpose  was  invented  by  De  Graaf,  a  Dutch 
anatomist,  about  the  middle  of  the  seventeenth  century  ;  and  soon 
after,  the  proper  materials  for  injection  were  discovered  by 
Swammerdam.  The  art  of  injection  was  carried  to  a  very  high 
degree  of  perfection  by  Ruysch ;  but  with  a  degree  of  selfish 
illiberality  which  cannot  be  too  strongly  condemned,  he  kept  secret 
the  methods  he  employed. 

1155.  The  advancement  of  Physiology  was  greatly  promoted 
both  by  the  practice  of  this  art,  and  by  the  dexterous  employment 
of  the  microscope  ;  and  discoveries  in  this  science  have  succeeded 
one  another  so  rapidlj^  from  the  period  of  their  invention,  that  in 
giving  an  account  of  them,  it  is  scarcely  possible  to  preserve  an 
unbroken  narration  ;  and  it  would  be  impossible,  in  this  sketch, 
to  I'ecount  the  numerous  minor  improvements  which  have  been 
made  in  our  knowledge  of  this  department  of  science  from  the 
epoch  down  to  which  we  have  now  brought  its  history.  Much 
error  was  still  mingled  with  the  acquisition  of  real  knowledge  on 
these  subjects  ;  and  it  has  required  the  exertion  of  the  more  severe 
and  scrutinizing  spirit  of  inquiry  which  characterizes  the  philoso- 
phers of  a  later  period,  to  winnow  the  grain  from  the  chafl',  and 
refine  the  pure  metal  from  the  superfluous  ore  which  had  been  dug 
up  along  with  it  from  the  mine.  Physiologists  were  slow  in 
recognising  the  peculiarities  which  appertain  to  the  vital  powers, 
and  those  of  the  beginning  of  the  eighteenth  century  long  persisted 
in  ascribing  the  phenomena  of  life  to  the  operation  of  the  same 
laws  which  regulate  those  of  inanimate  nature.  Hence  the 
history  of  physiology  is  occupied  at  that  period,  chiefly  by  the 
contentions  which  arose  between  the  rival  sects  of  chemists,  and 
mathematicians ;  each  striving  to  apply  to  physiology  the  princi- 


452  HISTORY    OF    PHYSIOLOGY. 

pies  and  methods  of  investigation  which  prevailed  in  their  respec- 
tive sciences.  Much  ingenuity  was  wasted  in  these  unprofitable 
researches  ;  for  although  some  important  fact  was  occasionally 
brought  to  light  by  the  prosecution  of  elaborate  inquiries,  prompted 
by  endeavours  to  support  each  favourite  speculation,  yet  not  one 
of  these  hypotheses  could  long  maintain  its  ground,  nor  could  it 
be  said  that  a  single  general  principle  had  been  established. 

1 1 56.  A  new  light  was  now  thrown  on  the  subject  of  physiology, 
which  tended  to  dissipate  the  clouds  of  error  in  which  it  had 
been  obscured  by  the  dogmatical  tenets  of  both  the  chemical  and 
the  mechanical  sects  ;  and  to  effect  a  complete  renovation  in  the 
science.  The  new  doctrine  which  thus  superseded  the  former, 
originated  in  Stahl ;  who,  although  educated  in  the  school  of  the 
chemists,  soon  shook  off  the  trammels  of  his  instructors,  and  with 
the  vigour  of  native  genius  began  to  reflect  for  himself.  He  per- 
ceived the  futility  of  their  doctrines,  and  strongly  impressed  with 
the  wide  differences  observable  between  the  phenomena  presented 
by  organized  beings,  and  those  which  the  same  bodies  exhibit 
when  devoid  of  vitality,  conceived  that  they  were  governed  by 
some  agency  opposed  to  the  ordinary  physical  powers  of  matter; 
and  to  this  agent  he  gave  the  name  of  anima  (see  §  101),  ascrib- 
ing to  it  endowments  allied  to  intelligence,  which  controlled  all 
the  changes  in  the  system,  and  of  which  the  operations  were 
alwa3^s  directed  to  salutary  ends.  This  hypothesis,  gratuitous 
and  unphilosophical  as  it  was,  had  the  beneficial  effect  of  direct- 
ing the  attention  of  physiologists  to  the  phenomena  which  pecu- 
liarly characterise  the  living  state,  and  prepared  them  for  the 
study  of  the  laws  of  these  vital  phenomena.  Much  praise  is  also 
due  to  Hoffmann,  who,  although  too  hasly  in  his  conclusions  to 
inspire  confidence  in  their  correctness,  appears  to  have  been 
amongst  the  earliest  of  the  followers  of  Stahl,  who  entertained 
proper  views  of  the  principles  and  objects  of  physiology.  Boer- 
haave  was  celebrated  at  this  time  for  the  extent  of  his  information, 
the  soundness  of  his  judgment,  and  his  talent  in  the  art  of  instruc- 
tion. His  doctrines  had  extensive  influence  in  the  schools  of 
medicine ;  but  being  destitute  of  the  solid  support  of  facts,  they 
did  not  long  survive  their  propounder. 

1157.  But  the  great  founder  of  modern  physiology  is  unques- 
tionably Haller,  whose  labours  in  this  field  of  inquiry  are  so  pro- 
digious in  extent,  and  so  fruitful  in  results,  that  the  publication  of 
his  Elements,  to  which  it  may  be  perceived  we  have  had  occa- 
sion in  the  course  of  this  treatise  perpetually  to  refer,  must  be 
considered  as  forming  an  important  era  in  the  history  of  the 
science. 

1158.  The  attention  of  physiologists  was  beginning  to  be  more 
particularly  directed  to  the  functions  of  the  nervous  system;  and 
the  labours  of  Whytt  at  this  period  had  tended  much  to  give  it 


HISTORY    OF    PHYSIOLOGY.  453 

this  impulse.  Amongst  the  host  of  names  which  claim  our  notice 
as  having  contributed  their  share  in  the  rapid  progress  of  disco- 
very, since  this  time,  we  can  point  out  only  a  few  of  the  most 
illustrious.  William  Hunter,  the  Monros,  and  CuUen,  are  amongst 
those  most  eminent  for  the  services  which  they  have  rendered  to 
physiology ;  but  perhaps  the  largest  contributor  to  the  mass  of 
facts  collected  in  modern  times  was  John  Hunter.  The  merits 
of  Bichat  v/ere  also  of  the  first  order ;  and  considering  how  early 
his  career  was  cut  short  by  the  hand  of  death,  the  additions 
which  he  has  made  to  the  stock  of  facts,  and  the  influence  which 
his  opinions  have  had  on  the  progress  of  the  science,  must  excite 
astonishment.  Germany  and  Italy,  as  well  as  France,  have  been 
prolific  in  ardent  devotees  and  successful  cultivators  of  physiology ; 
and  although  it  might  be  invidious  to  point  out  particular  names,  we 
should  be  sorry  to  omit  those  of  Spallanzani,  Blumenbach,  Som- 
merring,  Meckel,  Gmelin,  and  Miiller ;  nor  should  the  justly 
earned  fame  of  Cuvier  be  passed  over  in  silence,  even  in  this 
brief  and  imperfect  retrospect  of  the  benefactors  of  our  race,  for 
such  we  must  esteem  all  those  who  enlarge  the  sphere  of  human 
knowledge,  and  thereby  confer  the  most  solid  accession  to  the 
power  and  happiness  of  man. 


APPENDIX. 


ON    PH'RENOLOGY. 


Phrenology,  derived  from  p/i«v,  the  mind,  and  Koyog,  discourse,  is  a 
term  which  has  been  recently  applied  to  denote  a  new  doctrine  of 
mental  philosophy,  founded  on  a  presumed  knowledge  of  the  functions 
of  different  portions  of  the  brain,  obtained  by  comparing  their  relative 
forms  and  magnitudes  in  different  individuals,  with  the  propensities 
and  intellectual  powers  which  these  individuals  are  found  respectively 
to  possess.  This  term  has  of  late  years  totally  superseded  ihe  more 
unpretending  titles  of  Craniology  and  Cranioscopy,  by  which  this 
doctrine,  in  its  earlier  periods,  and  before  it  had  aspired  at  effecting  a 
revolution  in  psychology,  was  designated,  and  which  simply  implied 
the  study  of  the  external  forms  of  the  skull,  both  in  men  and  animals, 
with  a  view  to  determine  the  size  of  the  subjacent  parts  of  the  brain, 
and  thence  to  derive  indications  as  to  the  mental  and  moral  qualities  of 
each  individual. 

'  The  original  propounder  of  the  doctrine  which  is  the  basis  of 
phrenology  was  Dr.  Gall,  a  physician  of  Vienna,  whose  system,  ma- 
tured in  conjunction  with  Dr.  Spurzheim,  has  attracted  so  much  at- 
tention, and  been  so  keenly  discussed,  both  here  and  on  the  continent, 
that  we  think  it  our  duty  to  present  our  readers  with  a  general  outline 
of  this  pretended  science. 

Of  the  several  parts  which  compose  the  human  body,  the  mechanism 
of  which  has  been  so  thoroughly  unfolded  by  the  diligence  of  modern 
anatomists,  there  are  few  wiiose  use  in  the  economy  is  wholly  un- 
known. The  intention  and  operation  of  every  part  of  our  frame  sub- 
servient to  the  mechanical  purposes  of  connexion,  of  locomotion,  and 
of  strength,  such  as  the  bones,  muscles,  and  ligaments,  are,  in  general. 
Sufficiently  apparent;  the  functions  performed  by  the  abdominal  and 
thoracic  viscera  are,  for  the  most  part,  well  ascertained  ;  and  we  are 
able,  in  like  manner,  to  discern  the  adaptation  of  the  organs  of  sense 
to  receive  appropriate  impressions  from  surrounding  objects.  One 
organ  alone,  and  an  organ  of  vast  importance  in  the  system,  connected 
"with  every  other,  and  essentially  interwoven  with  our  sensitive  exist- 
ence, has  baffled  all  investigation,  and  still  presents  a  wide  blank  in 
this  rich  and  cultivated  field  of  knowledge.  The  brain,  that  large  mass 
of  pulpy  substance,  which  fills  the  cavity  of  the  cranium,  is,  even  at 


456     '  APPENDIX. PHRENOLOGY. 

the  present  day,  as  incomprehensible  in  its  functions,  as  it  is  subtle 
and  complex  in  its  anatomy.  It  appears,  indeed,  to  be  sufficiently 
established,  that  the  brain  is,  in  some  unknown  way,  subservient  to 
sensation  and  voluntary  motion,  and  is  thereby  the  immediate  agent 
by  which  the  soul  and  body  mutually  exert  an  influence  over  each 
other:  and  it  has  also  been  very  generally  supposed,  that  this  organ 
is  immediately  concerned  in  all  our  mental  operations,  besides  being 
the  instrument  by  which  we  feel  and  act.  But  the  phenomena  com- 
prehended under  the  operations  of  the  mind  are  exceedingly  various 
and  complicated,  and  are  also  of  very  different  kinds  ;  so  that  before 
we  can  reason  concerning  them,  it  is  necessary  that  they  should  be 
properly  distinguished  and  arranged.  Metaphysicians  have,  accord- 
ingly, classed  them  as  referable  to  our  sentient,  our  intellectual,  our 
active,  and  our  moral  powers.  Further  subdivision  again  is  required ; 
and  the  intellectual  phenomena,  for  instance,  are  arranged  according  as 
they  relate  to  the  faculties  of  conception,  association,  memory,  abstrac- 
tion, judgment,  imagination,  invention,  &c.  Other  phenomena  are  distri- 
buted under  the  heads  of  the  different  active  principles,  such  as  the  propen- 
sities, the  instincts,  the  afiections,  and  the  passions,  which  belong  to  our 
nature.  Whilst  we  thus  discover  a  great  diversity  in  the  functions  of 
the  mind,  we  observe  also  as  great  a  complexity  of  structure  in  the  organs 
by  which  they  are  performed.  Shall  we  rest  satisfied  with  an  acqui- 
escence in  the  general  proposition,  that  the  brain  is  the  organ  of  thought? 
May  we  not  rather  regard  it  as  a  congeries  of  distinct  organs,  corre- 
sponding to  the  different  faculties  into  which  the  mind  may  be  analysed  ; 
each  organ  having  its  appropriate  office,  and  being  immediately  subser- 
vient to  some  particular  function  of  the  mind  ?  The  question  has, 
indeed,  presented  itself  to  many  physiologists  ;  but  few  have  ventured 
farther  in  attempting  its  solution,  than  to  thi-ow  out  some  vague  and 
general  conjectures  as  to  the  uses  of  certain  parts,  or  as  to  the  supposed 
habitation  of  the  sentient  principle.  Thus,  for  a  long  period,  it  was 
held,  that  the  cerebrum  was  the  organ  of  perception,  and  the  cerebellum 
the  organ  of  memory.  The  cavities  which  are  met  with  in  the  interior 
of  the  brain  have  often  been  considered  as  the  scene  of  the  intellectual 
operations.  Nemesius,  the  flrst  bishop  of  Emesa,  under  the  reign  of 
Theodosius,  taught  that  the  sensations  had  their  seat  in  the  anterior 
ventricles,  memory  in  the  middle,  and  understanding  in  the  posterior  ■ 
ventricles.  Albertus  Magnus,  in  the  thirteenth  century,  went  so  far 
as  actually  to  delineate  upon  a  head  the  supposed  seat  of  the  different 
faculties  of  the  mind.  He  placed  common  sense  in  the  forehead,  or  in 
the  first  ventricle  of  the  brain,  cogitation  and  judgment  in  the  second, 
memory  and  moving  power  in  the  third.  Peter  de  Montagnana,  in 
1491,  published  the  figure  of  a  head,  on  which  were  indicated  the  seat 
of  the  sensus  communis,  the  cellula  imaginaiiva,  cellula  sestimativa 
sell  cogitativa,  cellula  memorativa,  and  cellula  rationalis.  Ludovico 
Dolci,  Servito,  and  a  great  number  of  other  writers,  have  hazarded 
similar  hypotheses  as  to  the  locality  of  the  different  faculties.  Both 
Haller  and  Van  Swieten  fancied  that  the  internal  senses  occupy  differ- 
ent places  in  the  brain  ;  but  they  considered  its  whole  organization  as 
too  complicated,  too  intricate,  and  too  difficult,  to  allow  of  any  hope 


DR.  gall's  speculations.  457 

that  the  seat  of  memory,  of  judgment,  or  of  imagination,  could  ever  be 
detected." 

In  the  pursuit  of  this  speculation,  no  one  has  engaged  with  more 
ardour  and  perseverance  than  Dr.  Gall,  who,  after  many  years  of  patient 
labour,  and  much  fruitless  wandering  in  searcli  of  the  truth,  conceived 
that  he  had  at  last  discovered  the  clue  which  was  to  conduct  us  through 
the  mazes  of  this  labyrinth,  and  enable  us  to  arrive  at  a  more  accurate 
knowledge  of  human  nature,  and  of  the  means  which  may  conduce  to 
its  perfection.  The  account  which  he  gave  of  the  circumstances  that 
gradually  drew  his  attention  to  the  subject,  and  of  his  progress  in  this 
new  path  of  discovery,  is  as  follows  :  Brought  up  in  the  midst  of  a 
numerous  family,  and  naturally  gifted  with  the  talent  for  observation, 
he  was  struck,  even  when  a  boy,  with  the  diversities  of  disposition  and 
of  character  amongst  his  brothers  and  sisters,  and  the  companions  with 
whom  he  was  educated.  He  remarked,  that  each  excelled  in  a  particular 
study,  or  was  distinguished  by  a  peculiar  turn  of  mind.  One  was  noted 
for  the  beauty  of  his  handwriting;  another  for  his  quickness  at  arith- 
metic ;  a  third  for  his  aptitude  in  learning  languages ;  a  fourth  for 
remembering  everything  that  he  read  in  history. '  This  diversity  was 
apparent  in  all  that  they  did  ;  thus  the  style  of  composition  of  the  one 
was  remarkable  for  its  flowing  and  elegant  periods  ;  of  another  for  its 
baldness  and  dryness  ;  of  a  third  for  its  condensation  and  vigour.  Many 
displayed  talents  for  arts  which  had  never  been  taught  them  ;  they 
excelled,  perhaps,  in  drawing,  or  in  the  execution  of  works  of  mechan- 
ism ;  some,  sought  for  amusement  in  noisy  sports,  others  preferred 
cultivating  their  gardens  ;  a  few  placed  their  chief  delight  in  rambling 
through  fields  and  forests,  and  in  collecting  birds,  insects,  and  flowers. 
One  was  of  a  social  and  afl^ectionate  disposition,  another  was  selfish 
and  reserved  ;  a  third  was  fickle,  and  not  to  be  depended  upon.  The 
great  facility  with  which  some  of  his  school-fellows  could  commit  their 
tasks  to  memory,  which  to  him  was  a  work  of  immense  labour,  although 
in  matters  of  reasoning  and  judgment  he  felt  "himself  their  superior, 
often  proved  a  grievous  source  of  mortification,  and  excited  in  him  a 
strong  desire  to  know  the  cause  of  this  difference.  He  at  length 
remarked,  that  all  the  boys  gifted  with  this  kind  of  memory  had  large 
and  prominent  eyes.  He  afterwards  went  to  the  university  ;  and 
directing  his  attention  to  all  those  among  his  fellow-students,  who 
presented  the  same  peculiarity  of  feature,  he  learned  that  they  were  all 
distinguished  by  the  tenacity  of  their  memories;  as,  indeed,  he  soon 
found  to  his  cost,  for  ihey  were  sure  to  leave  him  far  behind  in  every 
competition,  where  the  exercise  of  this  faculty  was  essential  to  success. 
This  observation  gave  rise  to  others  ;  it  suggested  the  notion,  that  other 
intellectual  endowments  might  also  be  indicated  by  the  features  ;  and 
Gall,  by  degrees,  came  to  imagine  that  he  had  discovered  a  number  of 
external  signs,  which  respectively  indicated  a  decided  turn  for  painting, 
for  music,  for  mechanical  arts,  or  other  objects.  He  had  by  this  time 
commenced  the  study  of  medicine  ;  and,  in  the  course  of  his  academical 
instructions,  he  heard  much  about  the  functions  of  the  muscles  and 
viscera ;  but  nothing  was  taught  about  those  of  the  brain  and  its  different 
parts.     It  then  occurred  to  him,  that  the  differences   he  had  already 

39 


458  APPENDIX. PHRENOLOGY. 

noticed  in  the  external  configuration  of  the  head,  as  connected  with 
certain  dispositions  of  mind,  were  occasioned  by  differences  in  the  form 
of  the  brain.  Delighted  with  the  prospect  which  this  idea  opened  to 
him  of  discovering  the  functions  of  particular  parts  of  this  organ,  and 
of  obtaining  an  insight  into  the  connexion  between  the  mind  and  the 
body,  he  formed  the  resolution  of  prosecuting  the  research,  till  he  had 
either  accomplished  his  object,  or  satisfied  himself  that  it  was  not  to  be 
attained  by  that  method.  Natural  history,  which  had  long  been  his 
favourite  study,  furnished  ample  scope  for  the  extension  of  these 
inquiries.  He  had  been  in  the  practice  of  collecting  plants  and  animals- 
of  various  kinds,  and  of  arranging  them,  not  according  to  the  artificial 
methods  of  classification  detailed  in  books  of  science,  but  according 
to  their  more  obvious  resemblances.  He  now  studied  the  relations 
between  their  external  forms,  and  their  natural  habits  and  dispositions. 
Dogs,  showed  him  the  greatest  diversities  in  their  capabilities  of  being 
educated.  He  remarked  that  some  were  naturally  expert  at  the  chace, 
while  others,  of  the  same  breed,  could  not  be  trained  without  the  utmost 
difficulty ;  that  some  perpetually  lost  themselves,  while  others  found 
their  way  home  from  great  distances.  In  birds,  he  observed  that  one 
would  listen  with  attention  to  a  tune  which  it  heard,  and  immediately 
learn  it ;  while  another  of  the  very  same  brood  would  sing  nothing  but 
the  note  that  was  natural  to  it.  Whence,  he  would  ask  himself,  can 
arise  this  wide  diversity  among  individuals  ? 

The  solution  of  this  difficult  question  was  not  to  be  hoped  for,  unless 
by  means  of  observations  conducted  on  the  largest  possible  scale.  He 
therefore  set  about  examining  all  the  skulls  he  could  lay  hold  of,  that 
had  belonged  to  individuals  whose  history  was  known.  He  looked 
out  for  all  persons  in  any  way  distinguished  for  a  particular  talent  or 
moral  quality.  He  examined  their  heads  with  great  attention,  and 
noted  the  peculiarities  in  their  shape.  He  also  collected  observations 
on  other  individuals,  who  were  remarkable  for  the  weakness  of  any 
faculty,  and  then  compared  together  the  positive  and  negative  indica- 
tions. On  the  other  hand,  when  he  chanced  to  meet  with  a  head  that 
presented  some  singularity  in  shape,  he  was  at  much  pains  to  obtain 
information  as  to  the  moral  and  intellectual  character  of  the  person  to 
whom  it  belonged.  When  he  had  no  other  resource,  he  did  not  scruple, 
as  Dr.  Spurzheim  informs  us,  to  address  his  questions  directly  to  the 
person  in  whose  head  he  observed  any  distinct  protuberance.  We  are 
also  told,  that  he  was  in  the  habit  of  collecting  around  him  the  boys  he 
met  with  in  the  streets  of  Vienna,  and  of  inducing  them,  by  petty  bribes, 
to  confess  their  own  faults,  and  betray  those  of  their  companions.  He 
excited  them,  for  instance  to  fight  together,  in  order  to  discover  which 
possessed  most  courage,  and  thence  drew  inferences  as  to  the  organ 
which  prompted  that  sentiment.  In  order  to  obtain  more  precise  data 
for  his  conclusions,  he  endeavoured  to  procure  models  of  the  more 
remarkable  heads  that  he  met  with,  and  generally  got  permission  from 
the  individuals  themselves  to  take  a  cast  of  their  heads  in  plaster  of 
Paris.  The  Count  of  8auran,  then  minister  of  police  at  Vienna,  gave 
him  material  assistance  in  effecting  these  objects ;  and  he  was  thus 
in  no  long  time  in  possession  of  a  very  large  collection  of  casts,  all 
bearing  more  or  less  upon  the  several  points  of  his  theory.     If  he  hap- 


DR.    GALL  S    RESEARCHES.  459 

pened  to  hear  of  the  death  of  any  one  whose  head  he  had  already- 
moulded,  he  was  at  great  pahis  to  procure  his  skull,  that  he  might 
compare  the  form  of  its  different  parts  with  the  shape  of  the  head 
during  life.  As  it  was  soon  known  that  the  doctor  aimed  chiefly  at 
those  who  possessed  some  remarkable  talent,  a  very  general  alarm 
spread  itself  amongst  the  inhabitants  of  Vienna;  and  not  a  few  were 
pursued  with  the  terror  of  being  selected  as  the  subjects  of  craniosco- 
pical  investigation,  and  of  their  skulls  being  destined  to  make  a  figure 
in  his  anatomical  cabinet.  The  aged  Mr.  Denis,  librarian  to  the  em- 
peror, is  said  to  have  inserted  an  express  clause  in  his  will,  to  protect 
his  head  from  the  keen  scalpel  of  Dr.  Gall.  Notwithstanding  these 
fears  and  precautions,  he  contrived  to  amass  an  extensive  collection  of 
skulls,  as  well  as  of  heads,  in  illustration  of  his  doctrines.  He  next 
availed  himself  of  the  aid  of  comparative  anatomy  ;  and  having  no  family 
to  provide  for,  spared  no  expense  in  procuring  skulls  of  all  sorts  of 
animals,  with  a  view  of  tracing  the  form  and  size  of  corresponding 
organs  throughout  the  whole  series.  Being  physician  to  the  establish- 
ment for  the  deaf  and  dumb  at  Vienna,  he  had  opportunities  of  observ- 
ing the  natural  features  of  uncultivated  minds,  and  the  various  degrees 
in  which  they  were  susceptible  of  education.  With  the  same  view, 
he  used  to  call  together  into  his  house  persons  of  the  lowest  class,  such 
as  coachmen,  and  beggars  in  the  street,  and  excite  them  to  display  their 
characters  before  him.  His  professional  practice  made  him  acquainted 
with  a  great  number  of  families,  and  afforded  him  many  opportunities 
of  making  valuable  observations.  He  neglected  no  means  of  instruction 
that  could  be  derived  from  the  inspection  of  the  heads  of  patients 
labouring  under  different  forms  of  insanity.  He  was  physician  to  the 
director  of  establishments  for  education,  and  was  allowed  to  examine 
every  child  who  excelled,  or  showed  any  remarkable  disposition.  He 
visited  the  prisons  and  houses  of  correction,  as  well  as  the  hospitals 
for  idiots  and  lunatics.  He  took  casts  of  the  heads  of  criminals,  in- 
quired into  the  offences  for  which  they  were  confined,  and  collected 
the  history  of  their  lives  ;  and  thus  derived  from  every  quarter  materials 
for  bringing  his  theory  to  perfection. 

As  his  observations  multiplied,  he  became  sensible  that  he  had 
fallen  into  many  errors  in  the  earlier  periods  of  his  inquiries,  and  was 
forced  to  give  up  many  of  his  favourite  opinions,  which  he  found  had 
been  too  hastily  adopted,  with  regard  to  the  general  form  of  the  head, 
as  connected  with  the  character  of  the  individual.  He  felt  the  neces- 
sity of  being  in  future  more  on  his  guard,  and  resolved  to  institute  a 
separate  examination  of  the  different  regions  of  the  skull ;  and  although 
he  was  here,  also,  frequently  obliged  to  shift  his  ground  in  assigning 
the  function  of  each  part,  his  researches  were,  on  the  whole,  attended 
with  more  uniform  success.  By  degrees  he  acquired  greater  confidence 
in  the  stability  of  his  conclusions,  and  at  length  ventured  to  announce 
them  to  the  public,  by  the  delivery  of  lectures  on  his  new  science. 
His  doctrines  were  eagerly  received,  and  much  canvassed  at  Vienna; 
but  their  fame  had  no  sooner  reached  the  Austrian  court,  than  a  violent 
outcry  was  raised  against  them  by  the  bigoted  priests,  who  controlled 
all  the  operations  of  that  weak  and  misguided  government,  and  who 


460  APPEN^DIX. PHRENOLOGY. 

represented  these  doctrines  as  tending  to  materialism  and  atheism.  The 
consequence  of  this  senseless  clamour  was,  that  Gall  was  interdicted 
from  lecturing.  But  the  number  of  those  to  whom  he  had  communi- 
cated the  principles  of  his  art,  and  in  whom  he  had  infused  a  strong 
desire  to  continue  to  profit  by  his  instructions,  was  by  this  time  very 
considerable,  especially  among  the  strangers  who  happened  to  be  at 
Vienna.  They  formed  a  strong  party  in  his  favour,  and  made  such 
interest  at  court,  principally  through  the  medium  of  the  foreign  ambas- 
sadors, that  the  doctor  was  again  permitted  to  resume  his  prelections, 
on  condition  that  he  delivered  them  to  foreigners  only  ;  as  it  was 
wisely  considered  that  their  being  exposed  to  the  dangers  of  know- 
ledge, would  not  be  of  any  material  consequence  to  the  state,  as  long 
as  care  was  taken  that  the  infection  did  not  spread  farther ;  the  em- 
peror kindly  preserving  the  bliss  of  ignorance  for  the  exclusive  enjoy- 
ment of  his  Austrian  subjects. 

It  was  long  before  Gall  committed  himself  by  writing  on  the  subject 
that  had  procured  him  so  much  celebrity.  He  merely  announced,  in 
1798,  in  a  letter  addressed  to  Baron  Retzer,  which  appeared  in  the 
Deutsche  Merkur  of  Wieland,  his  design  of  publishing  a  large  work 
on  the  new  theory,  of  which  he  affords  his  readers  only  an  imperfect 
glimpse.  A  detailed  account  was  afterwards  given  by  M.  Froreiss,  one 
of  his  pupils,  in  the  second  volume  of  Voight's  Magazin  Physique; 
and  an  amusing  outline  appeared  from  the  pen  of  M.  Charles  ViUers,  in 
a  letter  addressed  to  Cuvier.  *  Various  surreptitious  copies  of  his  lec- 
tures were  also  circulated  throughout  the  protestant  states  of  Germany, 
where  they  excited  so  much  curiosity,  that  Dr.  Gall  was  at  length 
induced  to  make  a  tour  for  the  purpose  of  delivering  them  himself  at 
the  principal  universities  in  the  north  of  Germany.  "With  this  view 
he  visited  Dresden,  Berlin,  Halle,  Jena,  Weimar,  Gottingen,  Ham- 
burgh, &c.  and  every  where  met  with  the  most  flattering  reception, 
being  invited  to  the  several  courts  of  the  states  through  which  he 
passed,  and  treated  with  the  honours  due  to  a  distinguished  literary 
character.  By  frequenting  the  first  societies,  and  conversing  with  the 
best  informed  persons,  he  had  ample  opportunities  of  extending  his 
observations,  and  he  was  attentive  to  improve  these  opportunities  to 
the  utmost  of  his  power.  Dr.  Spurzheim,  who  had  at  an  early  period 
been  associated  with  him  in  these  inquiries,  and  who  had  devoted 
himself  particularly  to  the  anatomical  researches  they  comprised,  ac- 
companied him  in  this  tour,  and  participated  in  all  his  labours.  Dr. 
Gall  at  length  settled  in  Paris,  where  he  continued  his  pursuits  and 
lectures,  and  united  with  them  the  practice  of  his  profession. 

In  1810  Drs.  Gall  and  Spurzheim  published,  in  conjunction,  the 
first  volume,  in  quarto,  of  the  work  they  had  announced,  and  which 
was  to  contain  a  full  account  of  their  doctrines,  under  the  title  of 
Anatomie  ct  Physiologie  du  systeme  nerveux  en  general,  et  dii 
cerve.au  en  pariiculier,  avec  des  observations  sur  la  possihiliie  de 
reconnoitre  plusieurs  dispositions  intellectu'elles  et  morales  Vhomme 
et  des  animaux,  par  la  configuration  de  leurs  tetes.  The  first  part  of 
the  second  volume  appeared  in  1812.  This  work,  together  with  the 
one  published  in  1815,  by  Dr.  Spurzheim,  entitled  The  Physiogno- 


MENTAL    FACULTIES   INNATE.  461 

mical  System  of  Drs.  Gall  and  Spur zheim,  founded  on  an  anatomical 
and  physiological  examination  of  the  nervous  system  in  general,  and 
of  the  brain  in  particular,  arid  indicating  the  dispositions  and  mani- 
festations of  the  mind,  contain  the  most  authentic  account  of  their 
system.  Information  on  the  subject  may,  however,  be  derived  from 
the  following  books,  besides  those  of  Froreiss  and  Villers,  already 
mentioned.  The  best  of  the  foreign  works  is  that  of  Professor  Bischoff, 
entitled  Darstellung  der  GaW  schen  Gehirnund  Schddellehre,  nebst 
Bemerkungen  uber  diese  Lehre,  von  D.  W.  Hufeland,  Berlin,  1805. 
At  Dresden,  in  1806,  Bloede  published  a  similar  work,  viz.  Galls 
Lehre  Uber  die  Verrichtungen  des  Gehirns,  nach  dessen  zu  Dresden 
gehaltenen  Vorlesungen ;  and  at  Paris,  in  the  same  year,  we  have, 
from  the  pen  of  Demangeon,  Physiologic  intellectuelle,  ou  develope- 
ment  de  la  doctrine  du  Professeur  Gall.  A  small  tract  in  English, 
entitled  Some  Account  of  Dr.  GalVs  new  Theory  of  Physiognomy, 
founded  upon  the  Anatomy  and  Physiology  of  the  Brain,  and  the 
Form  of  the  Skull,  appeared  in  London  in  1807,  and  is  chiefly  taken 
from  Dr.  Bischoff''s  work,  including  the  critical  strictures  of  Dr.  Hufe- 
land. Soon  after  the  publication  of  Dr.  Spurzheim's  book,  a  small 
volume,  principally  reprinted  from  a  short  tract  in  the  Pamphleteer, 
was  given  to  the  public  by  Mr.  Thomas  Forster,  under  the  title  of 
Sketch  of  the  New  Anatomy  and  Physiology  of  the  Brain  and  Ner- 
vous System  of  Drs.  Gall  and  Spurzheim,  considered  as  comprehend- 
ing a  complete  system  of  Zoonomy,  with  observations  on  its  tendency 
to  the  improvement  of  education,  of  punishment,  and  of  the  treatment 
of  insanity.  Two  pamphlets  in  opposition  to  these  doctrines  were 
published  by  Professor  Walton  of  Berlin,  in  1805,  of  which,  as  well 
as  of  BischofF's  work,  a  short  account  is  given  in  the  Edinburgh  Medi- 
cal and  Surgical  Journal  for  July  1806.  Dr.  Spurzheim  having 
conceived  that  he  was  unfairly  attacked  by  some  of  the  Reviews,  thought 
proper  to  publish  a  reply,  in  a  pamphlet  which  made  its  appearance  at 
Edinburgh,  in  1817,  entitled  Examination  of  the  Objections  made  in 
Britain  against  the  Doctrines  of  Gall  and  Spurzheim.  These, 
together  with  the  lectures  delivered  in  London  by  Dr.  Spurzheim,  are 
the  sources  which  have  supplied  the  materials  for  the  following  sum- 
mary. 

It  is  laid  down  both  by  Gall  and  Spurzheim  as  the  foundation  of  their 
doctrines,  that  the  nature  of  man,  like  that  of  all  other  created  beings, 
is  determinate,  and  that  the  faculties  with  which  he  is  endowed  are 
innate ;  that  is,  that  they  are  implanted  in  him  at  his  first  formation, 
and  are  not  the  result  merely  of  the  external  circumstances  in  which 
he  may  afterwards  happen  to  be  placed,  nor  of  the  wants  and  necessi- 
ties to  which  these  circumstances  may  have  given  rise.  They  warn 
us  that  this  opinion  is  by  no  means  at  variance  with  that  of  Locke, 
who  argues  against  the  innateness  of  ideas,  and  not  of  the  faculties  or 
capacities  of  receiving  ideas.  Education,  doubtless,  has  a  powerful 
influence  in  modifying  and  giving  certain  directions  to  these  faculties  ; 
but  the  faculties  themselves,  that  is,  the  capacities  of  feeling,  of  intel- 
lect, and  of  action,  must  have  already  pre-existed  before  they  could  be 
called  into  play,  and  thus  produce  the  various  phenomena  which  diversify 

39* 


462  APPENDIX. PHRENOLOGY. 

the  scene  of  human  life.  Savages  have  at  different  times  been  found  in 
woods  destitute  of  all  the  ordinary  faculties  of  rational  beings.  Their 
resemblance  to  brutes  has  been  supposed  to  be  the  consequence  of 
of  their  total  want  of  education;  but,  when  we  eome  to  examine  into 
their  real  condition,  we  shall  find  that  they  are  wretched  beings,  with 
great  bodily  defects  ;  for  the  most  part  deeply  tainted  with  scrofula, 
and  almost  always  complete  idiots.  In  general,  they  appear  to  have 
been  abandoned  in  their  childhood  by  their  parents,  to  whom  they  were 
burdensome.  The  pretended  savave  of  Aveyron,  who  was  kept  in 
the  Institution  for  the  Deaf  and  Dumb  at  Paris,  was  almost  completely 
idiotical.  He  was  quite  deaf,  and  his  head  atid  body  were  incessantly 
in  motion  from  side  to  side,  even  when  he  was  sitting. 

In  estimating  the  causes  of  that  diversity  which  we  see  prevailing 
in  the  characters  and  faculties  of  individuals,  much  has  been   ascribed 
to  the  influence  of  diet,  mode  of  living,  and  the  impressions  received 
in  early  infancy,  while  the  organs  are  yet  tender,  and  highly  suscepti- 
ble of  every  kind  of  external  influence.     But  the  operation  of  these 
causes,  as  well  as   the   power  of  education   in   general,  is   much   t^ 
limited  to  explain  the  immense  differences  we  observe  among  different 
men,  and  even  among  different  children  of  the  same  family.     Helvetius 
and  other  bold  metaphysicians   have  maintained  the   paradox,  that  all 
men  are  born   originally  the  same,  and  are   moulded   into  what  they 
afterwards    become   solely   by   the    force   of  external    circumstances. 
Genius,  according  to  this  doctrine,  is  a  mere  creature  of  the  fancy,  and 
originally  belongs  no   more  to   one   man  than  to   another.     Train  all 
men  alike,  and  their  powers,  their   attainments,  and  their  actions,  will 
all  be  similar.     Accident,  more  than  design  or  premeditation,  has  fixed 
the  destinies  of  great  men,  as  well  as  disposed  of  those  who  are  unknown 
to  fame.     "  Demosthenes,"  say  these  philosophers,  "  became  eloquent, 
because  he  heard  an  oration  of  Callistratus,  whose  eloquence  made  so 
deep  an  impression  on  his   mind,  that  he  aspired  only  to   acquire  this 
talent.     Vaucanson  excelled  in  mathematics,  because,  being    obliged, 
when  a  child,  to   stay  alone  in  the  waiting  room  of  his  mothers  con- 
fessor, he  found  there  a  clock,  examined  its  wheels,  and  endeavoured, 
with  the  help  of  a  bad  knife,  to   make  a  similar  machine   of  wood. 
He  succeeded  :    and  one  step  leading  on  to  another,  he  arrived  at  the 
construction   of  his  wonderful   automatons.     Milton  would   not  have 
composed  his  Paradise  Lost,  had  he  noi  been  deprived  of  his  place 
of  secretary  to  Cromwell.     Shakspeare  composed  his  tragedies  because 
he  was  an  actor,  and  he  became  an  actor   because  he  was   forced   to 
leave  his  native  place  on  account  of  some  juvenile  errors.     Corneille 
fell   in   love,  made  verses   for  the  object  of  his  passion,  and   thence 
became  a  great  poet.     An   apple  fell  from  a  tree  at  the  feet  of  Newton, 
while  he  was  in  a  contemplative  mood  :   this  event,  so  trivial   in  itself, 
led  him  to  the  theory  of  gravitation,"     Reflections  of  a  similar  kind 
are  often  met  with  in  the  writings  of  poets  and  moralists.     Those  con- 
tained in  Gray's  J^hgy  must  be  familiar  to  all  our  readers.     Dr.  John- 
son considered  talents  or  genius   as   a   tiling  that,  wiien  once  existing, 
might  be  directed  any  way.     Newton,  he  thought,  might  have  become 
a  Shakspeare,  for,  said  he,  a  man  who  can  run  fifty  miles  to  the  south, 
can  run  fifty  miles  to  the  north. 


FACULTIES   DEPENDENT    ON    THE    BRAIN.  463 

Yet  these  are  but  the  ingenious  speculations  of  the  theorist,  more 
calculated  to  dazzle  than  to  convince,  and  obviously  in  contradiction 
with  the  daily  experience  of  mankind.  Original  dilierences  in  the 
constitution  of  the  mind  exist  as  certainly  as  in  that  of  the  body  ;  and 
doubtless  are  dependent  upon  differences  in -organization.  Children 
often  show,  from  their  earliest  infancy,  the  germs  of  those  peculiarities 
of  character  which  adhere  to  them  through  life,  which  hardly  any 
education  can  alter,  and  which  no  condition  of  life  or  variation  of 
circumstances  can  afterwards  affect.  It  is  needless  to  expatiate  on  the 
subject  of  the  diversities  of  intellectual  powers  exhibited  by  different 
individuals  under  the  very  same  circumstances  of  birth  and  education  ; 
diversities  which,  as  we  have  already  seen,  first  directed  the  mind  of 
Dr.  Gall  to  his  physiognomical  researches.  Many  of  these  peculiarities 
are  unquestionably  derived  from  the  parent,  and  are  observed  to  prevail 
in  certain  families,  and  to  descend  througii  several  successive  generations. 

That  no  sensation,  or  other  affection  of  the  mind,  and  that  no 
operation  of  intellect  can  take  place  without  a  certain  condition  of  the 
nervous  system,  is  a  position  established  by  so  many  direct  proofs,  that 
its  truth  must  be  generally  admitted.  The  question  becomes  more 
difficult  when  we  come  to  inquire  what  pait  of  the  system  it  is  that 
exercises  these  functions.  It  is  quite  clear  that  the  sentient  principle 
does  not  reside  in  the  nerves,  or  in  the  part  which  receives  the  first 
impression  from  the  external  cause  of  sensation.  The  opinion  which 
has  been  embraced  by  many  physiologists,  and  particularly  Bichat, 
that  while  the  brain  is  the  organ  of  the  intellectual  faculties,  the  nerves 
of  the  great  viscera  of  the  abdomen  and  thorax  are  the  seat  of  the  moral 
sentiments,  is  at  variance  with  a  multitude  of  facts  in  comparative 
anatomy.  There  are  animals  endowed  with  the  faculties  ascribed  to 
these  nervous  plexuses,  or  ganglions  of  the  great  sympathetic  nerves, 
distributed  to  certain  viscera,  which  have  not  the  viscera  in  question. 
On  the  other  hand,  most  quadrupeds  have  viscera  analogous  in  their 
whole  structure  to  those  in  man,  without  having  the  faculties  of  which 
in  man  it  is  pretended  they  are  the  seat.  We  have  a  complete  series 
of  proofs  that  the  nerves,  of  then>«elves,  and  without  an  uninterrupted 
-continuity  with  the  brain,  can  produce  neither  sensation  nor  voluntary 
motion.  Compression  of  the  brain,  by  any  cause,  produces  an  entire 
suspension  of  all  sensation  and  consciousness,  and  puts  a  complete  stop 
to  every  operation  of  ihtellect.  All  the  other  parts  of  the  body,  on  the 
other  handi  may  be  wounded  or  destroyed,  and  even  the  nervous  mass 
of  the  spinal  marrow  may  be  compressed  or  injured,  at  a  certain  distance 
from  the  brain,  without  the  immediate  destruction  of  the  feelings  and 
intellectual  faculties.  In  tetanus,  produced  by  a  cause  remote  from  the 
brain,  the  other  nervous  systems  are  affected  in  the  most  violent  manner, 
while  the  functions  of  the  mind  continue  unimpaired. 

In  children.  Dr.  Spurzheim  observes,  the  brain  is  yet  pulpy,  and 
the  faculties  imperfect ;  its  growth  accompanies  their  improvement ; 
its  maturity  marks  their  greatest  degree  of  vigour.  If  its  development 
has  been  considerable,  the  manifestations  of  these  powers  are  energetic  ; 
if  small,  they  are  comparatively  weak.  In  proportion  as  the  organiza- 
tion of  the  brain  decreases,  the  strength  of  the  moral  sentiments  and 


464  APPENDIX. PHRENOLOGY. 

intellectual  faculties  decreases  also.  If  the  development  of  the  brain 
take  place  too  early  or  too  late,  the  faculties  exhibit  corresponding 
variations.  Certain  faculties  are  more  active  in  men,  and  others  in 
women,  according  to  the  difference  of  their  cerebral  organization  ;  and 
peculiarities  of  character  are  hereditary,  according  as  the  corresponding 
organization  of  the  brain,  on  which  they  depend,  is  propagated  from 
parents  to  their  children. 

Although  many  facts  show  that  considerable  injuries  may  be  sustained 
by  the  brain  without  detriment  to  the  mental  faculties,  yet  as  a  general 
principle,  it  is  contended  by  Dr.  Spurzheim,  that  these  faculties  are 
weakened  or  destroyed  in  proportion  as  the  brain  is  mechanically 
altered.  It  is,  however,  certain,  that  physiologists  are  by  no  means 
agreed  as  to  this  point;  and  that  innumerable  cases  might  be  quoted 
in  direct  contradiction  to  this  principle.  These  are  attempted  to  be 
explained  away  by  the  general  supposition,  that  most  of  them  are  the 
result  of  very  inaccurate  observations,  in  which  the  statement  of  the 
facts  has  been  distorted  and  vitiated  by  ignorance,  prejudice,  or  cre- 
dulity ;  and  that  the  rest  are  inconclusive  as  to  the  general  question, 
from  the  observers  not  being  aware  of  the  real  functions  of  the  injured 
parts,  and  being  inattentive  to  the  circumstance,  that  almost  all  the  parts 
of  the  brain  being  double,  the  loss  of  those  on  one  side  would  scarcely 
be  felt,  as  long  as  the  corresponding  organs  on  the  other  side  remained 
entire.  On  the  other  hand,  it  should  be  recollected,  that  a  derange- 
ment in  an  organ  may  occur  of  such  a  nature  as  that  our  senses  cannot 
enable  us  to  discover  it.  How  often  is  this  exemplified  in  fatal  dis- 
eases of  the  nervous  system,  such  as  hydrophobia,  tetanus,  and  atonic 
gout.  Analogy  shows  us  other  parts  where  apparently  no  proportion 
is  preserved  between  the  injury  and  the  derangement  of  function. 
Sometimes  large  abscesses  are -met  with  in  the  lungs  without  much 
disturbance  of  the  function  of  respiration  ;  and  ossification  of  the  heart, 
without  any  sensible  affection  of  the  circulation.  In  persons  possessed 
of  great  irritability,  very  slight  wounds  of  the  brain  may  produce 
serious  effects,  while  considerable  wounds  in  others,  who  are  less 
irritable,  shall  be  attended  with  no  bad  consequences.  This  consider- 
ation will  go  a  great  way  towards  explaining  the  fact,  that  in  many 
cases  of  insanity,  instead  of  our  discovering  any  change  in  the  brain,  a 
diseased  state  has  been  observed  in  the  liver,  the  bowels,  and  other 
viscera ;  and  may  serve  as  an  answer  to  the  assertions  and  objections 
of  Pinel,  who  states  that  the  most  accurate  dissections  have  not  taught 
us  any  thing  with  regard,  to  the  seat  of  mental  alienation,  and  that  we 
have  no  sufficient  data  to  conclude,  from  diseases  of  the  brain,  that  it 
is  exclusively  the  organ  of  the  intellectual  faculties. 

Those  who  have  opposed  the  theory  of  the  subserviency  of  the  brain 
to  the  operations  of  mind,  have  laid  great  stress  upon  an  argument 
derived  from  the  phenomena  of  hydrocephalus.  In  patients  afflicted 
with  this  disease,  the  brain  appears  to  be  destroyed  and  replaced  by 
water  ;  and  yet  the  intellectual  and  moral  faculties  have  remained 
perfect  to  the  last.  Drs.  Gall  and  Spurzheim  conceive,  that  the  facts 
have  been  very  erroneously  represented  ;  and  that  the  only  alteration 
which  the  brain  sustains  in  these  cases,  is  a  displacement  of  its  parts, 


OPINIONS    OF    PHYSIOLOGISTS. 


405 


and  not  an  absorption  of  its  substance.  The  effused  fluid,  by  accu- 
mulating in  the  ventricles,  gradually  unfolds  the  convolutions  of  the 
hemispheres  of  the  brain,  and  expands  them  to  such  a  degree,  that 
they  are  reduced  to  a  thin  stratum  of  substance,  constituting  a  sort 
of  bag,  within  which  the  fluid  is  still  contained.  This  stratum  of 
brain  is  sometimes  not  more  than  a  line  in  thickness,  and  is  generally 
lacerated  in  attempting  the  dissection ;  in  which  case  the  water  rushes 
out,  the  real  structure  escapes  notice,  and  the  fluid  is  erroneously 
supposed  to  have  been  accumulated  between  the  brain  and  its  mem- 
branes. 

It  has  been  advanced,  as  another  objection  to  the  same  theory,  that 
monsters  are  sometimes  born  without  any  brain,  who  yet  suck  and 
perform  various  movements.  Actions  of  this  kind,  however,  are  purely 
automatic,  and  appear  to  be  unattended  with  consciousness  ;  with  such 
actions  the  brain  has  no  concern  whatever.  Some  have  founded  their 
opposition  to  the  theory,  on  the  result  of  some  experiments  of  Duverney 
on  pigeons,  which,  it  is  alleged,  continued  to  perform  all  their  animal 
functions  after  the  whole  of  the  brain  had  been  removed  from  the  skull. 
But  Dr.  Spurzheim,  on  repeating  these  experiments  on  birds  and 
rabbits,  found,  indeed,  that  the  destruction  of  the  superior  parts  of  the 
brain  does  not  destroy  the  functions  of  the  five  senses  and  of  voluntary 
motion,  but  that  it  is  impossible  to  take  out  all  the  cerebral  mass  with- 
out killing  the  animal.  As  soon  as  the  corpora  striata  and  optic 
thalami  are  wounded,  convulsions  and  death  ensue  ;  consequently  he 
does  not  hesitate  to  pronounce  the  account  given  by  Duverney  to  be 
entirely  false.  He,  in  like  manner,  wholly  discredits  the  stories  related 
by  Morgagni,  Zacutus  Lusitanus,  Bartholine,  Haller,  Vallisneri, 
Moreschi,  Giro,  Dr.  Simson,  Sommerring,  and  others,  concerning 
petrified  or  ossified  brains  being  found  in  individuals,  without  prejudice 
to  the  exercise  of  their  intellectual  faculties.  He  admits  it  to  be 
doubtful,  how  far,  in  perfect  animals,  the  brain  may  be  necessary  to 
the  passive  consciousness  of  the  external  senses  ;  but  deems  it  certain, 
that  the  exertions  of  the  will,  including  voluntary  motion  and  reflection, 
depend  entirely  upon  the  brain ;  no  phenomenon  of  this  kind  ever 
taking  place  without  that  organ. 

Concluding,  therefore,  that  the  brain  is  the  organ  of  the  sensitive, 
the  intellectual,  and  the  moral  faculties,  we  have  next  to  inquire, 
whether  these  faculties  are  exercised  in  common  by  the  whole,  or  any 
particular  portion  of  the  brain,  or  whether,  on  the  other  hand,  they  are 
more  especially  the  offices  of  different  parts  of  that  organ.  Dr.  Gall 
adopts  the  latter  of  these  opinions,  ami  upon  this  view  of  the  subject  is 
the  whole  of  his  system  founded.  The  following  is  the  reasoning  on 
which  he  builds  it. 

Physiologists,  influenced  by  the  metaphysical  tenets  of  the  schools, 
have  often  maintained,  that  the  soul,  being  simple,  its  material  resi- 
dence must  be  simple  also,  and  that  all  the  nerves  must  end  at  one 
point ;  or,  which  amounts  to  the  same,  that  they  can  have  but  one 
common  origin,  because  each  individual  has  but  one  soul.  Bonnet, 
Haller,  and  others,  who  had  extended  its  seat  to  the  whole  substance 
of  the  brain,  were  opposed  by  these  metaphysicians,  who  did  not  re- 
flect that  a  little  more  or  less  room  could  not  enable  them  to  explain 


466  APPENDIX. PHRENOLOGY. 

any  better  the  nature  of  the  soul ;  nor  that,  as  Van  Swieten  and  Tiede- 
mann,  remark  a  material  point,  in  which  all  ideas  and  sensations  should 
centre,  is  inconceivable,  in  consequence  of  the  confusion  and  disorder 
that  would  result  from  such  an  arrangement.  It  appears  ridiculous, 
indeed,  that  the  physiologist,  to  whom  all  nature  is  open,  should  direct 
his  researches  and  inductions  by  the  guidance  of  such  frivolous  specu- 
lations. Great  pains  wers,  however,  taken  to  determine  this  central 
point,  or  sensorium  commune;  but  it  is  enough  to  enumerate  the  vari- 
ous and  contradictory  opinions  that  have  been  held  with  regard  to  it,  in 
order  to  be  satisfied  of  the  utter  futility  of  this  research.  Descartes,  in 
his  treatise  on  the  Passions,  labours  to  prove  that  the  soul  is  concen- 
trated in  the  pineal  gland.  This  hypothesis  continued  in  fashion  for 
some  time,  till  it  found  an  enemy  in  a  follower  of  Descartes,  the  Dutch 
physician  Boutekoe,  who  dislodged  the  soul  from  its  narrow  watch- 
tower  in  the  pineal  gland,  and  confined  it  in  the  more  spacious  prison 
of  the  corpus  callosum.  Lancisi,  Maria,  and  La  Peyronie,  successively 
declared  themselves  in  favour  of  this  new  opinion  ;  and  the  latter  of 
these  anatomists  wrote  a  memoir  in  support  of  it,  which  was  printed 
by  the  Academy  of  Sciences  in  1741,  and  which  has  since  been  repub- 
lished separately.  Digby  next  transferred  the  soul  to  the  septum  lucidum 
in  place  of  the  corpus  callosum.  Vieussens  allowed  it  greater  latitude, 
assigning  for  its  boundaries  those  of  the  centrum  ovale  of  the  medullary 
substance.  Willis,  again,  restricted  it  to  the  corpora  striata;  Serveto, 
to  the-  aqueduct  of  Sylvius.  Wharton  and  Schellhammer  placed  it  in 
the  commencement  of  the  spinal  marrow ;  Molinetti  and  Wrisberg  in 
the  pons  Varolii ;  Crusius  and  Meig  in  the  origin  of  the  medulla  oblon- 
gata ;  whilst  Drelincourt  and  others  lodged  it  altogether  in  the  cere- 
bellum. Lastly,  Sommerring  imagined  the  soul  to  reside  in  the  serosity 
which  moistens  the  inner  surface  of  the  ventricles,  to  which  he  had 
traced  the  extremities  of  many  nerves  from  the  organs  of  sense ;  and 
conceived  that  the  different  motions  or  oscillations  of  this  fluid  are  the 
immediate  material  cause  of  our  sensation. 

Discarding  the  notion  that  the  functions  of  sense  and  intellect  are 
concentrated  in  any  particular  point  or  portion  of  the  brain,  let  us 
next  examine  the  opinion  that  all  the  faculties  are  exercised  by  the 
whole  mass  of  brain  considered  as  one  organ.  We  may,  in  the  first 
place,  remark,  that  the  analogy  of  other  parts  of  the  system  is  adverse 
to  this  hypothesis.  Every  different  secretion  has  its  appropriate  gland, 
the  offices  of  which  are  never  interchanged.  The  liver  never  secretes 
urine,  nor  the  kidneys  bile.  The  five  external  senses  are  distinct  and 
independent  of  one  another.  Every  where  do  we  observe  that  nature, 
in  order  to  produce  various  effects,  has  varied  the  material  organs. 
The  structure  of  the  brain  in  its  different  parts,  is  far  from  being  simple 
and  uniform  ;  it  is  composed  of  two  substances  ;  the  one  soft,  pulpy, 
and  ash-coloured ;  the  other  white,  opaque,  and  fibrous  in  its  texture. 
The  fibres  of  the  latter  run  parallel  to  each  other,  having,  at  the  same 
time,  various  collateral  connexions,  but  by  no  means  uniting  in  any 
one  central  part  which  can  be  considered  as  their  common  origin  or 
termination.  The  parts  of  the  brain  are  numerous,  and  distinct  from  one 
another,  bearing  evidence  of  a  very  complex  and  artificial  construction. 


PLURALITY   OP   ORGANS.  467 

They  are  constant  in  their  general  arrangement  in  different  subjects, 
showing  in  this  respect  a  striking  contrast  with  the  distribution  of 
blood-vessels,  or  even  the  disposition  of  the  muscles  and  viscera,  in 
which  it  is  so  common  to  meet  with  variations.  Comparative,  as  well 
as  human  anatomy,  furnishes  strong  analogical  arguments  in  favour  of 
a  plurality  of  the  cerebral  organs,  corresponding  to  the  plurality  of 
faculties.  However  defective  may  be  our  knowledge  of  the  structure 
of  these  organs  in  the  lower  animals,  still  a  general  comparison  of  their 
faculties,  as  we  ascend  in  the  scale  of  being,  shows  us  that  the  number 
of  these  faculties  increases  in  proportion  as  the  cerebral  parts  are  mul- 
tiplied. The  immense  augmentation  of  the  powers  of  intellect  which 
we  behold  in  man,  when  compared  with  the  limited  instincts  of  ani- 
mals, is  neither  in  proportion  to  the  increased  size  of  the  five  external 
senses,  nor  of  any  other  part  of  the  body,  but  to  the  increase  of  the 
cerebral  organs  only.  It  is  the  great  size  of  the  hemispheres  of  the 
brain,  more  especially,  that  characterizes  this  organ  in  man,  and  esta- 
blishes superiority,  as  an  instrument  of  intellect,  over  that  of  all  other 
animals.  Man  unites  in  himself  all  the  organs  which  are  variously 
scattered  and  distributed  among  the  brute  creation ;  but  he  has  also 
organs  in  his  brain,  which  no  other  animal  besides  himself  possesses  ; 
and  these  are  the  seats  of  faculties  of  a  higher  order,  peculiar  to  him 
alone. 

Considerations  arising  from  the  differences  in  the  proportional  energy 
with  which  the  faculties  manifest  themselves  in  different  individuals, 
are  also  in  favour  of  the  plurality  and  independence  of  the  organs.  If 
the  brain  were  one  simple  organ  of  mind,  and  alike  instrumental  in  all 
its  faculties  and  operations,  wherever  we  meet  with  any  one  faculty  in 
a  state  of  high  energy,  we  must  suppose  the  whole  organ  adapted  to 
produce  this  degree  of  energy,  and  ought  to  expect  its  other  operations 
to  be  equally  energetic.  Yet  we  may  find  the  same  individual  remark- 
ably deficient  in  other  faculties,  which  are  equally  dependent  on  this 
organ.  One  person  shall  excel  in  verbal  memory,  while  he  cannot 
combine  two  ideas  philosophically  ;  another  is  a  great  painter,  but  a 
bad  musician,  or  a  wretched  poet ;  another  is  a  good  poet,  but  a  bad 
general.  If  the  brain  be  a  single  instrument,  it  cannot  be  at  once  both 
weak  and  strong;  it  cannot  exhibit  one  faculty  in  its  perfection,  and 
another  in  a  very  limited  extent.  But  all  difficulty  vanishes  if  we 
admit  it  to  be  an  assemblage  of  many  organs ;  for  the  combinations  of 
these  organs  may  be  as  infinitely  diversified  as  the  actions  and  powers 
of  man.  The  argument  derives  additional  force  from  the  readiness 
with  which  this  theory  may  be  applied  to  explain  the  diversity  of  cha- 
racter we  meet  with  in  the  brute  creation,  and  especially  to  the  varieties 
of  disposition  observable  among  some  of  our  domestic  animals,  which, 
under  the  same  circumstances  of  education,  exhibit  such  different 
qualities.  In  like  manner,  the  diversity  of  character  in  the  same  indi- 
vidual, at  different  periods  of  his  life,  are  most  readily  explicable  on 
the  supposition  of  distinct  organs,  which  have  their  respective  periods 
of  growth,  maturity,  and  decline.  The  analogy  of  the  external  senses 
is  also  strongly  in  favour  of  the  same  doctrine.  Thus  the  taste  and 
smell  appear  earlier  than  the  senses  of  seeing  and  hearing,  because 


468  APPENDIX. PHRENOLOGY. 

their  respective  organs  are  earlier  developed.  This  reasoning  will  be' 
confirmed  when  it  is  found,  as  will  afterwards  be  shown,  that  the  pro- 
portional size  of  the  different  parts  of  the  brain  is  very  different  in  dif- 
ferent individuals.  Is  it  not,  therefore,  reasonable  to  suppose,  that  the 
different  energies  of  the  several  functions  of  the  mind  are  connected 
with  these  differences  in  the  structure  of  the  organs  which  respectively 
produce  them  ? 

The  faculties  of  animal  life  are  incapable  of  long  continued  exertion ; 
rest  is  necessary  for  the  renovation  of  their  powers.  Fatigue  is  the 
consequence  of  the  prolonged  action  of  the  muscles  of  voluntary  mo- 
tion ;  but  when  one  set  of  muscles  are  fatigued,  the  power  of  others  is 
still  unimpaired,  and  they  are  ready  to  be  employed  in  a  different  ac- 
tion, without  any  additional  fatigue.  When  we  have  been  long  sitting, 
we  are  relieved  by  standing  ;  and  even  the  bed-ridden  find  ease  from  a 
change  of  posture.  Our  eyes,  in  like  manner,  may  be  fatigued  by 
looking  at  pictures ;  but  we  can  then  listen  to  music,  because  there  is 
one  organ  for  seeing,  and  another  for  hearing.  It  is  well  known  that 
study,  long  protracted,  produces  fatigue  ;  but  we  can  continue  to  study, 
provided  we  change  the  object  of  attention.  If  the  brain  were  a  single 
organ,  the  whole  of  which  is  employed  in  performing  all  the  functions 
of  mind,  a  new  foTm  of  study  should  increase  instead  of  relieving  the 
sense  of  fatigue.  Thus  the  analogy  is  complete  between  the  pheno- 
mena of  mental  and  bodily  exertion.  Are  we  not,  then,  justified  in 
extending  it  to  the  instruments  by  which  these  operations  of  mind  and 
body  are  effected  ? 

The  phenomena  of  sleep  are  also  readily  accounted  for  on  this 
hypothesis.  During  this  state  all  the  organs  do  not  remain  inactive  ; 
but  sometimes  a  particular  organ  enters  into  action,  and  this  constitutes 
dreaming.  The  state  of  vigilance  is  that  in  which  the  will  can  put  in 
action  the  organs  of  intellectual  faculties,  of  the  five  senses,  and  of 
voluntary  motion  ;  but  it  is  incorrect  to  define  it  as  the  state  in  which 
all  these  organs  are  active,  for  it  is  impossible  that  all  the  faculties 
should  be  active  at  the  same  moment.  Somnambulism  may  be  re- 
garded as  a  state  of  still  more  incomplete  sleep,  or  one  in  which 
several  organs  are  watching.  If,  during  sleep,  the  action  of  the  brain 
is  partial  and  is  propagated  to  the  muscles,  locomotion  takes  place  ;  if 
to  the  vocal  organs,  the  sleeping  person  speaks.  All  this  may  take 
place  in  different  degrees.  Some  persons  dream  and  speak  in  their 
sleep  ;  others  dream,  speak,  hear,  and  answer;  others,  besides  dream- 
ing, rise,  walk,  and  do  various  things.  This  latter  state  is  called 
somnambulism  ;  that  is,  the  state  of  walking  during  sleep.  Now  as 
the  ear  can  hear,  so  the  eyes  may  see,  while  the  other  organs  sleep ; 
and  thei-e  are  undoubted  facts  which  prove  that  several  persons  in  the 
state  of  somnambulism  have  seen  ;  but  it  has  always  been  with  the 
eyes  open.  There  are  also  convulsive  fits  in  which  the  patients  see 
without  hearing,  or  vice  versa.  Some  somnambulists  do  things  of 
which  they  are  not  capable  in  a  state  of  watching  ;  and  dreaming  per- 
sons reason  sometimes  better  than  they  do  when  awake.  This  phe- 
nomenon is  not  astonishing.  If  we  wish  to  reflect  upon  any  subject, 
we  avoid  noise,  and  all  external  impressions  ;  we  cover  the  eyes  with 


PLURALITY    OF    ORGANS.  469 

onr  hands,  and  we  put  to  rest  a  great  number  of  organs,  in  order  to 
concentrate  all  vital  power  in  one,  or  in  a  few.  In  the  state  of  dream- 
ing and  somnambulism  this  naturally  happens ;  consequently  the 
manifestations  of  the  active  organs  are  then  more  perfect  and  more 
energetic  ;  the  sensations  are  more  lively,  and  the  reflections  deeper 
than  in  a  state  of  watching. 

States  of  disease  are  also  adduced  as  proving  tlie  plurality  of  the 
cerebral  organs.  In  many  cases  of  insanity  we  find  only  one  faculty 
deranged,  whilst  all  the  rest  are  in  a  perfectly  sound  state.  Lunatics,  on 
the  other  hand,  are  met  with,  who  are  reasonable  only  while  pursuing 
some  particular  train  of  thought.  There  was  a  chemist,  for  instance, 
who  was  insane  on  every  subject  except  chemistry.  An  embroiderer, 
during  her  paroxysms  of  insanity,  while  uttering  the  greatest  absurdities, 
calculated  correctly  how  much  stuff  was  necessary  to  such  or  such  a  piece 
of  work.  The  effects  of  blows,  or  other  injuries  on  the  head,  supply 
facts  of  a  similar  kind,  which  afford  still  more  convincing  proofs  that 
the  brain  is  susceptible  of  being  very  partially  affected.  Some  per- 
sons lose  from  this  cause  the  memory  of  proper  names,  while  they 
preserve  the  memory  of  words  which  indicate  the  qualities  of  objects. 
One  Lereard  of  Marseilles,  after  having  received  a  blow  from  a  foil  in 
the  orbit,  lost  entirely  the  memory  of  names  ;  sometimes  did  not  recol- 
lect those  of  his  intimate  friends,  or  even  of  his  father.  Cuvier,  in  his 
historical  eulogium  on  Broussonet,  states  that  this  celebrated  botanist, 
after  having  recovered  from  an  apoplectic  fit,  never  could  recollect 
proper  names  nor  substantives,  though  he  had  recovered  his  prodi- 
gious memory  with  respect  to  other  objects.  He  knew  plants,  their 
figure,  leaves,  and  colovirs  ;  he  recollected  the  adjectives,  but  could 
never  recover  the  generic  substantives  by  which  they  were  designated. 
These,  and  similar  instances  of  partial  affections  of  the  faculties,  support 
the  supposition  of  their  being  owing  to  different  conditions  of  various 
parts  of  the  brain  subservient  to  these  faculties. 

Lastly,  the  doctrine  that  different  portions  of  the  brain  exercise 
different  mental  functions,  is  countenanced  by  numerous  authorities  in 
former  as  well  as  in  modern  times.  It  is  expressly  stated  in  the  writings  ' 
of  Boerhaave,  Van  Swieten,  Haller,  Prochaska,  Sommerring,  &c.  ; 
and  the  Academy  of  Dijon  long  ago  proposed  it  as  a  prize-question, 
to  determine  the  situation  of  these  different  cerebral  organs.  Charles 
Bonnet,  indeed,  went  the  length  of  maintaining  that  each  fibre  of  the 
brain  is  a  particular  organ  of  the  soul. 

It  seems  hardly  necessary  to  expose  the  absurdity  of  the  accusation 
that  these  doctrines  tend  particularly  to  materialism,  although  the 
dread  of  such  a  consequence  has  been  sanctioned  by  royal  edicts. 
There  are  two  opinions  only,  which,  in  respect  to  this  question,  stand 
opposed  to  each  other ;  namely,  that  which  asserts  perception  to  take 
place  by  the  intervention  of  a  material  organ,  and  that  which  asserts  it 
to  take  place  immediately  by  the  energies  of  the  mind  itself,  or  at 
least  without  the  intervention  of  the  body.  The  doctrines  of  Gall  are 
unquestionably  incompatible  with  this  last  opinion,  that  is,  with  pure 
immaterialism,  which  may  in  fact  be  regarded  as  denying  the  existence 
of  matter  altogether.     This  sceptical  spiritualism  can  be  avoided  only 

40 


470  APPENDIX. PHRENOLOGY. 

by  the  admission  of  the  necessity  of  a  material  organ ;  and  if  this  be 
admitted,  any  modification  of  such  opinion,  that  does  not  exclude  mind 
as  the  ultimate  percipient,  must  be  equally  remote  from  absolute 
materialism.  The  immalerialist  believes  that  it  is  the  soul  which  sees 
and  the  soul  which  hears,  as  much  as  that  it  is  the  soul  which  judges 
and  the  soul  which  imagines;  and  since  he  does  not  condemn,  as  im- 
pious, the  allotment  of  different  organs  of  sight  and  hearing,  what 
greater  heresy  is  there  in  the  allotment  of  different  parts  of  the 
sensorium,  as  the  organs  of  judgment  and  imagination?  If,  indeed, 
one  were  to  say,  that  the  affections  of  these  parts  are  themselves  judg- 
ment and  imagination,  he  would  be  a  materialist,  but  he  would  be  as 
much  a  materialist,  if  he  should  say,  that  the  affections  of  the  organs 
of  sight  and  hearing  are  themselves  the  ideas  of  colour  and  sound. 

Supposing  it,  then,  established  that  each  function  of  the  mind  is 
exercised  by  a  separate  portion  of  the  brain,  let  us  next  inquire  whether 
observation  can  furnish  us  with  any  means,  of  determining  the  precise 
nature  of  the  function,  to  which  each  particular  organ  is  subservient. 
Although  it  is  clear  that  the  adaptation  of  each  organ  to  the  performance 
of  its  office,  must  be  wholly  dependent  on  its  particular  organization, 
yet  it  is  equally  evident  that  no  consideration  of  its  general  structure, 
as  shown  to  us  by  anatomy,  can  teach  us  a  priori  what  such  function 
really  is,  and  still  less  what  may  be  its  degree  of  energy,  or  its  peculiar 
quality  and  modifications.  The  energy  of  the  function  must  in  all 
cases  depend  on  certain  conditions  of  the  organ,  such  as  the  perfection 
of  its  original  constitution,  its  elaborate  texture,  its  relative  size,  and 
the  degree  of  exercise  it  has  received  ;  and  will  also  be  regulated  by 
the  influence  which  other  faculties  may  exert  on  its  operations.  The 
only  one  among  these  conditions,  which  is  open  to  observation,  is  the 
relative  size  of  the  organ.  In  general,  we  find  that  the  properties  of 
bodies  act  with  an  energy  proportionate  to  their  size.  A  large  load- 
stone attracts  a  greater  mass  of  iron  than  a  small  loadstone.  A  large 
muscle,  in  like  manner,  is  stronger  than  a  small  one.  If  the  nerves 
of  the  external  senses  be  larger  on  one  side  of  the  bod)',  the  functions 
on  that  side  are  also  stronger.  Comparative  physiology  shows  us  that 
the  olfactory,  optic,  and  auditory  nerves  of  those  animals  which  are 
distinguished  for  the  excellence  of  their  smell,  sight,  or  hearing,  are 
marked  by  being  numerous  and  large,  evincing  a  more  elaborate  deve- 
lopment. The  coincidence  is  so  uniform  as  to  justify  the  general 
inference,  that  wherever  any  organ  is  met  with  in  a  higher  state  of 
development,  we  may  there  expect  to  find  the  power  dependent  on  it 
increased  in  energy  in  the  same  proportion.  May  not  this  analogy  be 
fairly  extended  to  the  organs  which  compose  the  brain?  Our  present 
object,  it  must  be  recollected,  is  not  to  determine  every  degree  of 
activity  existing  in  a  cerebral  part,  but  merely  the  nature  of  its  func- 
tion ;  and  for  this  purpose  the  indication  afforded  by  its  comparative 
size,  in  different  cases,  will  suffice. 

We  may  observe  in  different  individuals  a  considerable  variation  in 
the  proportional  development  of  different  parts  of  the  brain.  It  is 
reasonable  to  suppose,  that  the  organs  which  are  more  developed  in 
one  person  than  in  others,  will  be  more  active,  and  manifest  them- 
-selves    with   more   energy,   than   those   which   are    less   developed. 


CORRESPONDENCE    BETWEEN    THE    SKULL    AND    BRAIN.         471 

Those  which  are  comparatively  small  we  may  expect  to  be  less 
active,  and  the;r  powers  more  feebly  exerted.  Let  us  tlien  select 
as  the  subjects  of  observation  such  persons  as  ar^  marked  by 
strong  peculiarities  of  mind  or  character,  and  especially  such  as  are 
endowed  with  a  partial  genius,  as  it  is  called  ;  that  is,  who  manifest 
in  a  very  high  degree  any  particular  faculty  of  mind:  let  us  note  the 
peculiarities  in  the  form  of  their  heads,  and  observe  what  organs  in 
them  are  of-an  unusually  large  size.  By  repeated  comparisons  we  sjiall 
arrive  at  the  knowledge  of  the  particular  organ  in  which  that  faculty 
resides.  The  converse  method,  on  the  other  hand,  must  be  pursued 
with  those  who  betray  a  singular  deficiency  of  power  in  any  faculty. 
With  such  persons  we  must  endeavour  to  discover  what  particular  part 
of  the  brain  exhibits  an  imperfect  development.  The  results  of  both 
these  modes  of  determining  the  functions  of  each  organ,  when  com- 
pared together,  will  correct,  and,  if  just,  will  ultimately  corroborate 
each  other.  Experience,  multiplied  and  extended,  will  finally  confirm 
and  establish  our  conclusions,  and  complete  the  system  in  all  its  parts. 

But  the  living  brain  can  never  be  exposed  to  observation,  and,  from 
the  nature  of  its  substance,  loses  much  of  its  form  and  texture  soon 
after  death.  It  may  appear  impossible  to  discover  the  form  or  size  of 
particular  parts  of  the  brain  during  life,  since  the  whole  mass  is  inclosed 
in  the  bony  case  of  the  skull,  of  which  the  thickness  varies  in  different 
parts  ;  and  since  the  skull  itself  cannot  be  immediately  inspected,  being 
covered  by  muscles  and  integuments,  which,  by  contributing  to  smooth 
all  the  inequalities  of  its  surface,  must  preclude  us  from  forming  an 
exact  estimate  of  its  real  shape.  This  obvious  objection  to  the  proposed 
inquiry,  Drs.  Gall  and  Spurzheim  labour  to  remove  by  the  following 
considerations.  If  we  attend  to  the  succeseive  stages  of  the  growth  of 
the  skull,  we  find  that  its  ossification  begins  at  different  points ;  and 
the  bony  processes  extend  in  divergent  lines,  adapting  themselves 
exactly  to  the  form  and  size  of  the  cerebral  parts  they  are  destined  to 
inclose  and  protect.  Whatever  violence  may  be  done  to  the  bones  of 
the  skull  during  birth,  they  soon  return  to  their  natural  state,  partly 
from  their  elasticity,  and  partly  from  the  inherent  powers  of  the  brain, 
which  tend  constandy  to  restore  its  original  shape.  The  compression 
of  the  brain  is  besides  of  too  transient  a  nature  to  produce  any  perma- 
nent change  in  the  primitive  forms  either  of  the  skull  or  of  the  brain. 
If  it  ever  amounted  to  what  could  irrecoverably  derange  the  organiza- 
tion, and  hinder  its  future  development,  the  necessary  consequence  of 
such  a  degree  of  violence  would  be  death  or  idiocy. 

In  the  progress  of  its  growth,  the  increasing  dimensions  of  the  skull 
keep  pace  with  those  of  the  brain.  All  the  cerebral  parts  do  not  increase 
simultaneously;  and  this  partial  development  is  equally  observable  in 
the  skull.  The  forehead,  for  instance,  which  at  birth  is  narrow  and 
flat,  grows  wider  and  more  prominent  from  the  age  of  three  months  to 
that  of  eight  or  ten  years.  After  this  period,  the  middle  part  of  the 
forehead  is  less  developed  in  proportion  to  the  other  parts.  The  neck 
of  the  child  is  very  small,  because  the  cerebellum,  which  is  situate  at 
the  inferior  occipital /ossa?,  is  not  yet  developed  ;  but  in  proportion  as 
this  organ  increases  in  size,  the  skull  grows  prominent  at  that  part. 


472  APPENDIX. PHRENOLOGY. 

The  same  happens  with  all  the  other  cerebral  parts  which  increase 
progressively.  The  shape  of  the  skull  cannot  be  in  any  degree  influenced 
by  external  causes,  such  as  occasional  pressure  in  one  direction,  as 
happens  in  carrying  burdens  on  the  head,  or  artificial  modelling  of  the 
heads  of  infants,  as  is  asserted  to  be  practised  among  the  Caribs  and 
other  savage  nations.  In  other  parts  of  the  body  we  may  remaik,  that 
whatever  soft  parts  are  inclosed  in  bones,  the  shape  of  the  latter  is 
adapted  to  the  dimensions  of  the  former,  and  is  regulated  by  the  changes 
they  undergo  ;  the  ribs,  and  even  the  spine,  yield  to  the  pressure  of  an 
abscess,  or  the  enlargement  of  an  aneurism  ;  and  the  bones  of  the  face, 
in  like  manner,  make  way  for  the  increase  of  tumours,  and  adapt 
themselves  to  the  new  form  these  render  necessary.  By  experience  in 
feeling  the  living  head,  we  may  readily  learn  to  distinguish  the  form  of 
the  bones  which  lie  beneath  the  integuments.  The  observation  of  the 
shape  of  the  skull,  or  of  the  head,  is  therefore  capable  of  giving  us 
exact  information  as  to  the  relative  size  and  shape  of  the  different  parts 
of  the  brain,  and  on  the  knowledge  thus  obtained  is  founded  the  art  of 
Cranioscopy. 

In  practising  this  method,  however,  it  is  necessary  to  guard  against 
several  sources  of  error.  We  must  take  into  account  several  protu- 
berances, which  belong  to  the  natural  state  of  the  skull,  and  which  had 
some  particular  destinations  foreign  to  the  immediate  functions  of  the 
brain  ;  such  as  the  mastoid  processes  behind  the  ears,  the  crucial  spine 
of  the  occiput,  the  zygomatic  processes,  and  the  frontal  sinuses.  The 
cerebral  parts,  situate  behind  the  orbits,  indeed,  require  some  exercise 
on  the  part  of  the  organoscope,  in  order  to  be  exactly  determined.  The 
development  may  be  perceived  by  the  configuration  and  position  of  the 
eyes,  and  by  the  circumference  of  the  orbits.  It  is  therefore  necessary 
to  examine  whether  the  eyeball  is  prominent  or  hidden  in  the  orbit, 
whether  it  is  depressed  or  pushed  sideward,  inwai-d,  or  outward.  Ac- 
cording to  this  position  of  the  eyeball,  we  may  judge  that  such  or  such 
part  of  the  brain,  which  is  situate  against  such  or  such  part  of  the  orbit, 
is  more  or  less  developed.  The  functions  of  those  organs,  which  lie 
wholly  at  the  basis  of  the  brain,  can  be  ascertained  only  by  examina- 
tion after  death. 

It  may  be  objected,  that  the  organs  are  not  confined  to  the  surface, 
or  convolutions  of  the  brain  ;  but  although  this  be  the  case,  and  al- 
though they  really  extend  from  the  surface  to  the  basis  of  the  brain^  or 
medulla  oblongata,  yet  the  degree  in  which  they  are  expanded  at  the 
surface,  where  they  form  the  convolutions,  will  indicate,  in  general, 
the  relative  magnitude  of  the  whole  organ.  The  analogy  of  the  five 
senses,  of  which  the  peripheric  expansions  indicate  the  development 
of  their  respective  nerves,  shows  the  reasonableness  of  this  supposition. 
From  a  large  eye,  implying  a  large  retina,  or  peripheric  expansion  of 
the  optic  nerve,  we  naturally  infer  that  the  nerve  itself  is  of  considera- 
ble magnitude  :  may  we  not  draw  the  same  conclusion  with  regard  to 
the  organs  of  the  moral  sentiments  and  intellectual  faculties,  whenever 
we  find  that  the  convolutions,  which  are  their  peripheric  expansions, 
are  much  developed  ? 

In  feeling  for  the  organ.  Dr.  Gall  recommends  the  use,  not  of  the 


THE    PROPENSITIES.  473 

fingers,  but  of  the  middle  of  the  pahii  of  the  hand;  and  declares  that 
habit,  as  well  as  a  certain  natural  delicacy  of  tact,  is  necessary  to 
qualify  a  person  to  make  these  observations  with  certainly  and  success. 
We  are  warned,  also,  to  confine  our  observations  to  young  and 
grown-up  persons  in  the  flower  of  their  age  ;  for  at  an  advanced  period 
of  life  the  brain  diminishing  by  degrees,  and  retiring  from  the  skull, 
leads  to  the  recession  of  its  inner  table,  and  conseijuent  inequality  in 
its  thickness,  which  renders  it  impossible  to  judge  exactly  of  the  size 
or  shape  of  brain  from  that  of  the  head.  Analogous  changes  occur  in 
the  skulls  of  some  lunatics,  and  occasion  similar  difiicullies  in  applying 
the  rules  of  cranioscopy.  It  is  also  to  be  considered,  that  our  aim  is 
to  distinguish  the  size,  and  not  the  mere  prominence  of  each  organ. 
If  one  organ  be  much  developed  and  the  neighbouring  organ  very  little, 
the  developed  organ  presents  an  elevation  or  protuberance,  but  if  the 
neighbouring  organs  be  developed  in  proportion,  no  protuberance  can 
be  perceived,  and  the  surface  is  smooth. 

We  have  already  stated  the  mode  in  which  Dr.  Gall  proceeded  to 
apply  and  to  verify  these  principles ;  it  is  now  time  that  we  should 
present  our  readers  with  the  result  of  his  labours. 

He  arranges  the  faculties  of  ihe  mind,  with  their  corresponding 
organs,  according  as  they  relate  to  the  feelings  and  to  the  intellect : 
the  first  class  comprehending  ihe  propensities,  a\\  which  are  common 
to  man  and  animals,  and  the  sentiments,  which  constitute  what  the 
French  denominate  fame,  and  the  Germans  gemiith  ;  and  the  second 
class  comprising  the  faculties  by  which  we  acquire  knowledge,  or  the 
knowing  faculties,  as  he  terms  them  ;  and  also  the  reflecting  faculties, 
which  last  compose  what  the  French  call  Vesprit,  the  Germans  glidst, 
and  what  we  should  generally  understand  by  the  term  intellect.  He 
finds  that  the  organs  of  those  faculties,  which  men  possess  in  common 
with  animals,  are  situate  towards  the  basis  and  back  part  of  the  brain  ; 
while  those  of  the  superior  faculties,  which  are  peculiar  to  man,  are 
placed  somewhat  higher;  and  tlie  organs  subservient  to  the  intellectual 
faculties  occupy  exclusively  the  forehead.  The  total  number  of  special 
faculties  is  thirty-three,  as  may  be  seen  by  the  following  enumeration. 

1.  Of  the  faculties  common  to  man  and  animals,  the  first  is  that 
physical  propensity  which  has  for  its  final  purpose  the  continuance  of 
the  species.  The  cerebellum,  a  part  which  occupies  the  lowest  situa- 
tion in  the  encephalon,  is  affirmed  to  be  the  organ,  the  actions  of  which 
give  rise  to  this  propensity.  Accident  led  Dr. 'Gall  to  this  discovery, 
by  his  noticing  the  size  of  iho  back  of  the  neck  in  a  lady  whose  cha- 
racter, in  respect  to  this  passion,  was  not  equivocal :  and  subsequent 
observation  on  an  extensive  scale,  both  in  the  human  subject  and  in  the 
lower  animals,  have  abundantly  confirmed  him  in  his  opinion.  The 
following  are  the  leading  arguments  on  which  he  has  rested  it.  First, 
the  great  size  of  the  organ  indicates  the  importance  of  the  function  to 
which  it  is  subservient,  and  there  is  no  cause,  except  the  existence  of 
such  an  organ  in  the  brain,  that  is  adequate  to  account  for  this  propen- 
sity. The  function  of  copulation  takes  place  only  in  those  animals 
which  have  a  nervous  mass  or  cerebellum.  Throughout  the  whole 
class  of  quadrupeds,  the  neck  of  the  male  is  thicker  than  that  of  the 

40* 


474  APPENDIX. PHRENOLOGY. 

female,  as  may  be  observed  particularly  in  the  bull,  the  ram,  and  the 
stallion.  It  is  also  remarked  that  vigorous  pigeons  are  distinguished 
by  the  size  of  their  necks.  The  development  of  the  cerebellum  is 
simultaneous  vi^ith  that  of  the  genital  organs  at  the  period  of  puberty, 
and  early  castration  prevents  its  development,  as  well  as  that  of  the 
beard,  and  the  organs  of  the  voice.  Wounds  of  the  neck  have  been 
observed  by  Hippocrates  to  be  sometimes  followed  by  impotency.  In 
other  cases,  however,  they  produce  erotic  excitement.  Apollonius 
^  Rhodius,  in  speaking  of  the  love  of  Medea,  represents  her  as  suffering 
a  violent  pain  in  the  back  of  her  neck.  A  case  occurred  to  Professor 
Reinhold,  at  Leipsig,  in  which  an  excitement  of  the  genital  organs 
succeeded  the  introduction  of  a  seton  in  the  neck,  in  a  boy  who 
laboured  under  ophthalmia.  Spirituous  frictions  on  the  neck  in  hyste- 
rical fits  are  very  useful.  J^astly,  the  position  of  the  cerebellum  is 
supposed  to  prove  its  destination.  After  hunger  and  thirst,  no  function 
is  more  necessary  than  that  of  propagating  the  species.  This  function 
is  the  most  common  in  animals,  after  nutrition,  and  the  cerebellum  is 
in  the  inferior  part  of  the  head.  Hence  it  is  probable,  that  it  is  destined 
to  the  propensity  of  propagating,  or  that  it  is,  as  Dr.  Spurzheim  ex- 
presses it,  the  organ  of  amativeness. 

2.  Philoprogenitiveness,  or  the  love  of  progeny,  the  a-Tofyn  of  the 
Greeks,  has  its  seat  in  those  convolutions  of  the  brain  situate  imme- 
diately above  the  hind  part  of  the  tentorium,  and  corresponding,  there- 
fore, on  the  outside  of  the  skull  with  the  crucial  spine  of  the  occiput. 
Dr.  Gall  had  observed  a  distinct  protuberance  on  this  part  of  the  head 
in  women,  and  comparing  the  skulls  in  his  collection,  found  a  similar 
elevation  on  the  skulls  of  children,  and  on  those  of  monkeys.  During 
five  years  he  was  in  search  of  a  faculty  that  was  common  to  all  the 
subjects  of  those  observations,  and  was  in  the  habit  of  suggesting  this 
difficulty  to  his  auditors.  At  length  a  clergyman  who  attended,  ob- 
served that  monkeys  have  much  attachment  to  their  progeny.  The 
Doctor  pursued  this  idea,  and  found  that  it  applied  perfectly  to  the 
observed  appearances,  as  the  development  of  this  part  coincided  always 
with  the  energy  of  this  propensity.  In  animals  it  is  generally  larger 
in  the  females  than  in  the  males  of  the  same  species.  This  rule  holds 
good  in  the  human  subject,  although  it  is  liable  to  occasional  excep- 
tions ;  for  there  are  men  who  manifest  the  strongest  propensity  to 
associate  with  children,  and  in  whom  we  accordingly  find  this  organ 
larger  than  in  the  generality  of  women.  In  negroes  we  find  this  organ 
more  prominent  than  in  Europeans.  In  the  cuckoo,  the  crocodile,  and 
other  animals  to  whom  nature  has  not  appointed  the  office  of  rearing 
their  progeny,  this  organ  is  extremely  defective.  The  crime  of  infan- 
ticide is  more  likely  to  be  perpetrated  by  mothers  in  whom  this  organ 
is  deficient  in  size  ;  and  accordingly  out  of  29  women  who  were  guilty 
of  this  crime,  Dr.  Gall  found  25  who  had  this  organ  extremely  small. 
On  the  other  hand,  a  female,  who,  being  seized  with  delirium  during 
child-birth,  imagined  that  she  was  pregnant  with  five  children,  was 
found  to  have  this  organ  unusually  large.  It  must,  no  doubt,  have 
been  of  gigantic  dimensions  in  the  lady,  who,  stricken  by  the  curse  of 
the  gipsey  whom  she  had  refused  to  relieve,  was  impressed  with  the 


THE    PROPENSITIES. 


47h 


belief  that  she  was  about  to  give  birth  to  as  many  children  as  there  are 
days  in  the  year. 

3.  The  organ  of  Inhabitiveness,  or  the  propensity  which  some  ani- 
mals, such  as  the  chamois  and  the  wild-goat,  have  to  inhabit  high  situa- 
tions, is  placed  still  higher  in  the  occiput  than  the  former,  in  a  line 
proceeding  towards  the  top  of  the  head.  In  animals  of  the  same 
species  which  live  in  low  countries,  we  do  not  meet  with  an  equal 
degree  of  protuberance  in  this  part  of  the  brain,  as  is  observable  in 
those  which  prefer  living  in  elevated  and  mountainous  districts.  This 
is  seen  even  in  the  rat,  some  varieties  of  which  choose  for  their  dwelling 
corn-lofts  or  the  higher  parts  of  a  house,  while  others  prefer  living  in 
the  cellars.  This  faculty  is  not  very  active  in  man ;  but  Dr.  Gall 
conceived  that  it  was  in  him  allied  to  pride  and  haughtiness.  Dr. 
Spurzheim,  however,  disclaims  this  doctrine ;  as  he  thinks  it  impossi- 
ble to  confound  the  "  instinct  of  physical  height''  with  the  moral  senti- 
ment of  self-love  and  pride.  Mr.  Combe,  conceiving  that  this  organ 
has  a  more  extensive  sphere  of  action,  and  that  it  confers  the  power  of 
being  conscious  of  every  thing  going  on  in  the  mind,  and  of  concen- 
trating the  attention,  terms  this  power  Concentrativeness. 

4.  The  organ  oi  Jldhesiveness,  or  the  propensity  to  attach  ourselves 
to  persons,  animals,  or  other  objects,  is  situate  on  each  side  of  the 
former,  immediately  under  the  lambdoidal  suture,  and  gives  a  fulness 
to  the  lateral  and  posterior  part  of  the  head.  This  organ  is  the  source 
of  friendship,  moral  love,  society,  marriage,  and  attachment  of  all 
kinds.  Dogs  have  it  in  an  eminent  degree,  especially  those  races 
whose  fidelity  and  constancy  are  characteristic,  as  the  terrier,  spaniel, 
and  lap-dog.  It  is  less  prominent  in  the  butcher's  dog,  greyhound, 
and  mastiff.  It  was  very  large  in  a  notorious  highwayman  at  Vienna, 
distinguished  equally  as  a  robber  and  a  friend,  and  who  chose  rather  to 
die  than  to  betray  his  confederates. 

5.  Comhaliveness,  or  the  propensity  to  fight,  results  from  the 
operation  of  an  organ,  situate  immediately  behind  the  ears  on  each  side, 
at  a  part  corresponding  to  the  posterior  inferior  angle  of  the  parietal 
bone,  and  behind  the  mastoid  process.  It  is  the  seat  of  anger,  as  well 
as  of  pugnacity  ;  and  its  locality  is  fully  established,  in  Dr.  Gall's 
estimation,  by  an  extensive  series  of  facts.  His  first  discovery  of  the 
seat  of  this  faculty,  was  from  his  observation  of  the  head  of  the  Austrian 
General  Wurraser;  and  it  was  subsequently  confirmed  by  the  experi- 
ments we  have  already  mentioned  which  he  made  on  boys  he  had 
collected  from  the  street.  The  breadth  of  the  occiput  is  a  criterion  of 
the  spirit  and  courage  of  horses,  dogs,  &c.  The  bull-dog  and  pug-dog 
are  in  this  respect  superior  to  the  mastiff.  The  hysena  is  strongly 
contrasted  with  the  hare,  and  the  guinea-hen  with  the  robin  red-breast. 

6.  Destrucfiveness,  or  the  propensity  to  destroy  in  general,  but 
more  especially  to  destroy  life,  has  its  seat  just  above  the  ears  ;  the 
prominence  of  which  part  will  account  for  the  strange  pleasure  which 
some  people  take  in  killing  or  tormenting  animals,  in  seeing  executions, 
and  for  their  inclination  to  commit  murder.  Among  animals,  this 
instinct  for  blood  is  strongly  marked  in  the  carnivorous  tribes,  especially 
iji  the  lion,  tiger,  and  others  of  the  feline  tribe  ;  and  the  breadth  of  their 


476  APPENDIX. PHRENOLOGY. 

skulls  in  this  part  shows  us  the  great  size  of  this  organ,  compared  with 
that  of  their  victims,  the  sheep,  the  goat,  or  the  hare.  The  heads  of 
murderers  have  in  general  been  found  to  possess  a  visible  prominence  at 
this  place.  When  the  band  of  ferocious  robbers  and  assassins,  who  so 
long  infested  the  left  banks  of  the  Rhine,  under  Schinderhanns,  had 
been  caught,  and  a  number  of  them  executed.  Dr.  Gall  found  this  organ 
strikingly  developed  in  the  heads  of  these  banditti.  This  propensity 
is  frequently  strong  in  children,  in  idiots,  and  in  madmen.  Its  object, 
in  the  lower  animals,  is  evidently  to  procure  the  food  on  which  nature 
destined  they  should  live;  yet  some  animals  kill  more  than  is  necessary 
for  their  nourishment.  In  man  this  propensity  presents  different  degrees 
of  activity,  from  a  mere  indifference  to  the  pain  of  animals,  to  the  plea- 
sure of  seeing  them  killed  or  tortured,  or  even  the  most  imperious 
desire  to  kill.  Dr.  Gall  called  this  faculty  murder ;  but  Dr.  Spurzheim 
thinks  it  produces  the  propensity  to  destroy  in  general,  without  deter- 
mining the  object  to  be  destroyed,  or  the  manner  of  destroying  it.  "  It 
gives,"'  says  he,  "  the  propensity  to  pinch,  scratch,  bite,  cut,  break, 
pierce,  devastate,  demolish,  ravage,  burn,  massacre,  strangle,  butcher, 
suffocate,  drown,  kdl,  poison,  murder,  and  assassinate."  It  would 
seem,  therefore,  that  this  organ  has  a  great  deal  to  answer  for. 

7.  Constructive/less,  the  propensity  to  build,  or  the  disposition  to- 
the  mechanical  arts,  is  indicated  by  the  development  of  the  brain  at  the 
temples.  Dr.  Gall  found  this  to  be  the  case  in  great  mechanicians, 
architects,  sculptors,  and  designers  ;  and  also  in  the  skulls  of  the  beaver, 
maririot,  held- mouse,  and  rabbit,  which  construct  habitations.  Hares, 
on  the  contrary,  which  lie  in  the  fields,  have  this  organ  defective, 
although  in  general  they  resemble  rabbits.  He  possesses  the  skull  of 
a  milliner  of  Vienna,  who  had  a  good  taste,  and  understood  perfectly 
the  art  of  changing  the  forms  of  her  merchandise  ;  in  this  skull  the 
organ  in  question  is  prominent.  It  is  by  means  of  this  faculty  that  birds 
build  nests,  savages  huts,  and  kings  palaces.  It  produces  also  fortifi- 
cations, ships,  engines  of  war,  manufactures  of  all  kinds,  furniture, 
clothes,  toys,  &c.  There  was  a  lady  at  Paris,  who,  every  time  she 
was  pregnant,  felt  the  greatest  propensity  to  build.  The  excessive 
size  of  this  organ  may  lead  a  man  to  ruin  liis  family  by  building,  or  to 
coin  false  money. 

8.  Covetiveness,  or  the  propensity  to  covet,  gather,  and  acquire 
without  determining  the  object  to  be  acquired,  or  the  manner  of  jtc- 
quiring  it,  has  its  organ  situate  at  the  temples,  on  the  anterior  inferior 
angle  of  the  parietal  bone.  This  faculty  gives  a  desire  for  ail  that 
pleases  ;  money,  property,  animals,  servants,  land,  cattle,  or  any  thing 
upon  earth.  It  produces  egotism  and  selfishness,  and  may,  when 
abused,  lead  to  usury,  plagiarism,  fraud,  or  theft.  The  instinct  of 
stealing,  it  is  asserted,  is  not  always  the  effect  of  bad  educalio'n,  of 
poverty,  idleness,  or  the  want  of  religion  and  moral  sentiment.  This 
truth,  says  Dr.  Spurzheim,  is  so  generally  felt,  that  every  one  winks 
at  a  little  theft  committed  by  rich  persons,  who  in  other  respects  con- 
duct tliemselves  well.     Mr.  Combe  terms  this  faculty  Jicquisiliveness. 

9.  The  organ  of  Secretiveness,  or  the  propensity  to  conceal,  or  to 
be  clandestine  in  general,  is  situate  in  the   middle   of  the   side  of  the 


THE   SENTIMENTS.  477 

head,  above  the  organ  of  the  propensity  to  destroy.  Dr.  Gall  first 
observed  this  organ  in  a  person  who  had  many  debts,  but  who  had  the 
address  to  conceal  his  real  situation,  so  that  the  creditors  could  have 
no  knowledge  of  each  other.  He  ascribes  to  this  faculty  cunning, 
prudence,  the  s  avoir  /aire.,  the  capacity  of  finding  means  necessary  to 
succeed,  hypocrisy,  lies,  intrigues,  dissimulation,  duplicity,  falsehood; 
in  poets,  the  talent  of  finding  out  interesting  plots  for  romances  and 
dramatic  pieces  ;  and  finally,  the  quality  of  slyness  in  animals,  as  in 
the  fox  and  the  cat,  who  conceal  their  intentions,  and  are  clever  in 
hiding  themselves. 

To  the  second  genus  of  the  order  of  feelings,  namely,  Sentiments, 
belong  the  following  faculties: — 

10.  Self-love,  or  self-esteem.  Dr.  Gall  first  noticed  this  organ, 
which  lies  in  the  middle  of  the  upper  posterior  point  of  the  head,  in  a 
beggar,  who  stated  that  he  was  reduced  to  his  present  condition  by  his 
pride,  which  made  him  neglect  his  business.  The  animals  endowed 
with  this  organ  are  the  turkey-cock,  peacock,  horse,  &c.  Dr.  Gall 
thought  this  organ  is  the  same  as  that  of  the  faculty  which  makes  cer- 
tain animals  dwell  upon  mountains  ;  but  Dr.  Spurzheim,  as  we  have 
already  observed,  draws  a  line  of  distinction  between  them.  The  too 
great  activity  of  this  faculty  is  the  cause  of  various  abuses,  as  pride, 
haughtiness,  disdain,  contempt,  presumption,  arrogance,  and  insolence. 
The  want  of  it  disposes  to  humility.  It  is  said  to  be  more  active  in 
women  than  in  men,  and  that  its  excess '  is  sometimes  the  cause  of 
madness. 

11.  Love  of  Approbation.  Persons  fond  of  the  good  opinions  of 
others,  have  the  upper  posterior  and  lateral  part  of  the  head  much 
developed.  This  may  be  called  the  organ  of  ambition  or  vanity, 
according  to  the  object,  which  may  be  of  various  kinds.  A  coachman 
endowed  with  this  faculty  is  pleased  if  his  manner  of  conducting  horses 
be  approved  ;  and  a  general  is  elated  if  he  be  applauded  by  his  nation 
for  leading  his  army  to  victory.  This  faculty  is  more  active  in  women 
than  in  men,  and  even  in  certain  nations  more  than  in  others.  More 
women  become  mad  from  this  cause  than  men. 

12.  Organ  of  Cautiousness.  Two  persons  at  Vienna  were  known 
to  be  remarkable  for  their  extreme  irresolution.  One  day,  in  a  public 
place,  Dr.  Gall  stood  behind  them,  and  observed  their  heads.  He 
found  them  extremely  large  on  the  upper  posterior  part  of  both  sides 
of  the  head.  Hence  he  derived  the  first  idea  of  this  organ.  Circum- 
spect animals  also,  as  the  stag,  roe,  pole-cat,  otter,  and  mole,  and  those 
which  place  sentinels  to  warn  them  of  approaching  danger,  as  the 
chamois,  cranes,  starlings,  and  bustards,  have  this  cerebral  part  much 
developed.  This  faculty  produces  precaution,  doubts,  demurs ;  and,  in 
general,  exclaims  continually  "  take  care.'''  It  considers  consequences, 
and  produces  all  the  hesitations  expressed  by  the  word  but.  When 
excessive,  it  produces  uncertainty,  irresolution,  unquietness,  anxiety, 
fear,  melancholy,  hypochondriasis,  and  suicide.  Dr.  Gall  finds  this 
organ  more  strongly  marked  in  children  than  in  grown  persons. 

13.  The  organ  of  Benevolence  in  man,  or  of  meekness  in  animals, 
is  situate  on  the  superior  middle  part  of  the  forehead.     In  most  ani- 


478  APPENDIX.- — PHRENOLOGY. 

mals  it  is  restrained  to  a  passive  goodness  ;  but  in  man  its  sphere  of 
activity  is  very  considerable,  producing  all  the  social  virtues,  or  in  one 
word,  Christian  charity. 

14.  The  organ  of  Veneration,  or  of  Theosophy,  occupies  the  centre 
of  the  uppermost  part  of  the  os  frontis.  Dr.  Gall  has  observed  in 
churches,  that  those  who  prayed  with  the  greatest  fervour  were  bald ; 
and  that  their  heads  were  much  elevated.  The  pictures  of  saints  show 
the  very  configuration  which  he  had  thus  noticed  in  pious  men  ;  and 
the  head  of  our  Saviour,  also,  is  generally  represented  of  this  shape. 
It  is  by  this  faculty  that  man  adores  God,  or  venerates  saints,  and  per- 
sons and  things  deemed  sacred. 

15.  The  organ  of  Hope  is  situate  on  the  side  of  that  of  veneration. 
Dr.  Spurzheim  considers  the  sentiment  of  hope  as  proper  to  man,  and 
as  a  sentiment  necessary  in  almost  every  situation ;  it  gives  hope  in 
the  present,  as  well  as  of  a  future  life.  In  religion  it  is  called  faith. 
Its  excessive  development  produces  credulity. 

16.  Ideality,  or  the  poetical  disposition.  The  heads  of  great  poets 
are  enlarged  above  the  temples,  in  an  arched  direction.  The  sentiment 
inspired  by  this  organ  is  the  opposite  of  circumspection  ;  it  renders 
us  enthusiasts,  while  circumspection  stops  our  career  by  saying 
"  take  care."  If  the  part  of  the  head  above  this  organ,  and  a  little 
backward  from  it,  be  very  much  developed,  the  person  is  disposed  to 
have  visions,  to  see  ghosts,  and  to  believe  in  astrology,  magic,  and 
sorcery. 

17.  The  faculty  of  Fighteousness,  or  Conscientiousness,  which 
produces  the  sentiment  of  just  and  unjust,  right  and  wrong,  has  its 
organ  situate  a  little  more  forward  than  the  organ  of  approbation.  It 
produces  the  sentiment  of  duty,  and  constitutes  what  is  called  con- 
science or  remorse.  Dr.  Spurzheim  admits  farther  an  organ  o^  jus- 
tice, which  he  seeks  for  on  the  side  of  the  following  organ. 

18.  Determinateness,  or  Firmness.  Dr.  Gall  observed  that  persons 
of  a  firm  and  constant  character  have  the  top  of  the  brain  much  deve- 
loped. Lavater  had  made  the  same  observation.  This  faculty  contri- 
butes to  maintain  the  activity  of  the  other  faculties  by  giving  constancy 
and  perseverance.  Its  too  great  activity  produces  infatuation,  stub- 
bornness, obstinacy,  and  disobedience.  Its  deficiency  engenders  fickle- 
ness and  inconstancy. 

To  the  order  called  Intellect,  and  the  first  genus  of  that  order,  viz. 
the  knowing  faculties,  belong  the  following  species  : 
.  19.  Individuality,  or  the  faculty  which  procures  us  the  knowledge 
of  external  beings,  after  we  have  received  impressions  from  them  by 
the  external  senses,  occupies  the  middle  of  the  lower  part  of  the  fore- 
head. Dr.  Gall  found  this  part  very  prominent,  indicating  a  great 
development  of  the  anterior  and  inferior  part  of  the  brain,  in  all  per- 
sons, who,  from  their  extensive,  but  superficial  knowledge  in  the  arts 
and  sciences,  were  capable  of  shining  and  taking  a  lead  in  conversa- 
tion. It  has  been  not  unaptly,  though  satirically  characterized  as  the 
blue-stocking  faculty.  Tame  animals  have  the  forehead  more  developed 
than  wild  ones,  and  are  more  or  less  tameable  in  proportion  as  the 
forehead  is  more  or  less  developed  ;  Dr.  Gall,  therefore,  calls  this  organ 


THE    INTELLECTUAL    FACULTIES.  479 

that  of  educability.  Dr.  Spurzheim,  however,  objects  to  this  term, 
and  has  substituted  that  of  individuality;  he  also  remarks  that  the 
organ  is  early  developed  in  children,  because  they  are  obliged  to  ac- 
quire a  knowledge  of  the  external  world. 

20.  The  organ  of  Form  leads  us  to  take  cognizance  of  the  forms  of 
objects,  with  the  existence  of  which  the  preceding  faculty  had  made 
us  acquainted.  Persons  endowed  with  it  in  a  high  degree,  have  a 
great  facility  of  distinguishing  and  recollecting  persons  ;  they  are  fond 
of  seeing  pictures,  and  if  they  make  collections,  they  collect  portraits. 
Crystallography  is  the  result  of  this  faculty.  The  conception  of 
smoothness  and  roughness  also  belongs  to  it.  This  organ  is  placed 
in  the  internal  angle  of  the  orbit,  and,  if  much  developed,  it  pushes 
the  eyeball  toward  the  external  angle,  that  is  a  little  outward  and  down- 
ward.    The  Chinese  appear  to  have  it  in  perfecton. 

21.  Size.  After  the  existence  and  figure  of  any  body,  the  mind 
considers  its  dimensions  or  size,  for  there  is  an  essential  difference  be- 
tween the  idea  of  size  and  that  of  form.  The  organ  must  therefore  be 
different ;  it  is  probably  however  in  the  neighbourhood  of  the  former. 

22.  Weight.  The  ideas  of  weight  and  resistance,  density,  softness 
and  hardness,  cannot  be  attributed  to  the  sense  of  feeling,  and  require, 
therefore,  a  particular  faculty  for  their  conception.  Its  organ  must  be 
situate  in  the  vicinity  of  the  two  last. 

23.  Colour.  The  faculty  of  conceiving  colour  is,  in  like  manner, 
totally  distinct  from  the  sense  of  vision,  or  the  faculty  of  perceiving 
light.  Its  organ  is  placed  in  the  midst  of  the  arch  of  the  eye-brows,  giv- 
ing them,  when  expanded,  a  vaulted  and  rounded  arch.  This  configura- 
tion is  characteristic  of  painters,  and  is  strikingly  displayed  in  the 
Chinese,  who  are  well  known  to  be  very  fond  of  colours.  This  faculty 
is  generally  more  active  in  womeai  than  in  men. 

24.  Space,  or  Locality.  The  faculty  of  local  memory,  by  which 
we  recollect  localities,  and  find  our  way  to  places  where  we  have  been 
before,  is  much  stronger  in  some  persons  than  in  others.  Animals  are 
also  endowed  with  it,  and  it  enables  them  to  return  to  their  dwellings 
and  their  progeny,  when  obliged  to  leave  them  in  search  of  food.  It  is 
conspicuous  in  some  dogs  ;  while  others  are  very  deficient  in  this 
respect.  The  migration  of  birds  is  the  result  of  this  faculty.  The 
pictures  and  busts  of  great  astronomers,  navigators,  and  geographers, 
as  of  Newton,  Cook,  Columbus,  &c.  present  a  great  development  of 
this  organ,  which  is  situate  under,  but  extends  a  little  beyond,  the 
frontal  sinuses.  The  swallow,  the  stork,  and  the  carrier-pigeon,  have 
all  this  organ.  This  faculty  conceives  the  places  occupied  by  the  ex- 
ternal bodies,  and  makes  space  not  only  known  to  us,  but  inspires  a 
fondness  for  this  kind  of  knowledge.  It  makes  the  traveller,  geogra- 
pher, and  landscape  painter  ;  it  recollects  localities,  judges  of  symmetry, 
measures  space  and  distance,  and  gives  notions  of  perspective. 

25.  Order.  This  faculty  enables  us  to  conceive  order.  It  gives 
method  and  order  in  arranging  objects  as  they  are  physically  related. 
Its  organ  is  probably  situate  outward,  but  not  far  from  the  organs  of 
size  and  space. 

26.  Time.  Ideas  of  time  are  the  result  of  a  distinct  faculty  ;  for  they 


480  APPENDIX. PHRENOLOGY. 

may  exist  without  those  of  order  and  number.  They  seem  to  be 
higher  in  the  scale,  and  their  organ,  accordingly,  occupies  a  higher 
place  in  the  brain. 

27.  Number.  All  the  ideas  that  are  concerned  about  unity  or 
plurality,  that  is,  about  number,  belong  to  a  faculty  whose  organ  is 
situate  in  a  part  of  the  brain  near  the  external  angle  of  the  orbit.  The 
object  of  this  faculty  is  calculation  in  general.  When  much  developed, 
the  arch  of  the  eye-brows  is  considerably  depressed,  or  is  elevated  at 
the  outer  extremity.  This  conformation  is  apparent  in  the  portraits 
and  busts  of  great  calculators,  as  Newton,  Euler,  Kastner,  Jedediah 
Buxton,  and  Pitt.  The  heads  of  negroes  are  very  narrow  at  this  part ; 
and,  in  general,  they  do  not  excel  in  this  faculty. 

28.  Tune.  The  perception  of  musical  tone  is  distinct  from  that  of 
sound,  and  implies  a  different  faculty  from  that  of  hearing.  Its  organ 
is  placed  on  the  lateral  parts  of  the  forehead.  Its  form  varies  accord- 
ing to  the  direction  and  form  of  its  convolutions.  In  Gluck  and  Haydn, 
it  has  a  pyramidal  form  ;  in  Mozart,  Viotti,  Zumsteg,  Dusseck,  and 
Crescentini,  the  external  corners  of  the  forehead  are  enlarged  but 
rounded. 

The  heads  and  skulls  of  singing  birds,  especially  the  males,  exhibit 
this  organ  fully  developed.     Monkeys  are  absolutely  destitute  of  it, 

29.  Language.  The  organ  of  the  faculty  of  learning  the  artificial 
signs  for  the  operations  of  the  mind,  of  perceiving  their  connection 
with  the  thing  signified,  and  of  remembering  them,  and  judging  of 
their  relations,  occupies  a  transverse  situation  in  the  midst  of  the 
knowing  faculties,  and  presses  upon  the  basis  of  the  orbit  of  the  eye, 
so  as  to  project  the  eye  forwards  when  much  developed.  This  pro- 
duces what  is  commonly  called  a  goggle-eye,  denoting  strong  verbal 
memory.  Sometimes  the  eyes  are  not  only  prominent,  but  also  de- 
pressed downward,  so  that  the  under  eye-lid  presents  a  sort  of  roll,  or 
appears  swollen.  Such  persons  are  fond  of  philology,  that  is,  they 
like  to  study  the  spirit  of  different  languages. 

The  second  genus  of  the  order  Intellect,  viz.  the  reflecting  faculties, 
contains  the  following  species  : — 

30.  Comparison.  This  faculty  compares  the  sensations  and  ideas 
of  all  the  other  faculties ;  and  points  out  their  difference,  analogy, 
similitude,  or  identity.  Dr.  Gall  observed  various  persons,  who,  in 
every  conversation,  had  recourse  to  examples,  similitudes,  and  ana- 
logies, in  order  to  convince  others  ;  and  seldom  to  reasoning  and  phi- 
losophical arguments.  In  them  he  found,  in  the  midst  of  the  superior 
part  of  the  forehead,  an  elevation  which  presented  the  form  of  a  re- 
versed pyramid,  and  he  named  this  organ,  according  to  its  functions, 
the  organ  of  analogy.  Nations  who  have  this  faculty  in  a  high  degree 
are  fond  of  figurative  language. 

31.  Causality.  This  faculty  examines  causes,  considers  the  rela- 
tions between  cause  and  effect,  and  always  prompts  men  to  ask,  Why  ? 
Persons  fond  of  metaphysics  have  the  superior  part  of  the  forehead 
much  developed  and  prominent  in  a  hemispherical  form,  as  Mendel- 
sohn, Kant,  Fichte,  and  others.     The  ancient  artists  have  given  to 


APPLICATIONS   OF   PHRENOLOGY.  481 

Jupiter  Capitolinus  a  forehead  more  prominent  than  to  any  other  an- 
tique head. 

32.  Wit.  Persons  who  have  this  faculty,  who  write  like  Sterne, 
Voltaire,  Piron,  &c.  have  the  superior  external  parts  of  the  forehead 
elevated.  The  essence  of  tiiis  faculty  consists  in  its  peculiar  manner 
of  comparing,  which  always  excites  gaiety  and  laughter.  Jest,  raillery, 
mockery,  ridicule,  irony,  &c.  are  its  offsprings. 

33.  Imitation.  Persons  who  have  a  considerable  elevation  of  a 
semi-globular  form  at  the  sv*perior  part  of  the  forehead,  have  the  faculty 
of  imitating,  with  great  precision,  the  gestures,  voice,  manners,  and, 
in  general,  all  the  natural  manifestations  of  men  and  animals.  They 
have  a  disposition  to  be  actors,  and  are  prone  to  gesticulation.  This 
organ  is,  in  general,  more  developed  in  children  than  in  adult  persons. 

To  the  above  catalogue  of  the  organs  enumerated  by  Dr.  Spurzheim, 
Mr.  Combe  has  since  added  the  two  following,  namely, 

34.  The  organ  of  Wonder  (situate  immediately  above  Ideality,  in 
the  lateral  parts  of  the  anterior  regions  of  the  vertex),  which  occasions 
the  belief  in  the  reality  of  ghosts,  and  other  mysterious  af)paritions  and 
visitations,  and  inspires  a  love  for  all  that  is  marvellous  and  super- 
natural, and  also  a  taste  for  novelty  and  fashion.  When  largely 
developed,  it  excites  young  men,  born  and  bred  in  inland  situations,  to 
choose  the  sea  as  a  profession.* 

35.  The  organ  oi Eventuality,  which,  when  large,  gives  prominence 
or  a  rounded  fulness  to  the  middle  of  the  forehead.  "  The  function  of 
this  faculty  is  to  take  cognizance  of  changes,  events,  or  active  pheno- 
mena, indicated  by  active  verbs.  In  such  expressions  as  the  rock 
falls,  the  HORSE  gallops,  the  battle  \s  fought,  the  substantive  springs 

from  Individuality,  and  the  verb  from  Eventuality.  It  prompts  to 
investigation  by  experiment,  while  Individuality  leads  to  observation 
of  existing  things.  Individuality  gives  the  tendency  to  personify 
abstract  ideas,  such  as  Ignorance  and  Wisdom  ;  and  Eventuality  to 
represent  them  as  acting.  An  author  in  whom  Individuality  is  large, 
and  Eventuality  small,  will  treat  his  subject  by  description  chiefly, 
and  one  in  whom  Eventuality  is  large  and  Individuality  small,  will 
narrate  actions,  but  deal  little  in  physical  description. "t 

Two  other  primary  faculties  are  mentioned  by  Mr.  Combe ;  one, 
which  he  terms  Alimentiveness,  or  the  desire  of  eating  and  drinking  ; 
and  another,  which  had  been  called  by  Spurzheim  VitativenesS,  or  the 
Love  of  Life;  but  the  seat  of  these  powers  has  not  been  exactly 
determined. 

Excepting  in  the  case  of  idiots,  all  the  thirty-five  organs  above  des- 
cribed are  possessed  by  every  persbn,  but  they  exist  in  greater  or  less 
perfection  in  different  individuals.  Peculiarity  of  character  is  the  result 
of  irregularity  in  the  original  structure,  or  inequality  in  the  relative 
development  of  the  several  organs  ;  circumstances  which,  according  as 
they  are  diversified,  lay  the  foundation  of  every  excellence,  as  well  as 
constitute  the  fatal  sources  of  vice  and  depravity.  These  doctrines 
should,  however,  by  no  means  be  understood  as  lending  their  sanction 

*  System  of  Phrenology,  fourth  edition,  p.  381.  -j-  lb.  518. 

41 


482  APPENDIX. PHRENOLOGY. 

to  the  latter ;  for  crimes  are  considered  as  flowing  from  the  abuse  ,of 
certain  faculties,  and  as  still  requiring  for  their  prevention  the  coun- 
teracting influence  of  morality,  and  the  salutary  coercion  of  law.  It 
must  be  of  importance  to  every  individual  to  know,  if  such  knowledge 
be  attainable,  what  is  the  degree  of  energy  of  the  propensities  and 
other  faculties  with  which  he  may  have  been  naturally  and  originally 
endowed  ;  because  every  organ  and  corresponding  faculty  may  be 
invigorated  by  proper  exercise.  The  business  of  education  will  ac- 
cordingly consist  in  exciting  or  restraining  the  development,  according 
to  their  natural  deficiency  or  exuberance.  Phrenology,  by  pointing 
out  what  are  the  strongest  faculties  in  a  child,  will  enable  us  to  adopt 
the  best  plan  of  intellectual,  as  well  as  moral  discipline  ;  will  assist  us 
in  regulating  his  passions,  and  maintaining  a  due  balance  between  all 
his  moral  sentiments  ;  and  guide  us  in  the  choice  of  a  profession  for 
our  pupil,  conformable  to  the  particular  bent  of  his  genius.  "  What 
benefit  would  arise  to  society,"  says  Mr.  Forster,  the  zealous  advocate 
of  these  doctrines,  ^'should  we  be  enabled  to  make  a  just  election  of 
objects  in  youth,  to  be  placed  in  situations  capable  of  ripening  their 
naturally  energetic  faculties.  Phrenology  will  lead  to  important  con- 
siderations regarding  criminal  punishment,  particularly  in  houses  of 
correction.  It  will  enable  us  to  distinguish,  not  only  between  those 
who  have  naturally  strong  evil  propensities,  from  those  whom  distress 
or  other  contingencies  may  have  hurried  on  to  crime,  but  will  point 
out  the  particular  nature  of  the  evil  propensities  to  be  corrected."  It 
will  also  tend,  he  conceives,  to  establish  important  distinctions  between 
different  kinds  of  insanity,  and  enable  us  to  discover  the  treatment  ap- 
propriate for  the  cure  of  each.  Lastly,  it  may  prepare  the  way  to  a 
radical  improvement  of  the  human  race,  by  pointing  out  those  confor- 
mations of  the  head  which  it  is  desirable  to  eradicate  or  to  perpetuate, 
and  which  should  therefore  be  avoided  or  preferred  in  the  choice  of 
marriages.  "  It  is  certainly  a  pity,"  says  Dr.  Spurzheim,  "  that,  in 
this  respect,  we  take  more  care  of  the  races  of  our  sheep,  pigs,  dogs, 
and  horses,  than  of  our  own  qff'spring." 

Such  is  the  body  of  doctrines,  and  such  the  reasonings  in  their  sup- 
port, which  have  emanated  from  the  school  of  Gall  and  Spurzheim, 
and  which  they  have  dignified  with  the  appellation  of  a  new  science. 
A  host  of  opponents,  as  might  be  expected,  have  arisen  against  a  sys- 
tem so  much  at  variance  with  common  notions,  leading  to  conclusions 
so  remote  from  vulgar  apprehension,  and  admitting  so  easily  of  being 
held  up  to  ridicule  by  partial  or  exaggerated  statements.  We  have 
already  noticed  the  objection  founded  upon  its  supposed  tendency  to 
favour  materialism,  and  shall  pass  over  others  of  a  similar  nature, 
which  proceed  upon  the  presumption  of  a  greater  knowledge  of  the 
laws  of  the  creation  than  we  really  possess,  or  which  are  derived  from 
imperfect  or  mistaken  views  of  the  theory  itself.  We  shall  also  refrain 
from  employing  the  weapons  of  ridicule  against  a  system  so  vulnerable 
to  its  attacks,  and  which  would  have  been  so  capable  of  affording 
Swift  a  new  incident  for  the  history  of  the  philosophers  of  Laputa. 
The  simple  exposition  of  the  sandy  foundation  on  which  it  has  been 


OBJECTIONS    TO    PHRENOLOGY.  483 

built,  of  the  flimsy  materials  of  which  it  has  been  composed,  and  the 
loose  mode  in  which  they  have  been  put  together,  will  snfrice  to  enable 
our  readers  to  form  their  own  conclusions  as  to  the  soundness  and 
solicUty  of  the  edifice. 

It  is,  in  the  first  place,  obvious,  that  nothing  like  direct  proof  has 
been  given  that  the  presence  of  any  particular  part  of  the  brain  is  essen- 
tially necessary  to  the  carrying  on  of  the  operations  of  the  mind.  The 
truth  is,  that  there  is  not  a  single  part  of  the  encephalon,  which  has 
not,  in  one  case  or  other,  been  impaired,  destroyed,  or  found  defective, 
without  any  apparent  change  in  the  sensitive,  intellectual,  or  moral 
faculties.  Haller  has  given  us  a  copious  collection  of  cases,  which 
bear  upon  this  point ;  and  a  similar  catalogue  has  been  made  by  Dr. 
Ferriar,  who,  in  a  paper  in  the  fourth  volume  of  the  ManchestPr 
Transactions,  has  selected  many  of  Haller's  cases,  with  considerable 
additions  from  other  authors.  The  evidence  afforded  from  tiiis  mass 
of  facts,  taken  conjointly,  appears  to  us  to  be  sufficient  to  overturn 
their  fundamental  proposition.  This  evidence  is  not  impeached  by  the 
feeble  attempts  of  Dr.  Spurzheim  to  evade  its  force,  by  a  general  and 
vague  imputation  of  inaccuracy  against  the  observers,  or  by  having 
recourse  to  the  principle  of  the  duplicity  of  each  of  the  cerebral  organs  ; 
a  principle  of  very  dubious  application,  on  a  subject  of  so  much  uncer' 
tainty  as  the  physiology  of  the  brain.  Poor,  indeed,  must  be  his 
resources,  when  we  find  him  resorting  to  the  following  argument,  in 
proof  that  the  brain  is  the  organ  of  thought,  namely,  that  "  every  one 
feels  that  he  thinks  by  means  of  his  brain."  We  doubt  much  if  any 
one  has  naturally  that  feeling. 

It  requires,  also,  but  a  slight  attention  to  perceive,  that  the  very 
ground-work  on  which  the  whole  of  the  subsequent  reasoning  proceeds, 
namely,  that  the  different  faculties  of  the  mind  are  exercised  respec- 
tively by  different  portions  of  the  brain,  is  in  no  resj^ect  whatever 
established.  The  only  arguments  in  its  favour  which  bear  the  least 
plausibility,  are  derived  from  analogy.  Now,  analogy,  in  reasoning 
concerning  the  unknown  operations  of  nature,  is,  at  best,  but  slippery 
ground  ;  and  when  unsupported  by  any  other  kind  of  evidence,  cannot 
lead  to  certain  knowledge,  far  less  constitute  the  basis  of  an  extensive 
system.  The  utility  of  analogical  deductions  as  to  what  takes  place  in 
one  department  of  nature,  from  our  knowledge  of  what  occurs  in 
another,  consists  chiefly  in  their  afl^ording  indications  of  what  may  pos- 
sibly happen,  and  thus  directing  and  stirnulating  our  inquiries  to  the 
discovery  of  truth  by  the  legitimate  road  of  observation  and  experiment. 
But  to  assume  the  existence  of  any  such  analogy  as  equivalent  to  a 
positive  proof,  resulting  from  the  evidence  of  direct  observation,  is  a 
gross  violation  of  logic.  Yet  it  is  upon  assumptions  of  this  kind  that 
Drs.  Gall  and  Spurzheim  have  ventured  to  found  all  the  leading  propO' 
sitions  of  their  doctrine.  In  the  secretions  of  the  body,  they  observe, 
the  preparation  of  different  fluids  is  consigned  to  different  glands,  having 
different  appropriate  structures";  and  they  consider  this  analogy  as  a 
demonstrative  proof  of  what  happens  in  the  operation  of  thought,  and 
the  phenomena  of  the  passions,  which,  because  they  differ  as  much  in 
their  nature  as  milk  does  from  gall,  must,  accordingly,  be  th.e  result  of 


484  APPENDIX. PHRENOLOGY. 

actions  in  different  portions  of  the  brain  ;  which  portions  are,  there- 
fore, to  be  regarded  as  so  many  different  organs,  rather  than  as  parts 
of  one  organ.  Even  in  a  case  where  all  the  analogies  are  favourable 
to  one  side  of  a  question,  such  a  loose  mode  of  reasoning  would  be 
entitled  to  little  confidence  ;  but  how  fallacious  must  it  not  prove,  when 
analogies  can  be  pointed  out  whjch  apply  in  the  opposite  direction  ?  It 
requires  no  extensive  knowledge  of  the  animal  economy  to  perceive, 
that  modifications  of  functions  equally  diversified  with  those  of  the 
'intellect,  are,  in  many  cases,  the  result  ef  actions  taking  place  in  the 
same  organ.  Does  not  the  same  stomach  digest  very  different  and 
even  opposite  kinds  of  aliment  ?  Yet  we  do  not  find  that  one  portion 
of  that  organ  is  destined  for  the  digestion  of  meat,  and  another  for  the 
digestion  of  vegetable  matter  ;  although  the  operations  required  for  the 
conversion  of  such  different  ingredients  into  the  same  chyle,  cannot- 
possibly  be  the  same.  Nerves  perform  the  double  office  of  volition 
and  sensation  ;  but  the  different  bundles  of  fibres  which  convey  each 
impression,  the  one  to  the  muscles,  the  other  to  the  sensorium,  are 
wrapped  up  in  the  same  sheath,  and  are  so  intimately  intermixed  during 
their  course  as  to  constitute  a  single  cord.  The  same  organ  serves  for 
the  hearing  of  acute  and  of  grave  sounds.  The  whole  retina,  and  not 
merely  different  portions  of  its  surface,  receives  the  impression  of  dif- 
ferent kinds  of  colour  ;  there  is  not  one  organ  for  the  perception  of 
blue  and'another  for  the  perception  of  red  rays.  Guided  by  such  ana- 
logies as  these,  might  we  not  be  equally  justified  in  concluding,  that 
the  same  part  of  the  brain  may  serve  for  the  memory  of  words,  as  for 
the  memory  of  things ;  and  the  same  portion  of  that  organ  which  ena- 
bles us  to  conceive  the  idea  of  figure,  may  also  suggest  to  us  that  of 
size  ? 

The  same  doctrine  of  the  plurality  of  cerebral  organs,  is  endeavoured 
to  be  supported  by  another  analogy,  equally  vague  and  loose  with  the 
former,  namely,  that  the  sense  of  fatigue  from  long  continued  muscular 
exertion,  resembles,  in  its  circumstances,  the  effects  of  long  continued 
study  on  the  mind,  and  is  equally  relieved,  in  both  cases,  by  a  change 
of  action.  To  us,  however,  it  appears,  that  this  analogy  might,  with 
equal  justice,  have  been  adduced,  as  favouring  the  opposite  view  of  the 
subject;  for  we  can  just  as  readily  conceive  the  sense  of  fatigue  to  take 
place  from  the  exercise  of  the  whole  organ  in  a  particular  mode,  as 
from  that  of  any  part  of  the  organ ;  and  relief  must  equally,  in  both 
cases,  be  experienced  from  the  ceasing  of  that  action,  or  from  the 
substitution  of  one  of  a  different  kind.  The  muscles  admit  only  of  one 
kind  of  action  ;  and  the  energy  which  each  derives  from  the  nerves, 
when  once  exhausted,  is  not  so  readily  replaced  from  the  general  stock 
belonging  to  the  system.  In  the  finer  textures  of  the  body,  which 
approach  more  to  that  of  the  brain,  the  analogy  not  only  fails  of  giving 
support  to  the  doctrine,  but  has  an  opposite  tendency.  The  same 
retina,  when  fatigued  by  the  continued  impression  of  a  particular  colour, 
is  still  as  ready  as  before  to  receive  the  impression  of  another  colour. 
The  circumstance  of  partial  fatigue  with  regard  to  one  set  of  actions, 
may,  therefore,  exist,  without  implying  the  necessity  of  a  separate 
organ  for  the  performance  of  these  actions.  Indeed,  if  the  brain  have 
any  laws  similar  to  those  of  muscular  motion,  it  must  have  a  much 

I 


PRACTICAL    DIFFICULTIES.  485 

greater  number  peculiar  to  itself,  and  all  such  distant  analogies  as  those 
we  have  been  considering,  must  be  perfectly  inconclusive.  Similar 
observations  will  apply  to  the  explanation  of  the  phenomena  of  sleep, 
of  dreams,  of  somnambulism,  of  partial  losses  of  memory,  and  of 
^insanity.  It  is  equally  conceivable,  that  they  should  result  from  the 
imperfect  or  differently  modified  actions  of  one  organ,  as  from  the 
separate  activity  of  different  parts  of  that  organ,  whilst  the  other  parts 
are  inactive.  Analogies  may  be  equally  adduced  in  support  of  both 
sides  of  the  question,  and  can  certainly  prove  nothing  on  either. 

Dr.  Gall  and  Spurzheim  appeal  with  great  confidence  to  anatomy, 
and  particularly  to  their  own  anatomical  discoveries,  as  affording  a  solid 
support  to  their  doctrines.  "  We  never,"  say  they,  "  separate  anatomy 
from  physiology,  for  physiology  without  anatomy  is  unfounded;  while 
anatomy  without  physiology  is  useless.  A  physiological  system  of 
the  brain  would  necessarily  be  false,  were  it  in  contradiction  with  its 
anatomical  structure."  This  conclusion,  which  at  best  is  but  a  negative 
one,  is  totally  inapplicable  to  the  theories  in  question.  The  anatomy 
of  the  brain  is  so  complex,  and  so  void  of  apparent  adaptation  to  any 
purpose  we  can  understand,  that  it  will  suit  any  physiological  system 
nearly  equally  well ;  at  least  it  can  never  be  adduced  in  contradiction 
of  any  hypothesis,  however  wild,  that  can  be  framed  as  to  the  mutual 
operation  of  soul  and  body.  All  that  these  anatomists  have  done,  in 
this  respect,  is  to  show  that  there  is  no  appearance  of  a  common  centre 
of  departure  or  of  a  collection  of  nervous  filaments.  The  separation  of 
the  parts  of  the  brain  and  their  diversity  of  shape,  can  no  more  be 
evidence  of  a  diversity  in  their  functions,  than  the  multitude  of  distinct 
and  separate  lobules  which  compose  th,e  kidneys  of  birds,  and  of  a 
great  number  of  quadrupeds,  are  indications  that  each  part  performs  a 
different  office.  Comparative  anatomy,  indeed,  upon  which  so  much  is 
made  to  hinge,  is  of  all  guides  the  most  fallible  in  questions  of  this 
nature ;  since  we  behold,  in  numberless  instances,  a  great  variety  of 
ways  in  which  nature  accomplishes  the  same  function  and  the  same 
purpose,  in  different  departments  of  the  animal  creation.  But  on  a 
comparison  of  animals  with  each  other,  it  may  even  be  doubted,  whether 
there  is  any  connexion  or  proportion  observable  between  their  intellect 
or  inclinations  and  the  number  of  parts  in  their  brains. 

The  possibility  of  discovering  the  size  and  the  shape  of  the  different 
parts  of  the  brain  from  the  external  examination  of  the  head,  is  also 
discountenanced  by  anatomy.  There  are  often  considerable  impres- 
sions on  the  interior  of  the  skull,  where  the  corresponding  exterior 
surface  does  not  exhibit  the  slightest  appearance  of  projection,  and  is 
sometimes  even  depressed  ;  and  there  are  frequently  large  prominences 
without,  where  there  are  no  corresponding  concavities  within  ;  so  tliat 
when  the  outer  surface  of  the  bony  case  is  compared  with  a  mould  in 
plaster  or  wax  of  the  cavity  itself,  they  exhibit  considerable  differences, 
and,  from  the  great  variation  which  may  take  place  in  the  thickness  of 
the  bones,  this  difference  is  not  the  same  in  degree  in  any  two  skulls. 

Hollow  as  are  the  foundations  of  this  theory,  the  materials  which 
compose  the  superstructure  will  prove,  on  examination,  to  be  still 
more  frail  and  unsound.     The  whole  fabric  rests  upon  the  validity  of 

41* 


486  APPENDIX. PHRENOLOGV. 

a  single  proposition,  which  in  itself  is  extremely  questionable,  namely, 
that  the  size  of  an  organ  is  in  general  a  criterion  of  the  energy  with 
which  its  function  is  performed.  If  any  doubt  should  remain  as  to  its 
truth,  the  whole  of  the  pretended  discoveries  relative  to  the  functions 
of  the  several  parts  of  the  brain  are  shaken,  and  the  fantastical  edifice 
has  no  auxiliary  prop  to  arrest  its  fall.  So  essentially,  indeed,  does 
the  whole  of  this  system  depend  upon  the  truth  of  a  number  of  inde- 
pendent propositions,  that  if  any  one  of  them  should  turn  out  to  be 
incorrect,  the  whole  fabric  must  give  way.  The  evidence  in  its  favour, 
instead  of  being  cumulative,  is  disjunctive.  Where  each  proposition 
must  be  sustained  by  a  separate  series  of  proofs,  as  is  the  case  here,  it 
is  evident  that  the  chances  of  error  must  be  multiplied  in  proportion  to 
the  number  of  steps  we  must  ascend  before  we  can  arrive  at  the  last 
conclusions.  Let  us,  for  example,  examine  the  logic  by  which  the 
above  fundamental  principle  is  deduced.  "  A  large  muscle,"  say  they, 
"  is  stronger  than  a  small  one  ;  and  a  large  loadstone  is  more  powerful 
in  its  attraction  than  a  smaller  one.  Why  should  it  not  be  the  same 
with  regard  to  the  brain  ?"  Thus  again  do  they  confide  in  a  loose 
analogy,  derived  from  another  and  a  totally  different  part  of  the  econo- 
my ;  and  as  if  the  organization  and  functions  of  the  animal  body  were 
not  sufficiently  remote  from  the  nature  and  operations  of  the  human 
mind,  the  inanimate  world, is  ransacked  for  the  shadows  of  an  analogy, 
which,  when  viewed  through  such  a  distance  of  intervening  mist,  may 
wear  the  semblance  of  reality.  But  the  phantom  must  immediately 
vanish  upon  a  near  inspection.  For  the  perfection  of  a  refined  and 
delicate  instrument,  such  as  must  be  that  which  is  subservient  to  the 
operations  of  the  intellect,  innumerable  conditions  must  concur; 
amongst  which  that  of  size,  it  is  reasonable  to  suppose,  is  the  least 
important.  Delicacy  of  texture,  fineness  of  organization,  and  harmony 
of  adjustment  between  the  several  parts  of  its  complex  structure,  must 
contribute  infinitely  more  towards  rendering  it  capable  of  perfoi;ming 
its  office,  than  superior  magnitude ;  a  circumstance  which  in  itself  is 
quite  as  likely  to  prove  a  source  of  imperfection,  as  to  impart  additional 
facility.  Increase  of  size  in  the  viscera  of  the  body  is  often  the  indi- 
cation of  a  diseased,  instead  of  a  healthy  state.  Small  eyes.  Professor 
Hufeland  observes,  see  with  more  strength,  and  last  longer  than  large 
eyes.  Why  may  not  this  be  also  the  case  with  the  organs  of  the 
brain  ?  But  really,  in  our  present  state  of  ignorance  as  to  the  mode  of 
operation  by  which  they  are  subservient  to  the  processes  of  intellect 
and  sensation,  all  such  reasonings  «  priori  on  their  functions,  as  con- 
nected with  their  size,  must  be  completely  illusory. 

Even  were  we  to  admit  so  questionable  a  doctrine  as  that  the  ener?- 
gies  of  the  parts  of  the  brain  are  proportional  to  their  magnitude, 
insuperable  difficulties  would  still  be  opposed  to  the  determination  of 
their  relative  size,  in  the  living  head  ;  crowded  as  all  these  organs  are 
in  a  narrow  compass  and  completely  hid  from  our  view  by  an  irregular 
bony  case  which  protects  them  from  injury,  and  which  is  itself 
covered  by  a  thick  and  variable  layer  of  muscle  and  integument.  Let 
us,  however,  for  the  sake  of  argument,  suppose  that  the  form  of  each 
organ  within  the  skull  can  really  be  ascertained  by  external  examina- 


PRACTICAL    DIFFICULTIES.  487 

tion  of  the  head ;  shall  we  allow  it  to  be  an  easy  task  to  determine  the 
real  character  of  the  individual  who  is  the  subject  of  observation? 
Are  we  always  able  to  discriminate  between  real  and  affected  senti- 
ment ;  or  to  mark  with  certainty  the  operation  of  all  the  various  motives 
which  constitute  the  springs  of  action  ?  Is  the  transient  glance  of  a 
passing  observer  sufficient  for  unravelling  the  complex  web  of  our 
affections,  or  unveiling  the  secret  and  tortuous  recesses  of  the  human 
heart,  so  as  to  assign  to  each  principle  its  precise  sphere  of  agency  ? 
Can  the  most  profound  moralist,  or  acute  metaphysician  pronounce 
with  confidence  what  are  the  natural  dispositions  of  any  human  beiil^, 
knowing,  as  we  do,  that  these  dispositions  must  have  been  changed 
or  modified,  exalted  or  subdued,  perverted  or  refined,  by  the  force  of 
habit,  education,  example,  and  a  multitude  of  other  powerful  causes, 
which,  in  his  progress  through  life,  have  moulded  his  intellectual  and 
moral  constitution  ?  Can  he  trace  them  through  the  guise  of  falsehood, 
artifice,  and  dissimulation,  which  so  commonly  hide  his  real  character 
from  the  world,  and  which  occasionally  deceive  the  eye  of  the  closest 
and  most  vigilant  observer  ?  Is  it  to  the  behaviour  of  a  person  who 
knows  that  he  is  watched  ;  is  it  to  the  partial  report  of  his  friends ;  is 
it  to  the  testimony  of  the  individual  himself,  the  most  fallible  of  all, 
that  the  phrenologist  is  to  trust  for  his  knowledge  of  human  character  ? 
Such,  however,  is  the  kind  of  experience,  from  which  it  appears  that  all 
the  doctrines  relative  to  the  functions  of  the  difTerent  parts  of  the  brain 
have  been  derived  ;  and  it  is  in  this  experience,  as  in  an  impregnable 
fortress,  that  the  adherents  of  the  system  make  their  last  and  most 
resolute  stand.  Quitting  the  airy  region  of  theory,  they  fancy  them- 
selves posted  upon  a  rock,  secure  against  the  insiduous  minings  of 
scepticism,  and  bidding  defiance  to  the  rude  assaults  of  argument.  The 
appeal  to  the  evidence  of  induction,  as  to  the  supreme  authority  in  the 
court  of  philosophy,  is  made  with  confidence  ;  and  all  the  wild  effusions 
of  a  bewildered  fancy  are  presumed  to  be  sanctioned  by  a  supposed 
conformity  with  experience.  You  may  speculate  or  reason,  they  ex- 
(?laim,  as  you  please  ;  observation  shows  that  such  and  such  forms  of 
the  head,  are  the  invariable  concomitants  of  such  and  such  predominant 
dispositions  and  faculties.  Who  will  dare  to  set  up  his  opinion  in 
opposition  to  ascertained  facts  ?  We  venture  only  to  express  strong 
doubts  as  to  the  reality  of  these  facts,  on  which  so  much  is  made  to 
depend,  possessing  the  character  of  general  facts.,  that  is,  of  being  the 
results  of  legitimate  induction  ;  and  to  suggest  the  expediency,  pre- 
viously to  any  admission  of  their  truth,  of  inquiring  not  only  into  the 
manner  in  which  the  knowledge  of  these  pretended  facts  has  been 
obtained,  and  in  Avhich  induction  from  them  have  been  made,  but  also 
into  the  talents  and  qualifications  of  the  observer  upon  whose  testimony 
we  receive  them  for  the  exercise  of  this  philosophical  process.  We 
should  know  in  what  spirit  he  conducted  the  inquiry  ;  with  what  pre- 
vious dispositions  he  examined  the  objects  of  his  contemplation  ;  what 
motives  led  him  to  these  researches  ;  and  what  interest  he  i^ay  have 
in  the  event.  Experience,  we  should  recollect,  leads  to  very  dififerent 
results,  according  to  the  sagacity  and  good  faith  of  the  person  who 
acquires  it.     Minds  already  prejudiced  collect  from  it  only  a  confirma- 


488  ,  APPENDIX. PHRENOLOGY. 

tion  of  their  errors,  and  become,  by  its  means,  only  the  more  obsti- 
nately wedded  to  their  opinions.  The  sailor,  steadfast  in  his  belief  that 
his  whistling  to  the  sea  will  raise  a  wind,  or  conjure  up  a  storm,  instead 
of  being  undeceived  by  experience  is  only  the  more  strengthened  in  his 
faith  by  the  observations  which  it  furnishes  to  him.  In  what  a  multi- 
tude of  instances  do  we  not  find  men  deceiving  themselves  as  grossly, 
when  they  draw  inferences  from  what  they  see,  if  prepossessed  with 
the  expectation  of  meeting  with  a  certain  coincidence,  or  succession  of 
events.  How  disposed  are  we  all  to  disregard  the  exceptions  to  a 
prtconceived  rule,  and  to  allow  undue  weight  to  every  example  that 
conforms  to  it.  How  willingly  we  repel  the  evidence  that  opposes, 
and  how  eagerly  we  catch  at  whatever  corroborates  our  previous  notions, 
especially  when  those  notions  have  originated  with  ourselves,  and  are 
viewed  as  the  darling  offsprings  of  our  own  lucubrations. 

The  discerning  reader  may  already  have  perceived  strong  indications 
of  this  bias  in  the  framers  of  the  phrenological  system,  from  the 
account  we  have  already  given  of  its  origin  and  history,  and  of  the 
kind  of  evidence  on  which  they  pretend  to  establish  its  doctrines.  In 
order,  however,  to  enable  him  to  form  a  correct  idea  of  the  species  of 
logic  which  they  have  been  in  the  habit  of  employing,  and  which  they 
deem  conclusive,  and  of  the  tone  of  mind  with  which  they  prosecute 
the  investigation  of  subjects  where  nothing  but  the  exercise  of  consum- 
mate prudence  can  secure  from  error,  we  shall  conclude  by  offering 
one  or  two  specimens  of  their  mode  of  reasoning.  We  shall  pass  over 
the  numerous  stories,  each  more  ridiculous  than  the  preceding,  of  irre- 
sistible natural  inclinations  to  wander  from  place  to  place,  to  commit 
murder,  theft,  infanticide,  and  other  crimes,  without  any  assignable 
object.  We  shall  refrain  from  criticising  the  wonderful  accounts  of 
people  who  were  insane  on  one  side  of  the  head  only,  and  observed 
their  insanity  with  the  other  side,  and  of  others  who  heard  angels  sing, 
and  devils  roar,  only  on  one  side;  nor  shall  we  stop  to  investigate  the 
curious  case  of  the  woman  who  declared  in  a  court  of  justice,  when 
accused  of  having  destroyed  her  infant,  that  her  sole  motive  for  becom- 
ing pregnant  was  that  she  might  enjoy  the  exquisite  pleasure  of  killing 
her  own  child.  .  Neither  shall  we  venture  to  involve  ourselves  in  that 
metaphysical  labyrinth  of  the  thirty-Jive  special  faculties  into  which 
they  pretend  to  have  analyzed  the  hurgan  soul  ;  but  content  ourselves 
with  examining,  what  in  fact  alone  deserves  examination,  the  sort  of 
evidence  brought  forward  to  establish  the  relation  between  each  faculty 
and  a  particular  defined  portion  of  the  brain.  .We  shall  take,  for  this 
purpose,  the  following  passage,  which  may  be  esteemed  a  fair  specimen 
of  the  whole. 

"  Dr.  Gall  examined  the  head  of  a  woman  at  Vienna  who  was  known 
as  a  model  of  friendship.  She  suffered  different  changes  of  fortune  ; 
she  became  alternately  rich  and  poor  ;  but  was  attached  to  her  former 
friends.  Gall  found  the  part  of  her  head  situated  upward  and  outward 
from  the  organ  of  philoprogenitiveness,  very  prominent,  and  called  it 
the  organ  of  friendship.  Our  observations  are  not  multiplied  enough 
to  enable  us  to  decide  positively  on  this  organ  ;  yet  its  seat  appears  to 
be  more  than  probable.     It  must  be  inferiorly,  because  this  faculty 


REASONING    EMPLOYFJD    BY    PHRENOLOGY.  489 

exists  in  the  lower  animals,  and  is  a  propensity.  For  this  reason  it 
belongs  to  their  region  of  the  head  ;  and  according  to  its  mimical  signs, 
and  the  motions  of  the  head  when  it  is  aetive,  it  lies  laterally  and 
backward."  Dr.  Spurzheim,  it  is  obvious,  here  reasons  in  a  circle; 
for  he  assumes  as  true  the  thing  to  be  proved,  namely,  that  faculties  of 
a  certain  class  reside  in  a  certain  department  of  the  head,  and  then 
applies  it  to  establish  the  very  proof  on  which  the  proposition  itself 
ouglit  to  have  rested.  In  order  to  render  intelligible  the  latter  part  of 
his  argument,  the  reader  should  be  informed  that  Drs.  Gall  and  Spurz- 
heim believe,  that,  when  any  faculty  of  the  mind  is  strongly  excited,  the 
action  of  the  corresponding  organ  in  the  brain  tends  to  raise  that  part  . 
of  the  head  in  which  it  is  situated  ;  so  that  the  person  has  a  propensity 
to  lay  his  finger  upon  the  nearest  external  part  of  the  head,  or  some- 
times to  apply  his  hand  to  it,  either  to  cool  it  when  too  hot,  or  to 
warm  it  when  too  cold,  and  that  he  is  occasionally  prompted  to  rub  it 
in  order  to  excite  it  when  too  sluggish.  Thus,  when  we  endeavour  to 
recollect  a  name  or  a  word,  we  unconsciously  slap  our  foreheads,  or 
rub  the  skin  a  little  above  the  eyes,  or  perhaps  higher  still,  just  where 
the  appropriate  organ  of  memory  is  situated,  that  it  may  awake  and 
exercise  its  peculiar  faculty.  When  embarrassed  by  any  difficulty,  we 
gently  stimulate  in  like  manner,  the  organ  of  contrivance,  by  scratching 
the  head  at  the  part  under  which  is  the  seat  of  constriictiveness.  The 
timid  man  scratches  his  head  on  the  organ  of  courage  behind  his  ear, 
as  if  he  tried  to  rouse  the  feeble  organ  into  activity.  A  proud  man 
holds  his  head  erect  upon  his  shoulders,  and  raises  himself  upon  his 
toes,  for  no  other  reason  than  because  the  organ  of  the  sentiment  lies  at 
the  very  top  of  the  head,  and  is  therefore  elevated  by  the  action.  A 
sense  of  danger,  or  the  necessity  of  circurnspection,  leads  all  animals, 
man  not  excepted,  to  stretch  their  necks  forwards  horizontally,  thus 
presenting  the  broad  extent  of  that  organ,  as  it  were,  in  front.  Devo- 
tion raises  the  head  gently  ;  and  our  adorations  are  all  directed  up- 
wards, not  because  we  regard  ihe  Deity  as  above,  but  because  the 
organ  of  adoration  is  situated  in  the  centre  of  the  upper  part  of  the 
head.  When  busied  in  deep  contemplation,  we  cover  the  whole  fore- 
head with  our  hands,  as.it  is  'there  that  the  reflecting  faculties  are 
lodged  ;  and,  accordingly,  when  we  reproach  any  one  for  his  want  of 
reflection,  we  put  our  hand  to  this  part  of  the  head ;  and  exclaim, 
"  he  wants  it  here."  If  we  try  to  recollect  a  date,  we  put  into  action 
the  organ  of  time,  which  being  situated  over  the  eyebrows,  and  a  little 
to  one  side,  occasions  an  involuntary  movement  of  the  eyes  upwards 
and  towards  the  temples.  In  beating  time  to  a  musical  air,  we  make 
the  head  oscillate  from  side  to  side,  because  the  organs  of  tone  as  well 
as  of  time,  being  situated  on  each  side,  and  being  alternately  in  action, 
occasion  these  gesticulations.  Sterne  excelled  in  wit :  and  we  find 
him  represented  in  all  his  portraits  with  his  head  leaning  on  his  hand, 
the  fore-fing;er  of  which  is  placed  on  a  particular  part  of  the  forehead. 
Dr.  Spurzheim  considers  this  as  one  of  the  proofs  that  the  organ  of  wit 
occupies  that  very  spot. 

With  minds  capable  of  allowing  any  weight  to  such  observations, 
and  imbued  with  such  notions  of  the  nature  of  philosophical  inductions, 


490 


APPENDIX. PHRENOLOGY. 


as  are  implied  by  the  grave  admission  of  such  frivolous  arguments  as 
these,  the  investigation  of  the  laws  of  nature  must  be  an  easy  and  a 
delightful  task.  With  the  abundant  and  all-povs^erful  resources,  which 
their  indulgent  method  of  reasoning  is  ever  ready  to  supply,  all  diffi- 
culties may  be  smoothed  away,  all  chasms  immediately  filled  up,  and 
all  obstacles  made  to  vanish  the  moment  they  arise.  We  need  not  be 
under  any  embarrassment  at  meeting  with  "a  skull  exhibiting  a  particu- 
lar prominence,  although  the  faculty  which  should  correspond  to  it  be 
deficient.  Doubtless  the  individual  must  have  been  strongly  gifted  by 
nature  with  this  faculty,  but  education  has  long  ago  taught  him  to  dis- 
guise or  suppress  its  manifestations.  It  exists,  perhaps,  unknown  to 
the  person  himself,  and  wants  only  a  proper  occasion  for  its  being  ex- 
hibited ;  or  more  probably  the  other  faculties,  having  received  a  greater 
proportional  development,  have  overpowered  and  prevented  it  from 
appearing.  If  we  find,  on  the  contrary,  a  strongly  marked  faculty, 
without  the  corresponding  shape  of  the  head,  we  may  still  conclude 
that  the  organ  exists  notwithstanding  ;  for  the  neighbouring  organs, 
having  received  a  greater  extension,  may  have  pushed  it  from  its  true 
place,  or  have  grown  up  around  it,  and  have  concealed  it  from  vulgar 
observation.  Its  not  having  been  recognised  is  only  a  proof  of  want 
of  skill  in  the  observer  ;  no  doubt,  it  would  easily  have  been  discovered 
by  the  eye  or  hand  of  a  true  believer,  and  experienced  cranioscopist ; 
for  it  should  be  recollected  that  the  differences  are  often  very  minute, 
and  require  the  tactus  eruditus  for  their  detection.  Besides,  how  can 
we  be  certain  that  the  excellence  of  the  faculty  in  question  is  not  of  an 
artificial  or  relative  kind,  and  that  it  results  from  education,  or  the 
weakness  of  opposite  faculties,  rather  than  from  nature  ?  If  all  these 
expedients  should  fail  us,  we  have  nothing  to  do  but  to  plunge  into  the 
depths  of  metaphysics,  to  refine  and  make  subtle  distinctions,  or  loosen 
the  signification  of  a  few  words,  till  we  have  entangled  ourselves  in  a 
wood,  and  lost  sight  of  the  real  difficulty  that  had  perplexed  us.  Thus 
will  the  theory  be  freed  from  all  exceptions,  and  the  induction  be  ren- 
dered complete.  With  such  a  convenient  logic,  and  accommodating 
principles  of  philosophizing,  it  would  be  easy  to  prove  any  thing. 
We  suspect,  however,  that  on  that  very  account,  they  will  be  rejected 
as  having  proved  nothing. 


We  have  here  re-printed  the  Essa.y  on  this  subject  which  originally 
appeared  under  the  head  of  Cranioscopy,  in  the  Supplement  to  the 
Sixth  Edition  of  the  Encyclopaedia  Britannica.  We  have  done  so  be- 
cause we  have  not  seen  any  reason  to  alter  our  views.  Since  the  year 
1818,  when  that  essay  was  written,  replies  have  been  attempted  to 
some  of  our  strictures  ;  particularly  by  Mr.  George  Combe,  in  his 
'■^Essays  on  Phrenology,  and  on  the  objections  made  against  it,''^ 
Edinburgh,  1819;  and  by  Dr.  Andrew  Combe,  in  \\\e  Phrenological 
Journal.  Although  the  conductors  of  this  Journal  have  admitted  that 
our  Article  was  "  regarded  in  the  South  as  the  most  formidable  attack 


REPLY   TO   CRITICISMS.  491 

Phrenology  ever  had*to  sustain,"*  and  have  in  so  far  paid  lis  a  com- 
pliment, we  deem  it  unnecessary  to  answer,  otherwise  than  very 
generally,  their  comments  on  the  reasonings  contained  in  it ;  because 
most  of  those  comments  are  founded  on  a  misconception  of  the  scope 
of  our  arguments.  When,  for  instance,  we  attempted  to  show,  that, 
in  establishing  a  philosophical  principle,  mere  analogies  ought  not  to 
be  esteemed  as  equivalent  to  proofs,  and  when  we  maintained  that  they 
are  still  less  to  be  relied  on,  when  other  analogies,  of  a  contrary  ten- 
dency, can  be  adduced  on  the  other  side  of  the  question,  we  are  re- 
presented by  Dr.  Combe  as  building  our  arguments  on  analogy,  the 
very  principle  of  which  we  were  pointing  out  the  fallacy,  and  repu- 
diating the  authority ;  and  we  are  even  charged  with  being  guilty  of 
the  strange  inconsistency  of  endeavouring  to  "  refute  direct  inductive 
evidence,  by  that  drawn  from  analogy."t  Any  reader  who  had  paid 
the  least  attention  to  the  train  of  reasoning  we  employed,  must  have 
perceived  that  our  reasoning  was  diametrically  the  reverse  of  that 
which  is  imputed  to  us  ;  and  that  we  had  even  guarded  against  the 
possibility  of  mistake  by  the  sentence  concluding  with  the   words, 

"  all  such  reasonings  a  priori must  be  completely  illusory." 

By  the  help  of  a  mis-quotation,  in  which  the  qualifying  adverb 
"  nearly"  is  omitted,  we  are  represented  as  having  asserted  that  the 
anatomy  of  the  brain  "  will  suit  any  physiological  system  equally 
well. "J  All  the  notions  we  can  form  of  the  nature  of  mental  opera- 
tions are  so  completely  and  essentially  different  from  any  of  the  affec- 
tions of  which  we  can  conceive  matter  to  be  capable,  that  it  is  utterly 
impossible  for  us  to  understand  the  mode  in  which  a  connexion  has  been 
established  between  them  ;  or  to  imagine  any  physical  structure  what- 
soever, which  shall,  in  the  remotest  manner,  correspond  with  the  meta- 
physical constitution  of  the  soul.  This,  however,  we  may  confidently 
assert,  that  amongst  all  the  hypotheses  which  have  been  propounded 
respecting  the  correspondence  between  the  corporeal  instruments  of  the 
mind,  and  the  mental  faculties  themselves,  the  one  which  is  the  least  in 
accordance  with  the  actual  structure  of  the  brain,  is  that  devised  by  the 
phrenologists.  Let  a  person,  unacquainted  with  the  anatomy  of  that 
organ,  be  shown  the  phrenological  map  of  the  cerebral  regions,  and 
let  him  be  told,  that  to  each  corresponding  subjacent  portion  of  the  brain 
is  ascribed,  as  to  a  separate  organ,  a  certain  special  mental  function  ; 
one  set  of  these  organs  being  appropriated  to  the  establishment  of 
certain  definite  propensities,  whilst  another  set  gives  rise  respectively 
to  various  sentiments,  and  a  third  confers  on  each  its  peculiar  intellectual 
power;  with  what  immeasurable  surprise,  on  lifting  up  the  bony 
covering  which  had  concealed  this  expected  assemblage  of  well  defined 
organs,  would  he  behold  a  uniform  mass  of  pulpy  substance,  divided 
by  furrows  only,  into  serpentine  but  continuous  convolutions,  bearing 
no  conformity  or  even  similitude  to  the  notions  which  his  previous 
instructions  had  led  him  to  form  of  distinct  masses,  divided  from  each 
other  in  accordance  with  their  phrenological  functions.'  Each  of  these 
pretended  organs,  far  from  being  isolated  in  its  structure,  as  its  alleged 

*  PhrenoIogicalJoumal,  i.  166.  f  lb.  i,  168,  169.  i:  lb.  366. 


492  APPENDIX. PHRENOLOGY. 

isolated  functions  would  imply,  from  the  neighb(#iiring  parts,  is  seen  to 
pass  on,  without  visible  boundary,  to  the  next,  by  a  continuity  of 
cerebral  substance.  Turning  round  upon  his  instructor,  would  he  not 
complain  of  being  misled  by  him  ;  and  would  he  not  require  him  to 
explain  what  intermediate  function  he  can  ascribe  to  those  portions  of 
the  same  convolution  which  occijpy  an  intermediate  place  between  two 
organs,  to  which  he  has  already  assigned  functions  utterly  heterogeneous 
with  one  another?  What  lucid  ideas  can  he  convey  of  a  function 
intermediate  between  benevolence  and  imitation,  between  ideality  and 
acquisitiveness,  between  cautiousness  and  adhesiveness,  or  between 
self-esteem  and  concentrativeness  or  inhabitiveness,  of  which  the 
respective  organs  are  not  merely  contiguous,  but  pass  insensibly  into 
one  another  ;  and  what  is  the  curious  and  hitherto  nondescript  office 
that  he  will  assign  to  those  portions  of  the  brain  which  occupy  the 
central  space  at  the  junction  of  quintuple  groups  of  organs,  such  as 
those  of  ideality,  acquisitiveness,  constructiveness,  tune,  and  wit,  all 
of  which,  though  separated  by  the  fancy  of  the  phrenologist,  have  been 
by  nature  amalgamated  into  one  continuous  mass,  undistinguishable  by 
any  visible  lines  of  demarcation  ? 

Not  content  with  expressing  his   dissatisfaction  at  our  failing  to 
perceive  the  accordance  between  the  structure  Of  the  human  brain  and 
the  doctrines  of  phrenology,  Dr.  Combe  extends  his  censure  to  our 
objection  as  to  the  evidence  which  observations  on  lower  animals  are 
supposed  to  afford  in  their  favour ;  and  to  our  assertion,  that  in  the 
construction  of  their  system  "  much  was  made  to  hinge"  on  facts  derived 
from  compjtfalive  anatomy.     That  the  founders  of  the  system  placed 
great  reliance  on  this  kind  of  evidence,  is  a  proposition  sufficiently  borne 
out  by  the  testimony  of  Sir  George  Mackenzie,  who,  when  speaking 
of  inhabitiveness,  remarks,  "it  is  chiefly  from  observation  on  the  lower 
animals  that  Dr.  Spurzheim  seems  to  consider  it  as  certain,  that  there 
is  such  a  faculty  in  man."*     The  fallacy  of  the  reasoning  by  which 
comparative  anatomy  has  been  pressed  into  the  service  of  phrenology, 
has  been  so  ably  exposed  by  Dr.  Prichard,  in  his  Treatise  on  Insanity, 
that  we  shall  beg  leave  to  borrow  from  that  work  the  following  judicious 
■  remarks.     "The  chief  peculiarity,"  observes  Dr.  Prichard,  "of  Dr. 
Gall's  psychological  theory,  was  the  attempt  to  draw  a  parallel  between 
the  animal  qualities  displayed  by  the  lower  animals  and  the  individual 
varieties  discovered  among  men."     He  proceeded  "  on  the  principle, 
that  the  innate  or  original  faculties  are  common  to  man  and  the  lower 
tribes  of  animals,  to  those  at  least  which  bear  to  man  a  general  analogy 
in  their  organization,  and  especially  in  the  structure  of  their  nervous 
system ;  and  sought  for  analogies  in  physical  phenomena  between  the 
brute  tribes,  tracing  in  them  the  rudiments  of  those  properties  which, 
taken  collectively,  and  in  their  highest  degree  of  development,  form 
the  human  character,  and  which,  in  lower  degrees  and  various  relations, 
constitute  the  distinctive  nature  of  each  of  the  inferior  kinds.     The 
attempt  was  ingenious,  and  seemed  to  hold  out  the  prospect  of  dis- 
covering curious  and  interesting  relations  ;  but  it  is  necessary,  before 

*  Illustrations  of  Phrenology,  p.  92. 


REPLY    TO    CRITICISMS.  493 

embarking  in  the  inquiry,  to  determine  whether  the  analogies  are  real 
or  apparent ;  for  it  has  been  tacitly  assumed  that  the  supposed  distinc- 
tion between  instinct  and  reason  is  unreal,  and  that  the  active  principles 
are  of  the  same  kind  in  the  higher  and  lower  beings  of  the  creation." 
"  Perhaps  metaphysical  writers  have  been  mistaken  in  laying  down 
so  broad  a  line  of  difference  as  they  have  established.  We  must,  then, 
either  elevate  the  brutes,  or  lower  the  superiority  of  mankind.  Shall 
we  say,  after  tracing  the  operations  of  a  constructive  instinct  so 
wonderfully  displayed  by  the  beaver,  or  in  the  cells  in  which  the  bee 
lays  up  his  honey,  that  an  impulse  to  action  precisely  similar  gave 
origin  to  the  pyramids  of  Egypt,  or  to  the  building  of  Constantinople? 
Shall  we  venture  to  affirm  that  the  tunnel  under  the  Thames  owes  its 
existence  to  a  burrowing  propensity  resembling  that  of  the  rabbit  or 
the  mole  ?  Shall  we  conclude  that  Parry  and  Franklin  sought  the 
regions  of  the  north,  impelled  by  the  instinct  of  the  migratory  rat ;  and 
that  Magellan  and  De  Gama  traversed  the  Southern  Oceans  directed 
by  an  influence  analogous  to  that  which  moves  the  flight  of  swallows? 
Or  may  we,  with  greater  probability,  determine  that  the  lower  tribes 
act  under  the  guidance,  not  of  blind  instinct,  but  of  enlightened  reason ; 
that  metaphysicians  were  mistaken  when  they  laid  down  the  principle, 
'  Deus  est  anima  brutorum,'  that  the  birds  of  passage  have  some  ac- 
quaintance with  physical  geography,  and  know  the  quarter  where 
tropical  warmth  exists  and  'genial  breezes  blow ;  that  the  bee  has 
studied  the  exact  sciences,  and  knows  by  calculation  the  form  most 
advisable  for  its  cells  ?  In  short,  that  there  is  a  real  analogy  and  cor- 
respondence between  the  mental  faculties  of  man  and  the  physical 
endowments  of  those  creatures  whom  he  conceitedly  regards  as  his 
inferiors  ?  If  either  of  these  positions  can  be  maintained,  there  will 
be  a  sound  foundation  for  the  comparative  psychology  of  Dr.  Gall  and 
his  followers  ;  but  if  they  should  be  rejected  as  improbable,  we  must 
admit  that  the  analogies  pointed  out  are  remote,  the  things  compared 
are  diff"erent  in  kind,  they  agree  only  in  external  appearances;  and  we 
shall  be  brought  to  the  conclusion  that  it  has  pleased  the  Author  of 
nature  to  bring  about  corresponding  results  in  the  rational  and  irrational 
departments  of  the  creation,  by  very  different  means." 

"  If  the  evidence,"  continues  Dr.  Prichard,  "  brought  in  support  of 
the  organological  system  depends  so  entirely  on  universal  coincidence 
between  psychical  properties  and  corresponding  varieties  in  the  struc- 
ture of  the  nervous  fabric,  it  must  be  important  to  determine  whether 
there  are  any  departments  of  the  animal  kingdom  in  which  instincts 
and  motive  habitudes,  and  an  entire  psychical  nature  are  displayed 
analogous  to  those  of  vertebrated  animals,  while  yet  in  these  depart- 
ments there  is  no  structure  which  can  be  said  to  bear  resemblance  to 
the  complicated  cerebral  system  of  the  so  termed  higher  animals.  In 
all  the  vertebrated  kinds,  the  organization  of  the  nervous  fabric  is  in 
one  principle,  and  the  same  fundamental  type,  with  diff'erent  degrees 
of  development,  is  traced  in  man  and  all  other  mammifers,  in  birds, 
reptiles,  and  fishes ;  but  here  the  resemblance  terminates,  and  the 
nervous  system  of  molluscous  animals  and  insects  presented  but  few 

42 


494  APPENDIX. PHRENOLOGY. 

and  remote  analogies  to  that  which  belongs  to  the  first  great  branch  of 
the  animal  creation.  It  is,  indeed,  to  be  presumed  that  the  nervous 
system,  taken  as  a  whole,  fulfils,  in  the  tribes  last  mentioned,  the  same 
offices  as  in  those  animals  who  have  it  enclosed  in  a  bony  case.  Still, 
nothing  exists  at  all  resembling  the  complicated  formation  of  a  brain, 
with  its  lobes  and  convolutions.  It  is  so  much  the  more  surprising 
to  find  the  higher  instincts,  which  had  almost  disappeared  in  fishes, 
display  themselves  with  new  splendour  and  variety  in  the  brainless 
insects  ;  creatures  which,  in  the  wonderful  imitations  of  intelligence 
that  govern  their  motive  habits,  rival,  if  they  do  not  even  exceed,  the 
sagacity  of  the  animals  wfeich  most  approximate  to  man." 

"  Now,  if  it  should  be  established,  that  all  those  properties  of  animal 
life,  approximating  to  intelligence,  or  bearing  analogies  so  striking  to 
the  manifestations  of  mind,  which,  in  one  great  division  of  the  animal 
kingdom  are  assumed  to  be  essentially  connected  with,  and  depending 
on,  a  particular  system  of  organization,  exist  in  another  department, 
and  display  themselves  in  all  the  same  various  profusion,  while  the 
creatures  belonging  to  this  latter  department  are  yet  destitute  of  that 
sytem  of  organization,  and  of  any  thing  that  bears  the  resemblance  to 
■  it,  the  advocates  of  Phrenology  will  be  obliged  to  abandon  that  broad 
ground  on  which  they  have  attempted  to  fortify  their  position.  Within 
the  more  confined  field  which  the  vertebrated  tribes  alone  present,  it 
will  be  more  easy  to  maintain  such  an  assumed  connexion  of  physical 
properties  with  a  peculiar  structure ;  or,  rather,  it  is  more  difficult  to 
disprove  it  when   assumed.      The   general  analogy   which   prevails 
throughout  these  tribes  in  the  organization  of  their  cerebral  and  nervous 
system,  affords  no  room  for  so  decisive  a  contradiction  to  the  relation 
which  the  phrenologists  would  establish.     Yet  even  within  this  field 
great  and  striking  facts  display  themselves  which  are  adverse  to  the 
hypothesis.     Birds  and  reptiles,  as  Jacobi  has  observed,  are  nearly,  if 
not  wholly  destitute  of  many  cerebral  parts,  which  in  mammifers  are 
held  as  of  high  importance  for  the  manifestation  of  psychical  proper- 
ties, and  yet  they  display  psychical  phenomena  similar  to  those  of 
mammifers.     Whenever  an  undoubted  and  tangible  fact  be  laid  hold 
of  in  the  diff'erent  proportional  development  of  cerebral  parts,  which 
can  be  brought  into  comparison  with  the  relative  diff"erences  of  animal 
instinct,  or  of  psychical  properties  in  general,  there  is,  if  I  am  not 
mistaken,  a  manifest  failure  of  correspondence  between  the  two  series 
of  observations.     This   has  been  shown  by  Rudolphi  in  a  striking 
manner,  with  respect  to  the  cerebellum.  The  cerebellum,  as  this  writer 
has  observed,  is  found  to  lessen  in  its  proportional  development  as  we 
descend  in  the  scale  of  organized  beings,  without  any  corresponding 
diminution,  and  even  with  an  increase  of  the.  propensity  which  Gall 
connects  with  it.     How  remarkably  powerful  is  this  instinct  in  birds  ; 
and  yet  how  small  is  the  cerebellum  in  the  feathered  tribes  compared 
with  its  size  in  mammifers,  and  even  in  the  latter,  when  we  consider 
the  magnitude  which  it  attains  in  the  human  species  ?     We  observe 
those  tribes  in  which  the  cerebellum  nearly  or  entirely  ceases  to  exist, 
obeying,  nevertheless,  the  impulsion  of  instinct  as  blindly  or  devotedly 


TESTIMONY   ADVERSE    TO    PHRENOLOGY.  495 

as  other  kinds  which  have  the  organ  in  question  remarkably  developed. 
When  we  consider  the  great  amplitude  which  the  cerebellum  attains 
in  man,  in  comparison  with  its  size  in  lower  animals,  we  are  obliged, 
if  we  really  attach  any  importance  to  such  a  system  of  correspondence, 
to  acknowledge  some  relation  between  this  circumstance  and  the 
transcendant  superiority  of  the  human  intellect,  compared  with  the 
psychical  powers  of  brutes." 

"•  The  facts  which  suggest  themselves  as  we  follow  these  trains  of 
reflection,  are  scarcely  to  be  reconciled  with  the  phrenological  theory: 
they  seem,  in  the  first  place,  to  show,  that  the  relations  which  in  it 
are  assumed  to  prevail  through  all  nature  are  subject  to  vast  exceptions  ; 
and  as  one  great  proof  of  the  doctrine  is  the  assumed  universality  of 
such  relations,  or  the  endowment  of  psychial  properties  in  co-extension 
with  certain  peculiarities  of  structure  in  cerebral  parts,  the  exceptions 
endanger  at  least  the  outworks  of  the  whole  doctrine.  When,  in  a 
mpre  limited  survey,  we  confine  our  observation  to  the  sphere  of  verte- 
brated  animals,  and  discover  that  variations  in  psychical  phenomena  take 
place  without  any  evidence  of  corresponding  changes  in  the  structure 
of  cerebral  parts^  and  that  these  changes,  on  the  other  hand,  occur 
without  such  alterations  as  we  are  led  to  anticipate  in  psychical  pro- 
perties, the  system  of  organology  seems  to  be  shaken  to  its  very 
cejitre."* 

Whilst  the  defenders  of  phrenology  have,  on  the  one  hand,  misre- 
presented the  minor  points  of  our  argument,  they  have,  on  the  other, 
disguised  from  their  readers  that  it  is  on  the  insufficiency  of  the  evi- 
dence adduced  in  support  of  their  doctrine,  that  we  rest  our  main  objec- 
tion to  its  credibility.  We  maintain,  that  they  have  taken  only  a 
one-sided  view  of  what  nature  presents  to  our  observation  ;  that  they 
have  paid  attention  to  those  facts  alone,  which  are  confirmatory  of 
phrenology,  and  shut  their  eyes  to  tliose  which  oppose  it.  In  order 
to  establish  what  they  consider  as  the  rule,  they  have  collected  to- 
gether all  the  instances  in  its -favour,  and  have  passed  over  or  sup- 
pressed all  the  exceptions.  What  we  assert  is,  that  more  enlarged 
inquiry,  conducted  with  a  more  entire  devotion  to  the  cause  of  truth, 
and  a  scrupulous  rejection  of  error,  would  have  shown  the  latter  to  be 
at  least  equal,  if  not  superior  in  number  to  the  former.  Our  own^  ob- 
servations, as  far  as  we  have  pursued  them,  have  led  us  to  this  conclu- 
sion ;  and  it  was  on  the  result  of  these  observations  that  our  scepticism 
was  principally  founded.  So  frequent,  indeed,  are  the  exceptions,  that 
even  the  founders  of  the  system,  Drs.  Gall  and  Spurzheim  themselves, 
on  applying  it  practically,  cominitted,  as  is  well  known,  very  glaring 
mistakes  ;  giving  frequently  the  most  false  judgments  of  the  characters 
of  various  individuals.  Have  these  mistakes,  we  may  ask,  been  any 
where  recorded  by  the  phrenologists,  and  candidly  set  off"  against  the 
instances  in  confirmation  of  their  sagacity  ?  What  avails  their  collec- 
tions of  thousands  of  examples  of  coincidences,  when  the  perhaps 
equally  numerous  instances  of  discordance  are  excluded  from  the  cata- 

*  Treatise  on  Insanity,  p.  465  to  474. 


496  APPENDIX. PHRENOLOGY. 

logue  ?  The  fact,  that  the  brain  of  Cuvier  was  of  unusual  magnitude, 
has  been  triumphantly  proclaimed  in  all  the  publications  on  phreno- 
logy ;  but  we  are  not  aware  that  any  phrenologist  has  brought  forward 
the  equally  well-certified  fact,  that  the  brain  of  Sir  Walter  Scott  was 
found  on  exan;iination  to  be  "  not  large."* 

In  like  manner,  a  long  catalogue  of  persons  avowing  their  belief  in 
phrenology,  including  many  men  of  eminent  talents  and  extensive 
knowledo-e,  has  been  paraded  before  the  public ;  but  we  have  not  yet 
seen  any  counter  list  of  unbelievers  prepared  with  the  view  of  ascer- 
taining, in  a  science  professedly  of  pure  observation,  on  which  side' 
the  weight  of  authorities  preponderates.  The  class  of  men  who,  from 
the  nature  of  theii*  pursuits,  are  perhaps  best  qualified  to  form  a  correct 
judgment  in  matters  of  this  nature,  are  the  members  of  the  medical 
profession  ;  yet  how  inconsiderable,  compared  with  the  total  number, 
is  the  proportion  of  those  belonging  to  that  profession  who,  according 
to  Mr.  Combe's  catalogue,  have  given  in  their  adhesion.  Sculptors, 
again,  compose  another  class  of  men  whose  studies  lead  them  more 
especially  to  the  most  minute  and  accurate  knowledge  of  the  external 
form  of  the  human  head ;  yet  amongst  the  many  who  are  at  present 
engaged  in  the  active  exercise  of  their  noble  art,  Mr.  Combe  has  been 
able  to  bring  forward  the  name  of  one  solitary  individual  as  lending  a 
countenance  to  phrenology. 

"  It  is  not  enough,"  as  Dr.  Prichard  very  justly  observes,  "to  have 
a  few  chosen  coincidences  brought  forward  by  zealous  partizans,  who 
go  about  in  search  of  facts  to  support  their  doctrine,  and  pass  by,  or 
really  cannot  perceive,  the  evidence  that  ought  to  be  placed  in  the  oppo- 
site scale.  The  principles  of  the  system  ought  to  be  applicable  in 
every  instance.  The  phrenologists,  however,  aware  of  numerous  and 
striking  exceptions,  elude  their  evidence  by  asserting,  that  when  ^ 
certain  portion  of  the  cranium  and  of  the  brain  is  greatly  developed, 
while  the  faculty  there  lodged  has  never  been  remarkably  distinguished, 
it  nevertheless  existed  naturally,  though  the  innate  talent,  for  want  of 
proper  cultivation,  has  never  been  displayed;  the  predominant  organic 
power  was  never  discovered  by  the  owner,  though  according  to  the 
principles  of  the  doctrine,  with  this  organic  power  a  proportional 
impulse  to  exertion,  or  an  instinctive  energy  is  combined,  which  com- 
municates of  itself  a  strong  and  irresistible  tendency  to  particular  pur- 
suits. When,  again,  a  strongly  marked  propensity,  or  a  decided  talent 
has  been  manifested  without  any  corresponding  amplitude  of  structure, 
it  is  in  like  manner  pleaded,  that  by  sedulous  exercise  and  culture,  a 
natural  deficiency  has  been  overcome.  Thus  the  phrenologist  avails 
himself  of  a  double  method  of  elusion  ;  his  position,  like  the  cave  of 
Philoctetes,  affords  him  an  escape  on  either  side ;  and  in  one  direction 
or  another  he  contrives  to  baffle  all  the  address  of  his  opponents. 

"  If,  however,  the  testimony  of  facts  in  a  great  scale  should  be 
found  adverse  to  the  alleged  coincidences,  or  to  the  correspondence 
of  given  mental  equalities  with  certain  conditions  of  the  brain,  phre- 
nology will  not  continue  to  make  proselytes,  and  ,it  will  be  ultimately 

•  Life  of  Sir  Walter  Scott,  by  Lockhart,  vol,  vii.  p.  395,  note. 


TESTIMONY   EVAJ)ED    BY    PHRENOLOGISTS.  497 

discarded   as   an   hypothesis   without   foundation.     At   present,  most 
inquisitive  persons  seems  to  b^  in  doubt  on  this  subject,  and  to  be 
looidng  out  for  evidence.     1  have   taken   every  opportunity  that  has 
occurred  to   me   for   many  years   of  making  inquiries  of  persons  who 
had  a  great  field  of  observation  within   their  reach,  what  had  been  the 
result  of  their  experience  on  this   subject.     Many  of  the  persons  have 
been    physicians,    who    were     superintendants    of    extensive    lunatic 
establishments.     Some    of  them    had    been   men    who    had   addicted 
themselves  to  the  study  of  phrenology,  and  were  predisposed  to  imbibe 
the  opinions  of  its  authors  :    some  have  been  persons  distinguished  by 
their   researches    in  the   anatomy  and    physiology  of  the    brain   and 
nervous  system.     Among  these  I  do  not  remember  to  have  found  one 
who   could   say  that  his   own   observation  had  aflorded  any  evidence 
favourable  to  the  doctrine.     Yet  we  should  imagine,  that  a  man  who 
lives  amongst  hundieds  of  monomaniacs  must  have  constantly  before 
his  eyes  facts  so  obvious  that  he  could  not  be  mistaken  in  their  bear- 
ing.    Some  hundreds,  and  even  thousands  of  such  persons  have  passed 
a  part  of  their  lives  under  the  inspection  of  M.  Esquirol,  who  possesses 
most  extensive  resources  for  elucidating   almost   every   subject  con- 
nected   with    the   history   of  mental   diseases,  and   has   neglected   no 
i'nquiry  which  could  further  the  attainment  of  that  object.     The  result 
of  his  observations  will  be  allowed  to  be  of  some  weight  on  the  decision 
of  this  question,  in  which  the  appeal  is  principally  to  facts  of  the  precise 
description  of  those  with  which  he  has  been  chiefly  conversant.     At 
his  establishment  at  Ivry  he  has  a  large  assemblage  of  crania  and  casts 
from  the  heads  of  lunatics,  collected  by  him  during  the  long  course  of 
his  attendance  at  the  Salpetriere,  and  at  the  Royal  Hospital  at  Charenton, 
which  is  under  his  superintendance.     While  inspecting  this  collection, 
I  was  assured  by  M.  Esquirol,  that  the  testimony  of  his  experience  is 
entirely  adverse  to  the  doctrine  of  the  phrenologists  ;  it  has  convinced 
him  that  there  is  no   foundation  whatever  in   facts  for   the   system  of 
correspondences  which  they  lay  down  between  given  measurements  of 
the  head  and  the  existence  of  particular  mental  endowments.     This 
observation  of  M.  Esquirol  was  made  in  the  presence  of  M.  Mitivie, 
physician  to  the  Salpetriere,  and  received  his  assent  and  confirmation. 
M.  Foville,  physician  to  the  extensive  lunatic  asylum  at  St.  Yon,  gave 
me  a  similar  assurance.     There  are  few  individuals  in  Europe  whose 
sphere  of  observation  has  been  so  extensive  as  that  of  M.  Esquirol  and 
M.  Foville,  and  certainly  there  are  none  wliose  science  and   habits  of 
observation  better  qualify  them   to  be  witnesses  in  such  a  subject  of 
inquiry;  but  testimonies   to  the  same  result  may  be  collected  from 
unbiassed  witnesses,  whose  evidence  taken  collectively  may  have  nearly 
equal  weight.     Among  these  there  are  men  unscientitic,  though  capable 
of  correct  and   unprejudiced   observation,   as  well   as   anatomists   and 
physiologists.     In  the  number  of  the  latter  is  Rudolphi,  who  declares 
that  he  has  examined   many  hunderds   of  brains  without  finding  any 
thing  that  appeared  to  him  favourable  to  the  phrenological  theory."* 

*  Treatise  on  Insanity,  pp.  476,  477, 
«    43* 


498  APPENDIX. PHRENOLOGY. 

The  mode  in  which  Dr.  Combe. evades  the  force  of  the  strong  testi- 
mony here  adduced,  is  quite  characteri^stic  of  the  disposition  to  be  found 
amongst  confirmed  phrenologists,  of  resolutely  rejecting  all  evidence 
that  militates  against  the  system  they  have  adopted.     Thus,  he  says, 
in   reference  to  the   passage  vi^e   have  just  quoted,  "If  Dr.  Prichard 
believes  that  the  intelligent  and   benevolent  Esquirol,  is   that  person," 
(namely,  one  "  competent  to  form  a  judgment  on  the  subject,")  and  if 
his  collection  of  crania  and  casts  be  the  hostile  evidence  vi^hich  is  relied 
on,  this  only  proves,  in  a  forcible  manner,  that  Dr.  Prichard  is  himself 
not  competent  to  judge,  or  that  he  has  not  taken  time  either  to  examine 
the  collection  of  crania,  or  to  ascertain  the  competency  of  Esquirol  and 
Metivie,  to  decide  on  the  merits  of  the  question  on  which  they  volun- 
teered an  opinion."*     We  cannot  help  remarking  here,  that,  on  another 
occasion,  when  criticising  the  suggestion  Ave   threw  out,  in  the  Essay 
on   Cranioscopy,  of  the    propriety  of  inquiring   into   the  talents  and 
qualifications  of  observers  before  admitting  the  truth  of  the  facts  received 
on  their  testimony,  a  very  different  language  was  held.     "  When  they" 
(the  advocates  of  phrenology)  "affirm  that  the  subjects  of  observation 
are  patent  to  the  whole  world,  who  have  eyes  to  see,  and  understandings 
to  comprehend ;    and   when   they  say,   compare   manifestations   with 
cerebral  development,  and  you  are  at  the  bottom  of  the  problem  yourself; 
what  need  for  inquiry  into  their  talents  and  qualifications  to  observe?" 
"  When    Gay   Lussac   hears   that   Sir    Humphry   Davy   has   made   a 
discovery  in  chemistry,  and  reads  Sir  Humphry's  statement  of  the  way 
in  which  it  was  made,  does  he  begin  by  inquiring  first,  whether  it  be 
possible  to  make  the  discovery  at  all,  seeing  natural  substances  are  'so 
changed  and  modified,  exalted  and  subdued'  by  a  multitude  of  powerful 
causes  ?     And,  after  settling  this   point,  does   he,  in  the  secoml  place, 
proceed  to  inquire  into  Sir  Humphry  Davy's  talents  and  qualifications 
as  a  chemist,  and  into  his  capacity  to  make  the   discovery,  and  then 
believe  it,  or  not,  according  to   the  result  of  this  investigation  ?     No 
man  who  knows  the   first  rudiments  of  philosophy  would   follow  so 
absurd   and   preposterous   a  course.     What  should  we   think   of  Gay 
Lussac's  refutation  of  Sir  Humphry's  discovery,  founded  on  a  meta- 
physical inquiry  into  the  possibility  of  making  it,  and  into  the  '  talents 
and  qualifications'    of  the  discoverer  ?     We  should  pity  him  for  his 
ignorance  of  the  rudiments  of  philosophy. "f 

This  happy  talent,  possessed  by  the  champions  of  phrenology,  of 
shaping  their  course  either  one  way  or  the  opposite,  according  as  it 
may  suit  the  convenience  of  the  occasion,  enables  them,  at  one  time, 
to  proclaim,  that  the  evidences  of  their  science  are  palpably  and  de- 
monstrative, that  the  field  of  nature  is  open  to  all  inquirers,  that 
"  every  one  who  has  eyes  may  see"  and  judge  for  himself;  and  at 
another,  when  such  judgment  is  against  them,  they  can  turn  round, 
and  allege  that  in  order  to  arrive  at  the  truth  a  peculiar  discretion  and 
tact,  acquired  by  long  experience  and  careful  appreciation  of  minute 

*  Phrenological  Journal,  viii.  p.  654. 
-j- Essays  on  Phrenology,  p.  71.     ' 


PROCESS   OF    VEKIFICATION.  499 

and  hair-breadth  differences  of  size  is  necessary.  They  can  then 
declare  that  the  observer  who  has  not  arrived  at  the  same  conchisions 
as  themselves,  is  doubtless  incompetent  to  the  task  he  has  attempted  ; 
and  that  his  testimony,  being  of  no  value,  ought  to  be  wholly  set 
aside. 

Let  it  be  borne  in  mind,  then,  by  the  practical  inquirer  into  the  truth 
of  phrenology,  that  he  will  not   be   esteemed   qualified  to  verify  its 
doctrines,  unless  he  be  previously  deeply  versed  in  the  new  system 
of  psychology,   can    assign    to    each   of  the   thirty-five    special    and 
primary  faculties  of  the  soul  its  sphere  of  operation,  and  has  acquired 
a  readiness  in  unravelling  their   multifarious   combinations,  so  as  to 
analyze,  by  this  subtile  metaphysical  chemistry,  all  human  qualities 
into  their  proximate  and  ultimate  elements,  refer  all   actions   to  their 
proper  innate  impulses,   and  assign   the   proportions  of  the  various 
ingredients  which  are  mixed  up  in   the  formation  of  the   character  of 
each  individual.     No  one  is  competent  to  excel  in  this  new  branch  of 
philosophy  who  doubts  the  possibility  of  appreciating  the  intensities  of 
moral  or  intellectual  qualities  by  geometrical  measurements,  on  scales 
divided  into  tenths  and  hundredths  of  inches.     The  young  and  ardent 
phrenologist,  who  after  having  applied  his  callipers  to  the  skull  sub- 
jected to  his  examination,  and  taken  a  note  of  the  dimensions  of  each 
of  the  thirty-five  organs,  proceeds  to  verify  his  observations  by  com- 
paring them  with  the  character  of  the  possessor  of  those   organs,  will 
never  fail  to  meet  with  ivonderful  coincidences,  sufficient  to  give  him 
the  greatest  satisfaction,  and  confirm  him  in  the  persuasion  that  he  pos- 
sesses the  real  key  to  the  secrets  of  nature   in   the  hitherto  recondite 
science  of  mental  philosophy.     A  moderate  share  of  dexterity  in   re- 
conciling apparent  discrepancies  will  suffice  to  ensure  a  preponderance 
of  favourable  evidence  ;  since,  fortunately,  there  have  been  provided  in 
the  brain  different  organs,  sometimes  of  similar  and  sometimes  of  opposite 
properties,  capable,  by  a  litde  adjustment  o{  plus  or  minus  on  either 
side  of  the  equation,  of  furnishing  the  requisite  degrees  of  the  mental 
quality  sought  for,  and  of  thus  solving  every  psychological  problem. 
We  shall  suppose,   for  instance,   that  he  is  inspecting  the  head  of  a 
person  known   to  have  given  credit  to  the  prophecies  of  a  weather 
almanac  ;  he  finds,  on  reference  to  the  "  system  of  phrenology,"  that 
a  belief  in  astrology  is  the   oflTspring  of  No.  16,  that  is,  ideality  ;  so 
that  if  this  organ  happen  to  be  sufficiently  large,  the  phenomenon  is  at 
once  accounted  for.     But  if  it  be  not,  our  phrenologist  will  have  an- 
other chance  ;  for  he  will  probably  discover  it  to  arise  from  the  dimen- 
sions of  No.  15,  which  inspires  hope,  the  source  of  \he  propensity  to 
credulity.     Habitual  irresolution  may  result  either  from  the  magnitude 
of  No.  12,  or  thediminutiveness  of  18  ;  thus  affording  very  great  con- 
venience for  making  our  observations  of  the  character  square  with  those 
of  the  dimensions  of  the  organs,  and  vice  versa.     If,  again,  the  magni- 
tude of  the  organ  of  combativeness  accord  with  the  manifestations  of 
pugnacity  given  by  the  individual,  it  is  well,  and  we  need  inquire  no 
farther,  but  set  it  down  at  once  as  an  irrefragable  proof  of  the  accuracy 
of  phrenological  determinations.     Should   the  correspondence,  how- 


500  APPENDIX. PHRENOLOGY. 

ever,  not  prove  satisfactory,  the  organ  being  large  for  instance,  and  the 
manifestation  small,  we  have  then  further  to  examine  the  dimensions 
of  the  organ  of  caution,  the  influence  of  which  is  to  moderate  and 
check  the  operation  of  the  fornier  ;  and  we  shall  perhaps  find  this 
organ  sufficiently  large  to  account  for  the  phenomenon.  -Both  these 
organs  may  be  large,  or  both  small,  or  the  first  may  be  small  and  the 
second  large,  or  the  converse  ;  and  other  modifications  of  action  may 
result  if  either  one  or  both  be  only  of  moderate  size,  allowing  great 
latitude  of  choice  in  the  a.ssignment  of  motives.  Should  we  be  so 
unfortunate  as  to  exhaust  all  the  combinations  without  meeting  with 
the  success  we  desire,  there  is  still  an  abundance  of  auxiliary  faculties 
of  which  we  may  avail  ourselves  with  advantage.  If  we  were  to  ex- 
plain the  fact  of  the  individual  in  question  having  accepted  a  challenge, 
he  might  have  been  inspired  by  combativeness,  whose  voice  was 
"  still  for  war,"  or  goaded  on  by  destrudiveness,  to  fight  that  he 
might  destroy ;  firmness  may  have  urged  him  to  persevere  by  the  con- 
sideration that  he  had  previously  resolved  it,  and  concenirativeness,  by 
rivetling  his  attention  to  the  subject,  may  have  screwed  his  courage  to 
the  sticking  place ,  or  he  may  have  been  prompted  by  imitation  to 
follow  the  example,  or  by  approbation  to  gain  the  applause  of  his 
friends.  We  have  also  to  take  into  the  account  the  countervailing 
influence  of  faculties  which  are  pulling  in  the  opposite  direction,  and 
qualifying  the  combined  powers  of  the  former  incentives:  And  should 
cautiousness  not  be  in  sufficient  force,  we  are  to  consider  the  power  of 
conscientiousness,  which  preaches  forbearance,  meekness,  and  forgive- 
ness ;  of  veneration  which  appeals  to  the  high  authority  of  religion 
and  of  law  ;  of  benevolence  restraining  the  hand  from  inflicting  pain 
and  death  ;  of  approbation,  who  qualifies  her  sanction  by  raising  other 
voices  condemnatory  of  the  deed  ;  and  last,  though  not  least,  the  love 
of  life  which  recoils  with  instinctive  dread  from  the  possible  catas- 
trophe. Drawing,  then,  a  diagrjim  of  all  these  component  moral 
forces,  in  their  proper  directions,  and  suitable  proportions,  it  will  not 
be  very  difficult  to  obtain  by  this  artificial  dynamieo-phvenological 
process,  the  exact  resultant  which  corresponds  with  the  actual  fact  to 
be  explained. 

Lest  it  should  be  imagined  that  the  above  description  is  a  caricature 
of  the  new  method  of  philosophizing,  so  admirably  calculated  to  esta- 
blish the  truths  of  phrenology,  we  shall  beg  to  quote  the  following 
passage  from  Sir  George  Mackenzie's  Illustrations,  as  an  example  of 
this  satisfactory  process  of  ratiocination. 

"  In  discussing  the  conjectured  faculty  of  inhabitiveness  with  Mr. 
Combe,  he  had  the  goodness  to  make  us  acquainted  with  a  case,  in  which 
locality  and  inhabitiveness  were  both  very  moderate  in  development, 
but  the  propensity  to  wander,  as  he  informed  us,  very  powerful.  Dr. 
Spurzheim  mentions  this  propensity  as  belonging  to  locality,  and  he 
states  several  remarkable  cases  in  which  the  organ  was  much  deve- 
loped, and  the  propensity  strong.  The  case  referred  to  by  Mr.  Combe 
was,  on  this  account,  interesting ;  and  we  will  state  the  result  of  our 
inquiries  into  the  particulars,  for  the  purpose  of  giving  an  example  of 


INFLUE^CE    OF    EDUCATION".  501 

the  caution  with  which  we  ought  to  receive  the  description  of  any  case 
brought  in  opposition,  since  it  sometimes  appears  to  be  necessary  even 
among  friends. 

"  The  young  man  to  whose  case  we  refer,  had  a  very  strong  desire 
to  adopt  a  seafaring  life,  contrary  to  the  wishes  of  his  friends.  It  oc- 
curred to  them,  that  a  voyage  up  the  Baltic,  during  the  stormy  months 
of  October  and  November,  might  have  the  effect  of  giving  him  a  dis- 
gust to  the  profession  for  which  he  showed  so  ardent  a  desire.  He 
suffered  so  many  privations  and  hardships,  that  he  yielded  to  the 
wishes  of  his  friends,  although  the  desire  to  go  to  sea  continued  as 
strong  as  ever.  On  proposing  a  few  questions,  we  found  that  the  pro- 
pensity was  confined  to  being  at  sea;  that  this  propensity  did  not 
originate  in  a  desire  to  wander ;  for  neither  travelling  on  land,  nor 
mere  change  of  place,  would  have  gratified  the  propensity.  At  the 
same  time,  the  person  referred  to  declared,  that  regular  voyages  to  the 
same  place  would  not  have  satisfied  him.  The  propensity  had  haunted 
him  as  long  as  he  could  remember  any  thing.  Being  anxious  himself 
to  contribute  to  the  unravelling  of  what  appeared  mysterious  and  irre- 
concilable to  the  system,  he  stated  that  he  used  to  go  once  or  twice 
a-day  to  examine  the  mechanism  and  rigging  of  ships  in  Leith  har- 
bour, an  employment  of  which  he  was  passionately  fond ;  and  long 
before  he  commenced  his  trial  voyage,  he  had  become  familiar  with 
the  names  and  uses  of  every  part  of  a  ship,  and  of  the  rigging.  He  was 
fond  of  machinery,  and  has  often  amused  himself  by  making  models  of 
ships ;  and  his  mechanical  turn  was  so  strong,  that  he  had  constructed 
a  model  of  machinery,  by  which  a  ship's  motion  may  be  applied  to 
work  the  pumps.  This  mechanical  propensity,  and  his  early  attach- 
ment to  naval  machines,  together  with  firmness,  appear  to  us  to  have 
given  rise  to  his  desire  for  a  sea-faring  life.  Courage  might  also  have 
prompted  his  wish  to  enter  the  navy.  Thus  the  supposed  propensity 
to  wander  appeared  not  to  exist ;  and  it  was  found  that  a  mechanical 
genius,  an  early  attachment*  to  the  mechanism  of  a  ship,  perseverance, 
courage,  and  probably  also  love  of  approbation,  or  ambition,  and 
ideality,  all  of  which  were  well  developed  in  the  individual  referred  to, 
combined  to  inspire  the  desire  to  enter  the  navy."  (Illustratioris  of 
Phrenology,  p.  170.) 

It  is  to  be  lamented  that,  at  the  period  when  this  elaborate  investi- 
gation was  undertaken,  the  organ  of  wonder  had  not  yet  been  made  ; 
for  as  one  of  the  functions  of  this  organ,  according  to  Mr.  Combe,  is  to 
"  incite  young  men  to  choose  the  sea  as  a  profession,"  much  light 
would  have  been  thrown  upon  the  object  of  the  inquiry  by  a  critical 
examination  of  its  dimensions  compared  with  those  of  all  the  other 
organs  which  were  taken  info  consideration  as  combining  their  influ- 
ence in  producing  the  result. 

There  is  this  very  remarkable  peculiarity  in  the  pursuit  of  phre- 
nology, that  the  student  is  perplexed,  not  with  the  difficulties,  but 

*  "  Dr.  Spurzheim  has  shown,  that  the  faculty  of  attachment  extends  its  influ- 
ence to  inanimate  things,  as  well  as  to  animate  beings." 


502  APPENDIX. PHRENOLOGY. 

with  the  facilities  it  affords  for  explaining  every  phenomenon.  The 
pliability  of  its  doctrines  is  exemplified,  not  merely  in  the  analysis  of 
motives,  but  likewise  in  the  influence  vi^hich  we  are  allowed  to  ascribe 
to  the  habitual  exercise,  or  education  of  the  faculties.  The  observed 
magnitudes  of  the  respective  organs  indicate,  not  the  acquired,  but  the 
natural  powers,  sentiments,  and  propensities.  Now,  the  character  of 
the  individual  is  the  joint  result  of  the  force  of  natural  endowments, 
and  of  the  amount  of  moral  and  intellectual  cultivation  which  has  been 
bestowed  upon  them.  But  can  we  ever  know  enough  of  the  minute 
history  of  the  progress  of  the  mind  of  any  individual  to  enable  us  to 
form  a  correct  estimate  of  the  relative  power  of  these  two  elements, 
which  have,  in  the  formation  of  each  respective  faculty,  combined 
their  operations  ?  If  it  be  true  that  an  organ  may  be  the  seat  of  a  faculty 
varying  in  its  activity  according  to  the  occasions  which  call  it  forth, 
by  what  physical  criterion  can  we  distinguish  the  active  from  the 
dormant  conditions  of  that  organ  ?  Unless  we  can  draw,  with  pre- 
cision, these  distinctions,  it  is  evident  that  the  ground  of  all  craniosco- 
pical  observation  is  cut  from  under  us. 

It  may  be  indeed  alleged,  that  at  all  periods  of  life,  and  even  after 
the  bones  of  the  skull  are  consolidated,  the  organs  increase  or  diminish 
in  size  according  to  the  exercise  or  disuse  of  the  faculty  associated 
with  it,  whether  such  change  may  have  been  brought  about  by  voluntary 
training,  or  by  the  discipline  of  circumstances  ;  and  certainly,  if  such 
were  the  fact,  our  experience  would  repose  on  a  much  surer  basis, 
than  if  the  form  of  the  organs  merely  retained  the  stamp  originally 
impressed  upon  them  by  nature.  But  the  hypothesis  that  the  cerebral 
organs  acquire  additional  size  by  the  exercise  of  their  powers  was  posi- 
tively rejected  as  untenable  by  Dr.  Spurzheim,  as  we  have  heard  him 
publicly  declare  ;  and  it  is,  we  believe,  repudiated  by  the  generality  of 
phrenologists. 

We  do  not  think  it  difficult  to  account  for  the  progress  which  phre- 
nology has  made  amongst  the  very  numerous  class  of  persons  who 
find  in  it  a  source  of  agreeable  occupation,  giving  exercise  to  their  inge- 
nuity in  discovering  striking  coincidences,  and  gratifying  their  self- 
complacency  by  inspiring  them  with  the  fancy  that  they  are  penetra- 
ting far  into  the  mystic  regions  of  psychology.  For  the  last  twenty 
or  thirty  years,  various  popular  writers,  and  lecturers  without  number, 
have  been  displaying  their  powers  of  elocution,  exercising  their  skill 
in  the  critical  examination  of  developments,  and  expounding  the  doc- 
trines of  the  new  philosophy  to  wondering  and  admiring  audiences. 
With  all  these  advantages  and  appliances  to  boot,  the  wonder  seems 
to  be  not  that  phrenology  has  met  with  the  success  of  which  so  much 
boast  is  made,  but  that  it  has  not  speedily  gained  the  universal  assent ; 
for  had  it  been  a  real  science,  like  that  of  Chemistry  and  other  branches 
of  Natural  Philosophy,  founded  on  uniform  and  unquestionable  evidence, 
it  could  not  have  failed,  by  this  time,  of  being  generally  recognised  as 
true. 

When  we  consider  that  the  present  age  is  not  one  in  which  there  is 
any  lack  of  credulity,  or  in  which  a  doctrine  is  likely  to  be  repudiated 


PROGRESS   OF    PHRENOLOGY.  503 

on  the  score  of  its  novelty  or  its  extravagance,  we  cannot  but  smile  at  the 
complaints  of  persecution  uttered  by  the  votaries  of  the  system  of  Dr. 
Gall,  and  at  the  attempts  they  make  to  set  up  a  parallel  between  its 
reception  in  this  country,  in  these  times,  and  that  which,  two  centuries 
ago,  attended  the  speculations  of  Galileo,  and  subjected  him  to  the 
tyrannous  cognisance  of  the  Inquisition ;  or  to  establish  an  analogy 
between  the  dogmas  of  phrenology  and  the  discoveries  of  the  circula- 
tion of  the  blood,  and  of  the  analysis  of  light,  which  have  immortalized 
the  names  of  Harvey  and  of  Newton. 


INDEX. 


THE  NUMBERS  REFER  TO  THE  PARAGRAPHS. 


Those  references  to  which  the  word  (note)  is  attached  have  been  added  in  the   American 

edition. 


Abeildgaard,  436. 
Aberration,  chromatic,  670. 

parallactic,  667. 

of  retrangibility,  670  (note). 

spherical,  665. 

Absorbent  system,  539. 
Absorption,  interstitial,  551. 

lacteal,  38,  40,  538. 

lymphatic,  45. 

venous,  45  (note). 

Abstinence,  effects  of,  324. 
Acalepha,  1114. 
Acephala,  1085. 
Acid,  lactic,  519. 

in  stomach,  347. 

Acini,  499,  505. 

Acoustics,  623,  757. 

Actinia,  1115. 

Adelon,  84  (and  note),  50  (note). 

Adipose  texture,  122. 

Admyrauld,  615. 

iEthmoid  bone,  617,  940. 

Agastrica,  1120. 

Age,  570,  858. 

Air  bladder,  1061. 

Alar  ligaments,  170. 

Albinus,  113,  178. 

Albugineous  ^bre,  114,  165. 

Albumen,  285,  517. 

Albuminous  secretions,  514. 

Alison,  86. 

AUantois,  848, 1020. 

American  race,  875. 

Ammonia,  formation  of,  270. 

Amnios,  844,  851. 

Amphiuma,  1044. 

Amphibia,  949. 

Ampulla,  632. 

Anaesthesia,  709. 

Analysis,  ultimate,  272. 

Anastomoses,  423. 

Anatomy,  .56. 

Animal  kingdoin,  2. 


Animal  food,  313.  , 

Animalcules,  spermatic,  810. 
Annelida,  1092. 
Annulus  ovalis,  412. 
Antagonist  powers,  570. 
AntennsB,  1094,  1104. 
Antiquity  of  man,  72.        ( 
Antiseptic  power,  342. 
Antitragus,  627. 
Antra  inguinalia,  962. 
Aponeuroses,  156,  161. 
Apparatus  neurothelic,  178  (note). 

blennogenous,  183  (note). 

chromatogenous,  179  (note). 

diapnogenous,  555  (note). 

Appendices  pyloricse,  1054. 
Applications  of  Physiology,  57. 
Aqueous  secretions,  512,  513. 

exhalations,  484. 

humor  of  the  eye,  649. 

Arabians,  1139. 
Arachnoid,  133. 
Arachnida,  1096. 
Archseus,  7,  101. 
Area  vasculosa,  1020. 
Areola,  828. 
Areola  pellucida,  1020. 
Aristotle,  1131. 
Arrangement  of  functions,  77. 

ancient,  81. 

Adelon,  Beclard,  &c.  84. 

Bichat,  83. 

Bostock,  85. 

Cuvier,  84. 

Dumas,  83. 

Dunglison,  84  (note). 

Haller,  82. 

Magendie,  84  (note). 

/Mayo,  87. 

Richerand,  82. 

Roget,  88. 

D  Azyr,  82. 

Arteries,  42. 


43 


506 


INDEX. 


Arterise  helicinae,  809. 
Arterial  system,  418. 
Arterial  action,  458. 
Articulate  sounds,  768. 
Articulata,  68,  1U90. 
Articulations,  167,  244. 
Aryteenoid,  759. 
Ascidia,  1089. 
AsELLi,  377,  1150. 
Asterias,  1108. 
Assimilation,  39,  307. 
Association,  702,  704. 
Attraction,  107. 

of  life,  223. 

Automatic  motions,  728. 
Auricle,  412. 

AVICENNA,  1139. 

Babington,  Dr.  B.  407  (and  note). 
Baer,  803,  804. 
Baillie,  582. 
Balance  of  afRnities,  265. 
Barry,  Dr.  M.  799,  800. 
Bartholin,  1151. 
Base  of  support,  250. 
Bat,  937. 
Batrachia,  1041. 
Bauer,  199,  395,  401,  585. 
Bear,  942. 

Beaumont,  323  (note),  347  (note), 
349  (note). 

Beaver,  957. 

Beclard,  84,  117,  199,  585. 
Bee,  1102. 

Bell,  Sir  Charles,  615  (note),  720, 
724,  731,  769. 

Bennati,  772. 

Benson,  143. 

Berres,  588  (note). 

Berzehus,  passim. 

Bichat,  passim. 

Bile,  40,  864. 

Biology,  1. 

Birds,  1003.  / 

Bivalves,  1085. 

Blainville,  73. 

Blane,  208. 

Blastoderma,  831. 

Blennogenous  apparatus,  183  (note). 

Blood,  42,  383. 

Blumenbach,  passim. 

Blundell,  447  (note). 

Boerhaave,  113,  392,  504,  1156. 

BoissiER,  558  (note). 

Bones,  30,  35,  137,  565. 

Bonnet,  69. 

BoRELLi,  198,  436, 1008.J 


BosTocK,  passim. 
Botany,  2. 
Botts,  983. 

BOUDET,  407. 

Bourdon,  84. 

BoGER,  511  (note). 

Brain,  14,  173,  521,  581,  749,  1014. 

Branchiffi,  1045,  1060. 

Brande,  287,  303,  386,  399,  404. 

Breschet,  178,  (note),  179  (note), 

183,  (note),  555  (note). 
Broughton,  615  (note). 
Brevipennes,  1021. 
Brown,  100. 
BuFFON,  154  (note),  818. 
Bulbus  arteriosus,  1059. 
Bulbus  glandulosus,  1009- 
Bulla  ossea,  829. 
Bullffi  turbinatae,  1017. 
BuRDACH,  588  (note). 
Bursa  faucium,  992. 
Bursa  Fabricii,  1010. 
Bursse  mucosae,  170. 
Butt,  403. 
Butter,  522. 
Byssus,  1087. 


Cadet,  368  (note),  , 

CjESAlpinus,  1148. 

Callus,  567. 

Camel,  992. 

Camel opard,  993. 

Campanula,  1065. 

Camper,  904.  \ 

Canals,  131. 

Canalis  Petitianus,  650. 

Cancelli,  139. 

Canon  bone,  879. 

Capillaries,  428,  429, 464. 

Capsules,  1-56,  1.59. 

Capsule  of  the  lens,  650. 

joints,  170. 

vitreous  humor,  648. 

Capsular  ligament,  171. 
Caput  Gallinaginis,  807. 
Carbon,  49,  271. 
Carbonic  acid,  481. 
Carlisle,  198,  936. 
Carnese  columnss,  410. 
Carpenter,  103,  note. 
Cartilages,  147. 

Cartilages,  articular,  or  diarthrodial-. 
151, 169. 

interarticular,  1-52. 

interosseal,  150. 

raembraniform,  14t7. 


INDEX. 


507 


Cartilages,  temporary,  148. 

semilunar,  171. 

of  larynx,  761. 

Caruncula  lacrymalis,  654. 

Carunculae  myrtiformes,  818. 

Cassowary,  1021. 

Carus,  432  (note). 

Carus,  1097. 

Cat,  948. 

Caterpillar,  110.3. 

Catoptric  examination  of  the  eye,  657 

(note). 
Caucausian  race,  872. 
Cavallo,  393. 
Cellular  texture,  32,  118. 
Centre  of  gravity,  252. 
Cephalopoda,  1079. 
Cerebellum,  582,  925. 
Cerebral  substance,  520. 
Cerebrum,  582. 
Ceruminous  glands,  628. 
Cetacea,  996. 
Chalazee,  821,  1019. 
Chameleon,  1033. 
Chaussier,  114,  165,  179, 181. 
Cheeks,  607. 
Cheek  pouches,  960. 
Cheese,  519. 
Chiroptera,  937. 
Chelonia,  1027. 
Chemical  functions,  38,  307. 
Chemical  conditions  of  organized 

matter,  263. 
Cheselden,  178. 
Chevalier,  183. 
Chevreul,  407. 
Choleric  temperament,  865. 
Cholesterine,  518. 
Chondropterygii,  1046. 
Chordae  tendineae,  410. 
Chorda  tympani,  631. 
Chordae  vocales,  761. 
Choroid  coat,  645. 
Chorion  of  teeth,  568. 
Chorion,  792,  830. 
Christison,  386  (note). 
Chromatic  aberration,  670. 
Chromatogenous  apparatus,  179  (note). 
Chossat,  558  (note). 
Chyle,  40,  356. 
Chylification,  40,  354. 
Chyme,  39. 
Chymificatioii,  338. 
Cicatricula,  823,  1020. 
Cilia,  653. 
Ciliary  circle,  647. 

ligament,  647,  669. 

processes,  647. 


Cineritious  substance,  582, 
Circle  of  Petit,  650. 
Circulation,  38,  42,  102,  408. 

proofs  of,  443. 

Classification,  zoological,  60,  64. 

of  tastes,  613. 

of  odours,  621. 

of  Cuvier,  67. 

Claviculi  of  bone,  143. 
Clitoris,  818. 
Cloaca,  848. 
Cloak,  1077. 
Coagulable  lymph,  391. 
Coagulation  of  albumen,  286. 

of  blood,  387. 

by  gastric  juice,  342. 

Coalescence  of  impressions,  682. 

Coats  of  blood-vessels,  415. 

Cochlea,  633. 

Coffin  bone,  979,  980. 

Colliquamentum,  831. 

Columna  nasi,  617. 

Colon,  40. 

Complementary  colours,  685. 

Complexity  of  organize  d  matter,  263. 

Conception,  820. 

Concha,  628. 

Concoction,  .350. 

Condiments,  320. 

Conglobate  glands,  495. 

Conglomerate  glands,  499. 

Coni  vasculosi,  798. 

Connexions,  mechanical,  167. 

Consonants,  771. 

Contractility,  93,  201. 

Constituents,  animal,  268. 

Continuous  gradation,  theory  of,  69. 

Convolutions,  582. 

Cow  PER,  198. 

Corion,  177. 

Cornea,  644. 

Coronet  bone,  979. 

Corpus  aurantianum,  411. 

cavernosum,  818. 

ciliare,  647. 

luteum,  820. 

papillare,  178. 

— —  spongiosum,  808, 
Corpusculum  Morgagni,  411. 
Corrugation,  cellular,  121,  226. 
Cortical  substance,  582. 
Cotulae,  506. 

COTUNNIUS,  634. 

Cotyledons,  833. 
Cowper's  glands,  800. 
Cranium,  229. 
Crassamentum,  385,  391. 
Crawford,  387,  489. 


508 


INDEX. 


Cribriform  plate  of  ear,  635. 
Cricoid,  762. 
Crocodile,  1032. 
Crop,  1009,  1081. 
Crucial  ligaments,  172. 
Cruickshank,  179,  181,  556,  558 

(note). 
Cruor,  385. 

Crura  corporis  spongiosi  urethras,  80i 
Crusta'petrosa,  970. 
Crustacea,  1094. 
Crypts,  188. 
Crystalline  lens,  648. 
CuLLBN,  101,  317,  1158. 
Cumulus,  803. 
Cupola,  633. 
Cuticle,  180. 
Cuttle-fish,  1079. 
CuviER,  67,  71,  73,  84,  &c. 
Cyanogen,  270. 
Cysticule,  1067. 

Dalton,  484. 

Davtos,  805. 

Darwin,  Charles,  861. 

Davy,  John,  142,  386  (and  note). 

Death,  37,  858. 

Decidua,  833. 

Decline,  570. 

Decussation  of  nerves,  718. 

Deer  genus,  68. 

Defoecation,  40. 

Deglutition,  39,  336. 

De  Graae,  797, 1154.  - 

De  la  Torre,  393,  585,  588. 

Deleau,  764. 

Delirium,  701. 

Dkmocritus,  1127. 

Dentition,  568. 

Derham,  75. 

Descartes,  691,  698. 

Design,  79. 

Development,  51. 

Deyeux,  387,  403. 

Diaphragm,  472. 

Diaprogenous  apparatus,  555  (note). 

Diastole,  441. 

Digestion,  39,  102,  338. 

Digitigrada,  944. 

Discus  proligerus,  799. 

Diploe,  139. 

DODART,  763. 

Dog,  946. 

Dorsal  vessel,  1097. 
DoLLiNGER,  432  (note). 
Draco  volans,  1034. 
Dreaming,  753. 
Drelincourt,  822. 


Duct,  131. 

Ductus  arteriosus,  851,  853. 

pneumaticus,  1061. 

venosus,  851,  853. 

vitello-intestinalis,  1020. 

Duhamel,  143,  560. 
Dumas,  199,  222,  336. 

DUMERIL,  66. 

Duncan,  386,  (note). 

DuNGLisoN,  84  (note),  323  (note),  347 

(note),  509  (note). 
Duodenum,  40,  364,  851. 
Dura  mater,  133,  158. 
Duration  of  impressions,  680. 

DUTROCHET,  199. 

Ear,  626,  1016. 

Ear-drum,  629. 

Eberle,  340  (note). 

Echinus,  1109. 

Echinodermata,  1107. 

Education^  856. 

Edwards,  116,  199,  585. 

Edwards,  Milne,  396. 

Egyptians,  1125. 

Ehrenberg,  588  (note),  785. 

Ejaculatores  seminis,  809. 

Elasticity,  120, 

Elasticity  of  arteries,  461. 

Electrical  fishes,  1069. 

Elemental  material,  112. 

Elements,  animal,  268,  275. 

Elephant,  968. 

Elongation,  210.     / 

Elliotson,  588  (note). 

Emmert,  588  (note). 

Emmet,  347  (note). 

Emboitement,  theory  of,  827. 

Emphysema,  119. 

Emotions,  732. 

Emunctories,  48. 

Endosmose,  548. 

Ent,  428. 

Entozoa,  1112. 

Epididymis,  805. 

Epidermis,  180. 

Epidermoid  substance,  114. 

Epigenesis,  828. 

Epiglottis,  760. 

Erasistratus,  1133. 

Erect  position,  894.  , 

Erectile  tissue,  434,  800,  801. 

Ethiopian  race,  874. 

Eustachian  tube,  630. 

Eustachian  valve,  412. 

EUSTACHIUS,  1145. 

Evolution,  50. 
theory  of,  827. 


INDEX. 


509 


Evolution,  fetal,  837. 
Excito-motory  system,  741. 
Excretion,  48,  553. 
Excretory  duct,  43,  506. 
Exhaustion,  209. 
Expiration,  477. 
Eye-ball,  641,  642. 
Eye-lids,  653. 

Fabricius,  1146. 

Face,  bones  of  the,  234. 

Facial  angle,  904,  905. 

Falciform  bones,  941. 

Fallopian  tubes,  821. 

Fallopius,  1145. 

Falsetto  voice,  770. 

Faraday,  681. 

Farina,  315. 

Fasciae,  34,  156. 

Fascicular  ligaments,  172. 

Fasciculi  of  muscular  fibres,  194. 

Fat,  47,  122,  5  J  9. 

Fecundation,  50,  789. 

Fermentation,  351,  533. 

Ferrien,  755. 

Fibrin,  294. 

Fibrinous  secretions,  517. 

Fibro-cartilaginous  textures,  153. 

Fibrous  tissues,  34,  155,  164. 

Fibrous  membranes,  158. 

Fibrous  capsules,  159. 

Figura  vasculosa,  1020. 

Filtration,  534. 

Fimbria,  816. 

Final  causes,  8,  78. 

Fingers,  258. 

Fishes,  1045. 

Fletcher,  669  (note). 

Fluids  and  solids,  proportion  of,  111. 

Focal  adjustment,  659. 

Fohman,  1057. 

Follicles,  188,  502,  5^33. 

FONTANA,  198,  588. 

Food,  311. 

,  animal,  313. 

,  vegetable,  314. 

Foot,  250,  1086. 
Foot  of  moUusca,  1086. 
Foramen  coecum  Morgagni,  611. 
Foramen  centrale  of  Sommerring, 

651. 
Foramen  ovale  et  rotundum,  85L 

FORDYCE,  317. 

Fossa  ovalis,  412. 
Fossil  remains,  71- 
FoujiCROY,  386,  398,  511,  &c. 
Fractured  bones, 
Fraenum  labiorum,  607. 


43^ 


Fraenum  linguae,  611. 

Frog,  1041. 

Fuel  necessary  for  vitality,  261. 

Functions,  gradation  of,  11. 

animal,  81. 

chemical,  38. 

mechanical,  30. 

natural,  81. 

sensorial,  13.  { 

vital,  81. 

Furcular  bone,  1005. 
Gagliardi,  143. 
Galen,  722,  1136. 
Gall,  584,  725. 
Gallendobff,  368. 
Ganglia,  581,  590,  726,  747. 
Ganglia,  lymphatic,  543. 
Gas,  346,  374. 
Gasteropoda,  1083- 
Gastric  juice,  39,  323,  340. 
Gelatin,  279. 

Gelatinous  secretions,  516. 
Gemmules,  784,  1113,  1117. 
Generation,  50,  780. 
Geology,  71. 
Georget,  868  (note). 
Germ,  786. 
Gestation,  50. 
Gibson,  547. 
Gills,  1045,  1060- 
GirafFe,  993. 
Gizzard,  1009. 
Glands,  43,  494,  845. 

,  lymphatic,  543,  552. 

Gland ulae  ceruminosse,  653. 

Hardsri,  929. 

Meibomii,  653. 

Glandular  system,  496. 
Glans,  800, 
Glisson,  93,  203. 
Globules  of  milk,  520. 

of  blood,  392. 

Globular  tissue,  115. 

Globuline,  397. 

Glottis.  760. 

Glue,  279. 

Gluten,  314,  391. 

Gmelin,  348,  370,  372  (note),  380, 

Good,  436. 

Gordon,  179,  386. 

Graafian  vesicle,  797,  820,  829. 

Gradation  of  functions,  11. 

of  po Vipers,  98. 

Granular  tissue,  115. 
Greeks,  1126. 
Gregory.  558  (note). 
Growth,  46,  262,  570. 
Grtjithuisen,  432  (note). 


510 


INDEX. 


Gubernaculum,  849. 

GUENEAU     DE     MoNTBEILLARD,    154 

(note). 
Gums,  6U8. 
GuRLT,  183  (note). 
GuYOT,  615. 
Gymnotus,  1070. 

Hair,  184. 

Hales,  452. 

Halitus,  135,  384. 

Hall,  741,  747. 

Haller,   112,  436    (note),  1157, 

passim. 
Hamberger,  436. 
Hamster,  960. 
Hand,  256,  260,  899. 
Hare,  961. 
Harlan,  450  (note"). 
Hartley,  692. 
Hartsoeker,  810. 
Harvey,  442,  820,  1149. 
Hatchett,  289. 
Havers,  canals  of,  140. 
Hays,  657  (note). 
Hearing,  18,  623,  636,  927. 
Heart,  41,  409,  459,  744,  841,  920. 
Heat,  animal,  489. 

sense  of,  595. 

Helix  of  ear,  627. 
Hematine,  397. 
Hematosine,  397. 
Henry,  290. 
Herissant,  141. 
Herophilus,  720,  1134. 
Hewson,  387,  393. 
Hidrophorous  ducts,  555  (note). 
Hippocrates,  691,  1128. 
History  of  Physiology,  1121. 
Hock  bone,  982. 
HooKE,  198. 

HODGKIN,  116,  200. 

Hoffmann,  101,  1156. 

Hog,  974. 

Holothuria,  1110. 

Home,  371,  639,  668. 

Honey-comb  stomach,  939. 

Horns,  993. 

Horse,  978. 

Houston,  809. 

HowsHip,  140. 

Human  peculiarities,  891. 

Hunger,  321,  596. 

Hunter,  Wm.  113,  118,  169,  181. 

Hunter,  John,  1158,  et  passim. 

Hybernation,  47. 

Hydrogen,  271. 

Hygrometric  property,  129. 

Hymen,  818. 


Ideas,  703. 
Ileum,  40. 

Illusions,  visual,  681. 
Images  in  the  eye,  659. 
Imbibition,  1097. 
Impressions,. 94,  578. 
Incident  nerves,  741. 
Incubation,  1019. 
Incus,  631. 
Induction,  78. 
Infundibulum,  633. 
Infusoria,  1120. 
et     Ink  of  Sepia,  1082. 
Insanity,  701. 
Insalivation,  331. 
Insects,  1097. 
Insectivora,  939,  940. 
Inspiration,  471,  472. 
Instinct,  732. 
Instinctive  motions,  733. 
Integument,  176,  930. 
Intention  in  organization,  9. 
Intercostal  muscles,  473. 
intermaxillary  bone,  915. 
Interspinal  bones,  1048. 
Interstitial  absorption,  .551. 
Intervertebral  ligament,  238. 

substance,  154. 

Intestines,  40,  370. 
Intestines  large,  373. 
Involuntary  motions,  736. 

muscles,  579. 

Iris,  646,  663,  669. 
Iron  in  the  blood,  398. 
Irritability,  93. 

of  heart,  456. 

Irritation,  94,  578. 
Isthmus  Vicussenii,  412. 
Itching,  597. 

Jacobson's  gland,  931. 
Jejunum,  40. 
Jelly,  280. 
Joints,  168,  244. 

Kangaroo,  954. 
Kater,  396. 
Kay,  488  (note), 
Keill,  436. 
Kidney,  .556,  847,  926. 
Kiernan,  524. 

Labyrinth  of  the  ear,  632. 
Lacerti,  194. 
Lacrymal  duct,  618. 

gland  and  sac,  654. 

I  Lactation,  50,  836. 
Lacteals,  40,  538. 
Lacteal  absorption,  376. 


IXDEX. 


511 


Lactic  acid,  520. 
Laws  of  nature,  89. 
Lacunee,  506,  800. 
Lamina  cribrosa,  651. 

spiralis,  633. 

Lancisi,  392. 

Larva,  1100. 

Larynx,  764. 

Lassaigne,  372. 

Lavoisier,  555. 

Laws  of  vitality,  86,  103. 

Lecanu,  397,  407. 

Lee,  Robert,  825. 

Leewenhoek,   182,    183,  195,  392, 

428,  824, 1153. 
Lemur  tardigradus,  936. 
Lens,  648. 

Lepelletier,  511  (note). 
Leuret,  372. 
Levirostres,  1022. 
Ligaments,  30,  84,  155. 

alar,  170. 

articular,  245. 

capsular,  172. 

crucial,  172. 

fascicular,  172. 

lateral,  172. 

round,  849. 

vocal,  762. 

Ligatures  on  vessels,  443. 

Light,  655. 

Limbs  in  general,  241,  843. 

Lingual  bone,  1018. 

Lining,  ^58  (note). 

LiNN^Tjs,  62,  562. 

Lion,  948. 

Lips,  607. 

Liquid  of  surfaces,  135. 

Liquor  aranii,  844. 

Liquor  Morgagni,  648. 

Lister,  116,  200. 

Liver,  40,  522,  524,  560. 

Lizard,  1032. 

Lochia,  835. 

Locomotion,  28. 

Loculi,  505. 

Lobster,  1095. 

Lower  extremities,  246. 

Lungs,  49,  408,  554,  846,  1013. 

LUZURIAGA,  387. 

Lymph,  546. 
Lymph  globules,  400. 
Lymphatics,  539,  547. 
Lymphatic  absorption,  45. 
Lymphatic  glands,  495,  542,  552. 
Lymphatic  hearts,  1043. 

Macaibe,  362  (note). 


Macavoy,  Miss,  678. 

Macleay,  70. 

Magendie,  84  (note),  319,  320  (note), 
374,  387  (note),  511  (note),  549, 
669  (note),  720,  722,  755. 

Magnetism,  animal,  755. 

Malay  race,  876. 

Male  system,  805. 

Malleus,  631. 

Malpighi,  141,  178,  179,  392,  428, 
502,  584,  1153. 

Mammalia,  891,  910. 

Mammaj,  793,  826. 

Manati,  1001. 

Mandril,  935. 

Manganese  in  the  blood,  407. 

Mantle  of  moUusca,  1077. 

Manyplies  stomach,  988. 

Marcet,  359,  362  (note),  405. 

Mariotte,  674. 

Marmot,  960. 

Marrow,  125,  145. 

Marsupial ia,  952, 

Marsupium,  1015. 

Mascagni,  113,  165,  543. 

Mastication,  39,  327. 

Mastoid  cells,  630. 

Materialism,  576,  705. 

Mascagni,  378  (note). 

Mayo,  87,  615,  638,  711,  737,  755. 

Meatus  auditorius,  628. 

Mechanical  functions,  30,  36. 

Mechanism  of  respiration,  470. 

Meckel,  116,  -378  (note). 

Meconium,  851. 

Medicine,  58. 

Medulla  oblongata,  582,  730. 

Medullary  substance,  14. 

Medusa,  1116. 

Melancholic  temperament,  864. 

Membrana  granulosa,  790. 

nictitans,  930. 

papillaris,  841. 

tympani,  629. 

vascularis  Halleri,  106.5. 

vitelli,  1019. 

Membrane,  33,  127. 

Menghini,  398. 

Menstruation,  819. 

Merry-thought,  1005. 

Mesenteric  glands,  543. 

Mesmerism,  755. 

Metaphysics,  4. 

Microscopical  observation,  116,449. 

Miescher,  142  (note). 

Mitchell,  J.  K.,  450  (note). 

Milk,  318,  520,  828. 

Milk  teeth,  855. 


512 


INDEX. 


Mind  distinct  from  matter,  576,  577, 

705. 
MojoN,  378  (note). 
Mole,  939. 
Mollusca,  68,  1074. 
Mongolian  race,  873. 
Monotremata,  965. 
Monro,  143,  242,  394,  585,  588. 
MORGAGNI,  611,  648. 
Motion,  voluntary,  23. 
Motor  nerves,  719. 
Movements,  animal,  27. 
Mucous  follicles,  611. 

layer,  837. 

membranes,  185,  493. 

secretions,  187,  51. 

Mucus,  302. 

MiiLLER,  340  (note),  436,454  (note), 

487  (note),  509,  563,  569,  801. 
Multivalves,  1085. 
Mundinus,  1140. 
MuRATORi,  366  (note). 
Mas  typhi  us,  959. 
Muscles,  26. 
Muscular  action,  201,  202. 

power,  26,  93,  219. 

structure,  193. 

sense,  602. 

Muscularity  of  arteries,  462. 
Musical  note,  757.      • 
MuYS,  196. 
Myopia,  675. 


Nails,  184. 

Natural  methods  of  classification,  64. 

Natural  Philosophy,  1,  2. 

Natural  history,  72. 

Nausea,  621. 

Needham,  826. 

Negro  race,  874. 

Neighing,  984. 

Nerves,  14,  581,  586. 

motor,  25. 

sensiferous,  25. 

influence  on  digestion,  352. 

influence  on  temperature,  490. 

influence  on  secretion,  535. 

Nervous  substance,  14. 
Nervous  system,  14,  578,  581, 1062, 
1091. 

,  types  of,  68. 

Nervous  temperament,  867. 

Neurilema,  587. 

Neurolhelic  apparatus,  178  (note). 

Newport,  1099. 

Nictitating  membrane,  929. 

Nitrogen,  270. 


Nitrogen,  absorption  of,  483. 
Nutrition,  37,  38,  46,  562. 
Nutritious  principle,  317. 
Nutritive  matter  required,  261. 
Nymphee,  818,  1100. 

Obliquity  of  muscular  fibres,  217. 

Occipital  angle,  909. 

Ocular  spectra,  684,  685. 

CEsophagus,  715,  1061 . 

Oil,  319. 

Oily  matter  in  blood,  407. 

Oleaginous  secretions,  518. 

Omphalo-mesenteric  vessels,  841. 

Operculum,  1083. 

Ophidia,  1035. 

Opossum,  953. 

Optical  laws,  655. 

Orang  Utan,  905,  932,  933. 

Orbicular  bone,  631. 

Orbiculus  ciliaris,  647. 

Organic  aflinities,  86,  92,  103,  536. 

molecules,  826. 

phenomena,  6. 

Organization,  110. 
Ornithorhyncus,  966. 
Orthoptera,  1101. 
Os  quadratum,  1008. 
Os  tincse,  817. 
Osseous  fabric,  35,  137. 
Ossicula  auditus,  631. 
Ossification,  565. 
Osmazome.  407,  526. 
Ostrich,  1021. 
Ovary,  797. 
Ovisac,  801,  802,  803. 
Ovists,  823,  825. 
Ovulum  et  ovum,  800. 
Ox,  995. 
Oxygen  in  respiration,  481. 

Pachydermata,  968. 
Package  of  organs,  173. 
Palate,  609. 
Paley,  75. 
Palpebrae,  653. 
Pain,  598. 
Pancreas,  40. 
Pancreas  Asellii,  922. 
Pancreatic  secretion,  40,  365. 
Panizza,  615  (note). 
Panniculus  carnosus,  930. 
Papillae,  cutaneous,  178. 

of  tongue,  610. 

Pappenheim,  352  (note). 
Parallactic  aberration. 
Parenchyma,  animal,  667. 
Parmentier,  385,  428. 


INDEX. 


513 


Parturition,  50,  735. 

Pastern  bone,  979. 

Pathology,  55. 

Paunch,  988. 

Peccari,  975. 

Pecora,  64. 

Pecquet,  377,  1151. 

Pelvis,  240. 

Pencillated  structure,  532. 

Penis,  808. 

Penniform  muscle,  315. 

Pepsine,  340  (note). 

Perception,  13. 

Pericardium,  133,  409. 

Perichondrium,  147. 

Perilymph,  632. 

Periosteum,  144,  146. 

Peristaltic  action,  338. 

Peritoneum,  133. 

Perspiration,  515,  555. 

Petasiolus  granulosus,  803,  830. 

Petit,  circle  of,  650. 

Phantascope,  681. 

Phascolame,  955. 

Phenikisticope,  681. 

Philip,  96,  352,  464,  741,  742,  744. 

Philosophy  of  mind  and  matter,  21. 

Phlegmatic  temperament,  866. 

Phosphorus,  268. 

Phrenology,  814  (Appendix). 

Physical  and  vital  laws,  89. 

Physical  sciences,  1,  2,  21. 

Physiology,  general  views,  1. 

object  of,  10. 

applications  of,  57. 

to  medicine,  58. 

to  zoology,  60. 

to  geology,  71. 

to  natural  theology,  74. 

Phy  tology,  4. 
Pia  mater,  133. 
Picromel,  .367. 
Pineal  gland,  495,  698. 
Pigmentum  nigrum,  671. 
Pituitary  membrane,  618. 
Placenta,  833. 
Plan  of  animal  creation,  73. 
Planch,  436. 
Plantigrada.  941. 
Plato,  1130. 
Pleurae,  133. 
Plexus,  586. 
Poison-teeth,  1038. 

POISEUILLE,  460. 

Polygastrica,  1120. 
Polypi,  1118. 
Pomum  Adami,  759. 
Pores  in  cuticle,  183. 


Portal  system,  427, 523,  524. 

PORTKRFIELD,  242. 

Porus  opticus,  651. 

Powers,  vital,  98. 

Prehension,  29. 

Presbyopia,  675. 

Pressure,  593. 

Prevost,  199,  222. 

Prichard,  887. 

Priestley,  692,  note. 

Primitive  trace,  831,  1020. 

Proboscis  of  elephant,  968. 

Processus  mam_millares,  925. 

Prochaska,  197,  585. 

Promontory  of  ear,  630. 

Proteus  anguinus,  1044. 

Proust,  557. 

Prout,  318,  352  (note),  362,  485, 

558  (note). 
Proximate    animal  principles,    272, 

277. 
Prussic  acid,  270. 
Psychology,  21. 
Psychological  relations  of  sensorium? 

748. 
Ptolemies,  1132. 
Puberty  in  the  male,  812. 

female,  812,  819. 

Pulmonary  circulation,  439,  466. 

exhalation,  484. 

Pulse,  461. 

Puncta  lachrymalia,  654. 
Punctum  saliens,  1020. 
PuRKiNJE,  352  (note). 
Pylorus,  353. 
Pythagoras,  1127. 

Quadrumana,  932. 

Racoon,  943. 

Racornissement,  226. 

Radiata,  68. 

Raspail,  368,  386  (note). 

Rat,  958. 

Reason,  732. 

Reaumur,  343. 

Receptaculum  chyli,  377. 

Recipient  organs,  131. 

Recurrence  of  impressions,  702. 

Red  globules,  392. 

Reed  of  ruminants,  988. 

Rees,  142. 

Reflex  function,  741. 

Reflexion  of  light,  657. 

Refraction  of  light,  656. 

Reil,  584,  588. 

Rein-deer,  994. 

Relaxation,  muscular,  207. 


514 


INDEX. 


Remak,  588  (note). 
Renal  capsules,  495. 
Renewal  of  materials,  44,  570. 
Reparation,  46,  262. 
Reparatory  functions,  307.  • 
Reproduction,  50,  783. 
Reptiles,  1024. 
Resinous  secretions,  521. 
Respiration,  38,  49,  468,  1060, 
Respiratory  muscles,  728. 

nerves,  723. 

Rete  Malpighianum,  179. 

mirabile,  991. 

mirabile  Malpighii,  466. 

mucosum,  179. 

testis,  806. 

Retina,  645. 
Rhinoceros,  973. 
Rhizostoma,  1117. 

RiCHERAND,  82. 

Rodentia,  956. 

RoGET,  88,  222,  349,  668,  681. 

Roosting,  1008. 

ROUELLE,  407. 

RoussEL  DE  Vauzeme,  183  (note), 
555  (note). 

RUDBECK,  1151. 

RuDOLPHi,  135  (note),  378  (note), 

888. 
Rugse  palati,  609. 
Ruminants,  986,  1101. 
Rumination,  989. 

RuYscH,  113,  178,  503,  584, 1154. 
Ruyschian  tunic,  645,  928. 

Sabatier,  511  (note). 

Saccharine  principle,  316. 

Saccho] actio  acid,  519. 

Sacculus,  634. 

St.  Hilaire,  Geoffroy,  73, 1050. 

Salamander,  1043. 

Saline  secretions,  527. 

Saliva,  39,  332. 

Salivary  glands,  612. 

Sanguification,  41,  382. 

Sanguiferous  system,  413. 

Sanguine  temperament,  863. 

Sanson,  657  (note). 

Sauria,  1031. 

Savigny,  72. 

Scalag  cochlear,  633. 

Scaphus,  627. 

SCHEELE,  556. 

Schneiderian  membrane,  618. 

Schwann,  340  (note). 

Schroder  van  der  Eole,  386  (note). 

Sclerotica,  644. 

Scrotum,  805. 


Scudamore,  386. 

Seal,  949. 

Seat  of  the  soul,  698. 

Sebaceous  glands  and  follicles,  189, 

931. 
Secretion,  38,  43,  491. 
Secretion,  theory  of,  529. 
Secretions,  513. 

albuminous,  514. 

aqueous,  512. 

gelatinous,  516. 

fibrinous,  517. 

oleaginous,  518. 

resinous,  521. 

saline,  -527. 

Seguin,  555. 

Semen,  810. 

Semicircular  canals,  632. 

Senac,  390. 

Sensation,  13,  21,  95,  578. 

laws  of,  677. 

theories  of,  691. 

Sefises,  external,  16,  592. 
Sensibility,  organic,  740. 
Sensiferous  nerves,  25,  719. 
Sensorial  functions,  13,  574,  923. 
Sensorial  power,  96. 
Sensorium,  578,  695,  697,  699. 
Sepia,  1079. 
Septum  narium,  617. 

vetriculorum,  407. 

Serosity,  403. 

cellular,  120. 

of  the  blood,  390. 

Serous  capillaries,  433. 

layer,  829. 

membranes,  133,  493. 

Serpents,  1035. 
Sleep,  995. 
Shoulder-joint,  255. 
Sight,  17. 

Silurus  electricus,  1070. 
Simple  bodies,  275. 
Sinus  medianus,  1067. 

terminalis,  842. 

valsalvae,  410. 

venosus,  410. 

Sinuses,  425. 

nasal,  616. 

Siren,  1044. 
Skeleton,  30, 137,227. 
Skey,  200. 
Skin,  176,  843. 

excretion  by,  555. 

Skull,  229. 
Sleep,  752. 
Sloth,  964, 
Smell,  19,  616,  619,  926. 


INDEX. 


515 


Socrates,  1130. 

SoMMERING,  651. 

foramen  of,  651. 

Solids  and  fluids,  111. 

Solipeda,  976. 

Solvent  power  of  gastric  juice,  343. 

Somatology,  21. 

Somnambulism,  754. 

Sound,  623. 

Sound  of  fishes,  1061. 

Spallanzani,  343,  454,  819. 

Specific  gravity  of  muscles,  208. 

Spectra,  ocular,  684. 

Speech,  24. 

Spermatic  animalcules,  810. 

cord,  797. 

Spermatists,  theory  of,  82. 

Spermatozoa,  810. 

Spherical  aberration,  664,  666. 

Sphincters,  212. 

Spinal  cord,  581,'  842. 

Spine,  236,  911. 

Spiracles,  1097. 

Spirit  of  animation,  7. 

Spirits,  animal,  691. 

Spleen,  371,  495. 

Splint  bone,  979. 

Sporules,  785. 

Spurzheim,  584,  725. 

Stahl,  1156. 

Standing,  247. 

Stapes,  631. 

Stark,  319. 

Stellated  structure,  533. 

Steno's  duct,  612. 

Stevens,  343. 

Stigmata,  1097. 

Stimuli,  93,  203. 

Stomach,  39,  338. 

Straight  muscles  of  the  eye,  668. 

Stuart,  198. 

Sublingual  gland,  612. 

Submaxillary  gland,  612. 

Sudoriferous  ducts,  555  (note). 

Sugar,  316. 

Sugar  of  milk,  520. 

Sulphur,  270. 

Surfaces,  liquid  of,  -515. 

Sutures,  233. 

Swammerdam,  198,  1154. 

Swimming  bladder,  1061. 

Symmetrical  system  of  nerves,  722. 

Sympathetic  nerves,  747. 

Sympathy,  735. 

Syngenesis,  823,  826. 

Synovia,  170. 

Systemic  circulation,  439, 

Systole  of  the  heart,  441. 


Tabula  vitrea,  231. 
Tannin,  test  of  gelatin,  282. 
Tapetum,  928. 
Tapir,  972. 
Tardigrada,  963. 
Tarsus,  653. 
Taste,  20,  604,  613. 
Teeth,  328,  568,  902,  916. 
Temperaments,  .52,  859. 
Temperature,  animal,  489. 

sensation  of,  .595. 

influence  on  digestion,  348,  386. 

requisite  for  sensation,  688. 

Tendons,  34,  35,  156,  163,  213. 

Tendinous  sheaths,  160. 

Testes,  80.5,  849. 

Thackrah.  386  (note),  402  (note). 

Thaumatrope,  681. 

Thenard,  367,  407. 

Theology,  natural,  74. 

Thilenius,  142  (note). 

Thirst,  325,  596. 

Thomson,  A.  794. 

Thomson,  287,  .558  (note). 

Thoracic  duct,  545. 

Thorax,  bones  of,  23-5. 

Thumb,  258. 

Thymus,  495,  851. 

Thyroid  gland,  495,  761. 

Tiedemann,  347, 368,  372  (note),  378, 

Tingling,  597. 

Todd,  340  (note). 

Touch,  16,  .593. 

Tone,  175. 

Tongue,  329,  606,  610,  1018. 

Tonicity,  175,  224. 

Torpedo,  1070. 

Tortoise,  1027. 

Tracheae,  766,  1097, 

Tragus,  626. 

Transfusion  of  blood,  447. 

Travers,  669. 

Tremulous  action  of  muscles,  22.5. 

Treviranus,  1. 

Tuberculum  Loweri,  412. 

Tunica  albuginea,  652,  797. 

conjunctiva,  653. 

granulosa,  804. 

' Ruyschiana,  928. 

vaginalis,  797. 

Turbinated  bones,  617. 
Turner,  387. 
Turtle,  1027. 
Tympanic  bone,  924. 
Tympanum,  629,  630. 

Umbilical  cord,  851. 
Upper  extremities,  254. 


516 


INDEX. 


Urachus,  848. 
Urea,  407,  525,  559. 
Urethra,  808. 
Urine,  556,  557. 
Uroline,  407. 
Uterus,  816,  817. 
Utero-gestation,  785,  829. 
Utricle,  634,  1067. 
Utricali,  505. 
Uvea,  646. 
Uvula,  609. 

Vagina,  817. 

Valentin,  588  (note),  809  (note). 

Vallisneri,  817. 

Valves,  438,  444. 

ofheart,  410,  411. 

of  lacteals,  378. 

Valvulas  mitrales,  410. 

Valvulss  semilunares,  411. 

Vampire  bat,  938. 

Van  Helmont,  101. 

Vanhorne,  1154. 

Varieties  in  human  race,  53,  869. 

Vas  deferens,  797. 

Vasa  inferentia,  543. 

Vascular  area,  841,  850. 

Vascular  layer,  837. 

Vascularity,  113,  435. 

Vauquelin,  399,  520. 

Vegetable  food,  314. 

Velpeau,  833  (note). 

Velum  pendulum  palati,  609. 

Veins,  42,  425. 

Velocity  of  sound,  624. 

Vena  portae,  427. 

Vena  terminalis,  1020. 

Venous  absorption,  45  (note),  549. 

Venous  system,  425. 

Ventricles,  409. 

of  the  br-ain,  583. 

of  the  heart,  455. 

Ventriculus  succenturiatus,  1009. 
Vernix  caseosa,  843. 
Vertebra,  236. 
Vertebrata,  68. 
Verumontanum,  807. 
VeS  ALIUS,  1143. 
Vesicula  alba,  844. 

intestinalis,  847. 

seminalis,  811. 

Vessels,  131. 
Vestibule,  632. 


Vibrations,  692. 
VicQ  D'AzYR,  82. 
Villi,  187,  532. 
Vis  a  tergo,  465. 
Vis  insita  of  Haller,  93. 
Vis  medicatrix,  101. 
Vision,  17,  640,  660. 
Vital  powers,  89,  92,  103. 
Vital  principle,  86,  100,  106. 
Vitality  of  the  blood,  389. 
Vitelline  sac,  844. 
Vitreous  humor,  648. 
Vitrine  auditive,  632. 
Vocal  ligaments,  762. 
organs,  900. 

VOGEL,  386. 

VoisiN,  364  (note). 

Voice,  24,  756. 

Volition,  577,  709. ' 

Voluntary  motion,  13, 23, 25, 378,  709. 

Vomer,  617. 

Vowel  sounds,  770. 

Walking,  251. 
Walrus,  951. 
Weasel,  945. 
Wedembyer,  432  (note). 
Weber,  594. 
Weinholt,  407. 
Wells,  399. 
Wendt,  183  (note). 
Wenzell,  585. 
Whale,  1002. 
Wharton's  duct,  612. 
Wheatstone,  615,  757. 
Whytt,  1158. 
Williams,  488  (note). 
Willis,  764. 
Withers,  976. 
Wolff,  847. 
Wolffian  bodies,  847. 

WOLLASTON,  225. 

Woodpecker,  1023. 
Worms,  1092,  1112. 
Wounds  of  arteries,  447. 
Wrist,  256. 

WURZER,  407. 

Young,  395,  396,  397,  436,  511,  639, 
668,  755. 

Zoology,  3,  5,  60. 
Zoophytes,  1105. 


THE  END. 


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